Science of weight loss

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Physics

In everyday life, energy is neither created nor destroyed. It just moves about, or changes form. The way physicists phrase it is, if you isolate a system so no energy leave it, or enters it from outside, then the amount of energy in the system is conserved - it stays the same, the total quantity doesn't change over time.

Physicists tend to measure energy in units called "Joules". A small apple masses about 100 grams. If you put it on a set of scales, it exerts a force of 1 Newton upon the scales, due to its weight in the Earth's gravitational field. If you raise that apple directly upwards by 1 meter (that's just over a yard), then the muscles in your arm have done 1 Joule of work.

If you weigh 50 kg (just under 8 stone) and you walk up a couple of flights of stairs (say 8 meters, which is about 26 feet), then you've done 50 x 8 = 400 Joules

Biologists use a unit call the "Calorie" (symbol: cal). To convert from Joules to Calories, divide by 4. So 400 Joules is about 100 Calories. That's actually a pretty small amount of energy, so when they label food, they generally use Kilocalories (symbol: kcal, or Cal) though, confusingly, people are sometimes lazy and just abbreviate that to "Calorie".

Suppose you have a 1 kilogram bottle of water. (That's about half the size of a 2 litre bottle of coke.) 1 kilocalorie is the energy required in order to raise its temperature 1 °C, to lift it vertically by 400 meters, or to accelerate it horizontally from rest to a speed of 90 meters per second.

The human body stores energy as chemical potential energy. We'll go into how it does that in a moment, but the important thing to take away from the physics section is that this isn't a mysterious process. It is very well defined.

CHANGE IN ENERGY STORED = ENERGY IN - ENERGY OUT

The energy we store in our body increases when we take in food, and decreases when the muscles and organs in our body expend energy by moving about or just ticking over, keeping the body warm and active.

If, during a day, you take in 1000 kilocalories of energy, but you expend 1500 kilocalories of energy, by the end of the day your body will be storing precisely 500 less kilocalories of energy than it was at the start of the day. There is no uncertainty in this. No willpower or hormones involved. It is as much a law of phyiscs as the amount of electricity needed to boil a kettle.



Chemistry

Atoms are joined together into molecules by chemical bonds. You can think of them as elastic bands. The tighter the bond, the more energy is required to break it. By moving the atoms into a configuration where the bonds are tighter, energy is released. This is how chemical potential energy is stored. The process of changing which atoms are connected to which is known as a chemical reaction. Some chemical reaction use up energy. Others release energy.

The cells in human bodies are powered by a chemical reaction in which Adenosine Triphosphate (known as ATP, or by its formula: C10H16N5O13P3) is converted into Adenosine Diphosphate (known a ADP, or by its formula: C10H15N5O10P2). We can make ATP from a number of sources: Glucose (C6H12O6), Ketones (such as Acetone: C3H6O) or Fatty Acids (such as Acetic Acid: C2H4O2). Glucose circulates in the blood stream when needed, and a certain amount is stored in cells as Glycogen. For longer term storage the remainder of the energy is stored as fatty acids, mostly in fat cells of the brown and white adipose tissue. Ketones are generally only produced during prolonged fasts once the body runs out of stored glycogen.

The human body is pretty efficient at transforming from one chemical form to another so, as long as the digestive process is working correctly, we can approximate the energy that the human body will take in from eating a piece of food by the total energy produced if that piece of food is completely incinerated. The device used to measure this is called a Calorimeter. A more precise estimate can be worked out by calculating the percentage of the food made up from Carbohydrates, Fats and Proteins because we know, from practical experimentation, how many Kilocalories an average working human body takes in from digesting 1 gram of each:
. Protein: 1 gram = 4 Kilocalories
Carbohydrates: 1 gram = 4 Kilocalories
. Alcohol: 1 gram = 7 Kilocalories
. Fat: 1 gram = 9 Kilocalories

We'll look later at how the precise mix affects hunger and insulin production, and of course it is important for your health's sake to have a balanced diet that contains all the vitamins and nutrients your body needs, but as far as the chemistry of energy storage goes, it doesn't matter whether you are eating spinach or chocolate ice cream. A calorie is a calorie. The only way to reduce the "ENERGY IN" part of the equation is to reduce the number of calories you put in your mouth.



Biology

So how much 'should' you weigh?

In the 19th century, Adolphe Quetelet came up with Body Mass Index (BMI) which was Height (in meters) divided by ( Weight (in kilograms) squared ). A German later came up with a the Ponderal Index (Height divided by Weight cubed) which scaled a bit better. In fact the exponent should probably be about 2.6 (source), but people have stuck with the BMI, since the whole thing is only an approximate guide to fitness because it ignores the difference between muscle and fat.

A better guide is the Body Fat Percentage (BFP) which is the percentage of a person's total weight that is due to fat, but it is harder to calculate. The most accurate method is to use a bath to calculate your volume, then take advantage of the fact that fat has a lower density than bones, muscles and organs, to work backwards using one of two formulae, depending on how muscular you are:

MUSCULAR (Siri) BFP = [(4.950 / Body Density) - 4.500] * 100
NOT MUSCULAR (Brozek) BFP = [(4.570 / Body Density) - 4.142] * 100

(source: link and link)

However you can get a pretty good estimation of your BFP by starting with your BMI, then taking your age, gender into account:

Child BFP = (1.51 x BMI) - (0.70 x Age) - (3.6 x gender) + 1.4
Adult BFP = (1.20 x BMI) + (0.23 x Age) - (10.8 x gender) - 5.4
( where male gender= 1, female=0 ).

One needs a certain minimum amount of fats in the body for it to function at all (it does things like protect vital organs and store certain vitamins). The numbers pan out at:

Description Women Men
Essential fat 10-13% 2-5%
Athletes
14–20% 6-13%
Fitness 21–24% 14–17%
Average 25–31% 18–24%
Obese
32%+ 25%+


Ok, so how about the other part of the equation (ENERGY OUT) ?

There are three components:

Energy used by your body while at rest - Basal Metabolic Rate (BMR)
Energy used by your digestive system
Energy used by being active - Active Metabolic Rate (AMR)


Even when you're asleep and not digesting you're still using energy. Of the base energy you use, approximately 10% powers the heart, 20% powers the brain, 40% powers the liver and kidneys and 30% powers miscellaneous other stuff (mainly muscles).

Thermostasis (keeping the body at a constant temperature) and digestion can increase this base level by, on average, a further 10%. We generate heat using the brown adipose tissue and, when that's not enough, in the muscles by shivvering. How long the digestive system burns for, and how hotly, depends on what you've eaten:

Image

This is why skipping breakfast can be counter-productive. You're better off (from a weight loss point of view) with spreading your calories between several meals to keep the digestive system working most of the day.

Anerobic fitness does not, alas, increase your BMR. But muscle mass does. The more muscle you have, the more energy your body burns, even when at rest. You can make a rough prediction of your BMR just from your height, weight, age and gender:

Image

P = \left ( \frac {10.0 m} {1 ~ \mbox {kg}} +
\frac {6.25 h} {1 ~ \mbox {cm}} - \frac {5.0 a} {1 ~ \mbox {year}} + s
\right ) \frac {\mbox {kcal}} {\mbox {day}},

( where s = +5 for males and −161 for females )

however if you know your BFP you can use that to calculate your Lean Body Mass (LBM)

LBM = Weight x (100 - BFP) / 100

and from that you can get a better estimate:

P = 370 + ( LBM x 21.6 )

(If you don't like formulae, there's a handy web page that does all the calculations for you.)



Your Active Metabolic Rate can add onto your Basal Metabolic Rate an amount that is equivalent to multiplying the BMR by between 1.2 and 1.9, depending on your activity level:

Sedentary = BMR X 1.2 (little or no exercise, desk job)
Lightly active = BMR X 1.375 (light exercise/sports 1-3 days/wk)
Mod. active = BMR X 1.55 (moderate exercise/sports 3-5 days/wk)
Very active = BMR X 1.725 (hard exercise/sports 6-7 days/wk)
Extr. Active = BMR X 1.9 (hard daily exercise/sports & physical job or 2X day training, i.e marathon, contest etc.)

So, for instance, if your BMR is 1000 Kilocalories per day, and you have a sedentary lifestyle, your AMR will add 200 Kilocalories to how much you burn each day, for a total of 1200 Kilocalories per day.

Summary so far

Step 1 - Weigh yourself

Step 2 - Calculate what weight you want to achieve

Step 3 - Decide how quickly you want to achieve it
(Note: trying to lose weight too fast is counter productive, because it burns up muscle as well as fat. They recommend not eating less than 80% of your BMR. Eating 500 fewer calories than you expend per day translates to a weight loss of about 1 pound per week, which is fine. You don't want to lose more than 2 pounds per week, if it is going to be sustainable.)

Step 4 - Calculate how many calories you burn each day (BMR + AMR)

Step 5 - Calculate how many calories you need to eat each day in order to achieve your target

Step 6 - Eat only that many calories



Step 6, for most people, is the hardest part, and it leads us onto the next section: Psychology

But first, some useful webpages to do with the first 5 steps:

* Calculators from Forever Living
* BMR from Shape Fit
* Daily Calorie Needs from Health Recipes
* AMR from Prevent Disease
* Advice from Get Physically Fit

(Note: there while most of these figures are accurate there are genetic and medical factors that can vary things enormously. Specifically some people just naturally have high BMRs, while others have to struggle with enormous will power just to maintain a constant weight because their BMR is very low for their activity level. There is some evidence that this is affected by the diet your parents ate before conception and during pregnancy.)
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Environment

In order to truly understand the psychology of eating, it is necessary first to consider the environment in which we evolved and the problems to which our current biological mechanisms regulating hunger are solutions.

In most parts of America and Europe, food is plentiful. We can predict that, if we nip down to the supermarket, there will be shelves filled with a wide range of fruit, meat, vegetables, grains and dairy products, even in the middle of winter. And they generally have convenient labels on them, listing not only their Kilocalories, but also what percentage of the recommended daily amount of iron, fat soluble vitamins, etc they contain per portion.

But evolution takes many many generations to make appreciable changes, and that's not the environment a majority of our ancestors lived in. 20,000 years ago we lived in tribes or extended families, eking out an existence by hunting and gathering. The food supply was rarely plentiful, and those periods of plenty were only partially predictable. Gathering plants, nuts and crawling insects is time consuming, and may be very low on certain nutrients the body needs. So when the body bit into something that had a lot of something it was low on, it developed a mechanism for motivating the person, saying "Like! I need this! Eat as much as you can of this, even to the point of the stomach getting dangerously full."

And it is not a case of just looking at current deficits. The body developed ways of looking ahead. It could 'think' "I may not need these calories to function in the next 24 hours, but winter is coming on, and food has been very unpredictable, so I better stock up in advance.". The same happens on shorter time scales. It can learn "Someone has killed a deer, and the tribe is gathering for a meal. I may be ok on blood sugar now, but if I don't eat now it will be all finished in an hour's time."

The body also has to take into account that seeking out food wasn't a matter of going downstairs in the middle of the night to raid the fridge. If it was dark, or the body was injured, or there was danger outside, the body was better off postponing the search for food until some was actually likely to be found at a lower cost in energy than the hunt would return.



Types of Hunger

So how has the human body adapted to these various pressures and considerations?

The answer is that our decision to seek out food and eat (or not), and what, it is affected by several different types of motivation, including more than one which we label "hunger". The strength of these motivations are regulated by a very complex web of chemicals circulating in the bloodstream; some of which are caused by various organs (such as the stomach being physically full, or the liver sensing low glucose levels); some of which come via the brain (the sound of bacon sizzling, a scent, a memory of a scent, cramping from an empty stomach) ; some of which trigger or suppress others.

And some motivations to do with eating have nothing to do with hunger. People often eat from habit, or to seem social, even when they have no physical need for the kilocalories or nutrition in the food. Others avoid eating, not because they are sated, but because of cultural ideas about 'ideal' body size and shape, or because their body has 'learned' an aversion to specific foods and associates them with a previous food-poisoning incident.

However for the next few sections I'm going to focus on four things:

Emptiness-type hunger - You feel low on energy, your stomach feels hollow, it's chow time! Get something to eat, it doesn't matter what, but eat it now, the first thing to hand.

Craving-type hunger - You've had something to eat but you're just not satisfied, there's a particular food or type of food you're dreaming of, salivating at the thought of, that you just can't get enough of

Not-meal-time satiety - The meal is over, or there is no food available, so no profit in having a hunger to force you to spend time looking for more food that isn't there right now, go do something else or go back to sleep

Food-not-attractive satiety - It is Christmas day and you're stuffed. You don't even want to think about eating any more right now. Maybe in 4 or 5 hours time.



Hormones and the Hypothalamus

The hypothalamus is a small part of the brain, about the size of a pea, situatuated between the brain stem and the pituitary gland. Its function is to translate between the nervous and the endocrine system, and it regulates a lot of basic bodily functions, including hunger and satiety. It is divided into different areas, call "nuclei", which have distinct functions:



The ones we're most interested in are:

arcuate nucleus (AN) - Interface
lateral hypothalamic nucleus (LHN) - Hunger
ventromedial hypothalamic nucleus (VMHN) - Satiety
paraventricular hypothalamic nucleus (PVHN) - Interface


(source)

If we now look at the various hormones and neuropeptides in the bloodstream used as signals, we can see how they interact with each other and these nuclei:



Ghrelin - Grehlin regulates the appetite, and signals the need to eat again. When grehlin puts out its emptiness-type hunger signals, the wave-like peristaltic motion in the stomach (used to churn food up with the digestive juices and move it along the digestive tract) increases in intensity, becoming “hunger pangs.” Along with these hunger pangs, often comes a slight headache, mental fogginess and feelings of fatigue. When we feel these pains, we know for certain that we are hungry and it’s time to eat again. Another phenomenon that occurs when our stomach is empty, is a growling sound, which appears to indicate hunger. This “growling” happens when the stomach and/or intestines have become empty, and the gurgling sounds of ever-present peristalsis are no longer muffled by GI tract contents. This is why sometimes, even when we don’t feel hunger, our stomach still growls, as it is not always the stomach, but the intestines that are making the sounds.

Grehlin is released by the gastric glands in the fundus of the stomach when you start to eat. It can also be released by the (AN) when the body anticipates it is about to eat, or when it has hopes that a search for food might be productive and wants to motivate the person to change their current activity over to the pursuit and consumption of food.



Cholecystokinin (CCK) - Released by the duodenum (the first section of the small intentine, just below the stomach). It signals that it is time to pause eating, and acts via the (AN) to suppress hunger.



Pancreatic Peptide YY3-36 (PYY) - Released by the pancreas. It signals that it is time to pause eating, and acts via the (AN) to suppress hunger.



Melatonin - Released when it is dark. Put the body into its night-time state, of increased heat production and lowers appetite.



Agouti-related neuropeptide (AgRP) - Released by the (AN) as a means of turning off the satiety signals normally sent out by the (VMHN) and the (PVHN).



Neuropeptide Y (NPY) - Released by the (AN) as a means of turning off the satiety signals normally sent out by the (VMHN) and the (PVHN). It also seems to have an effect on insulin and glycogen levels (link).



Leptin - Leptin is released by adipose tissue. The more fat your body is storing, the higher the concentration of leptin in your bloodstream. This is received by the (AN) and influences the decision of when you've had enough to eat by reducing how much Neuropeptide Y is released.



Glucagon - Released by the pancreas, when the level of glucose in the bloodstream falls dangerously low. It triggers Glycogenolysis (turning glycogen into glucose) and, when the glycogen runs out, Gluconeogenesis (turning fats into glucose) and Lipolysis (turning fats into ketones) in the liver.



Insulin - When there are high levels of insulin in the bloodstream, the muscles and liver take glucose out of the bloodstream and store it as glycogen. Proteolysis (turning protein into energy) is inhibited, as is the release of Glucagon. It also causes any excess glucose in the bloodstream to be stored in the adipose tissue, where it eventually gets laid down as fat if not used up. When there are low levels of insulin in the bloodstream, the muscles and liver convert the glycogen they have stored and release it into the bloodstream as glucose.

Insulin is release by the beta cells in the islets of Langerhans in the pancreas, but what triggers this is a bit complex. High levels of glucose in the blood. Various digestion by-products that indicate to the pancreas that there will be high levels of glucose in the blood in a little while once the food currently in the stomach slips down into the small intestine. Stress. Adrenaline. Signals from the vagus nerve. Various drugs, like clonidine. This can all happen very fast - insulin levels can rise, trigger the absorption of glucose, crash and thereby trigger the re-emission of glucose, all in a period of 6 minutes or less.

And, of course, it is a major input (along with the glucose levels) to the (AN). High levels of insulin lead to hunger because they are saying "We anticipate receiving food shortly, so are clearing out glucose in anticipation of you providing us with more."





There are many more hormones that are involved, but that will do for now. Let's finish with the other effects of the hypothalamus connected with hunger.

The lateral hypothalamus (LHN) makes food seem tastier, tells the cerebral cortex to motivate you to look for food, triggers release of saliva and digestive hormones, and signals the pancreas to release more insulin.



(source)

The paraventrical hypothalamus (PVHN) is the source of craving-type hunger. It interfaces with learned responses, and specific nutritional deficits in your body to decide (for example) that during pregnancy that what you really really need is marmite flavoured ice cream with sardines. Or crunchy bits of bacon. Or chocolate, lovely smooth warm melt-in-the-mouth chocolate. That's the PVHN talking.



Summary so far

Part 1 - how many kilocalories to eat

Part 2 - what motivates us to eat or not eat

This leaves two unanswered questions:

a) what's the optimal way to divide your daily kilocalorie budget in order to minimise hunger. How much should you eat, at what times of day, and of what types of food?

b) what does psychology tell us about other things we can do, in practice, both to reduce hunger and to deal with the other motivations that affect eating? How can we deal with hunger? How can we resist it?
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So far I've not said anything controversial. But, if the science is so straightforwards, why are there so many different theories on how to diet, and why do people find it so difficult?

So I want to talking in this part about sources of error and uncertainty, and how we know what we know.

Losing 1 pound of weight per week sounds like it ought to be easy to measure. After all, we can build kitchen scales that can measure weight down to a single ounce. But 1 pound per week is just 0.2 pounds per day. Now compare that to how much goes in and out of the human body each day:

Image

Even if you weigh yourself each day at the same time, before breakfast but after going to the toilet, naked to avoid variation in clothing, there is still a daily variation of about plus or minus 2 pounds, just from your hydration level.

So it is quite difficult to get immediate feedback on how well something is working. You can't spot an increase and attribute precisely that weight gain to a burger you ate the day before. To get a clear view, you have to look at the average of all the weighings during a week, and compare that with the average from previous weeks, which can turn a graph like:

Image



into a much clearer picture:

Image

(source)



There's also more uncertainty that you'd think on the other side of the equation - recording what we eat.

A study was carried out whereby a group of people were asked to record the kilocalories they consumed and the exercise they took, and weigh themselves daily. The scientists were surprised to discover that many people were reporting weight gain that couldn't be explained by the difference between the kilocalories they reported consuming and the kilocalories burnt. So they repeated the experiment, this time doing it in a closed environment where the only food available was stuff visible on-camera, and the scientists recorded how much the subjects ate.

What they discovered was that people are very bad at noticing when they are eating, especially if there are snacks around. They deceive themselves, telling themselves "It is just one biscuit, it isn't a meal so it doesn't count, I don't have to write it down", but not noticing that they consumed 20 biscuits during the day.



And the human body isn't in a much better situation. It doesn't have a bomb calorimeter that measures the precise kilocalorie value of everything eaten. It doesn't have a pair of scales built into the feet that say exactly how much you weigh.

We've seen, from looking at the web of hormones, what sort of things the body does measure. It measures how full and how active the stomach and duodenum are. It measures the levels of glucose and lipids in the bloodstream. It has an indirect measure of how much total fat the body is storing, from the leptin levels. And it gets warned when the liver and muscles are low on stored glycogen.

It also has, as an input, learned reactions from the mind. It can anticipate roughly how full it is going to be from eating a particular meal, based on the person's previous experiences and expectations, and what they can see, smell and taste.



Scientists discover a lot of what they know about how healthy bodies use these inputs to regulate hunger and stored fat by looking at individuals who are abnormal in some way. Individuals who've had part of their brain damaged, or who have abnormally high or low levels of a particular hormone or chemical, or who've had parts of their stomach removed or who were born with a genetic abnormality.



lateral hypothalamic nucleus (LHN) - When the (LHN) in humans is damaged, by a lesion growing upon it, the person feels no motivation to start eating and drinking. It controls insulin secretion and alters taste responsiveness. Animals with damage to this area refuse food and water and may starve to death unless force fed.

paraventricular hypothalamic nucleus (PVHN) - When the paraventricular nucleus of a rat is damaged, the rat will eat a very large quantity of food at each meal.

ventromedial hypothalamic nucleus (VMHN) - If we inject a neurotoxin (such as gold thioglucose) into the (VMHN) of mice, the mice overeat and became very fat.

When the (VMHN) in humans is damaged, by a lesion growing upon it, we also observe increased levels of insulin in the bloodstream. However later research showed that it is possible that the lesion was also affecting the (PVHN) and (LHN).

Damage to the (VMHN) in humans also causes the stomach to empty faster than usual (due to increased stomach secretions and motility), and such people tend to each normal sized but unusually frequent meals.

Prader–Willi syndrome is a genetic abnormality on chromosome 15. Individuals suffering from it display an extreme and insatiable appetite (among other symptoms), and are generally morbidly obese if they survive to adulthood. They have 5 times the normal amount of ghrelin in their bloodstream.

Similar monogenic human obesity syndromes have helped identify the roles of leptin and melanocortin.

In mice, the administration of leptin to leptin-deficient ob/ob mice results in weight loss and decrease in food intake. Otherwise these mice exhibit rapid weight gain in the first few months of life and aggressive behaviour when denied food. Humans with this condition exhibit an intense drive to eat that is never satisfied.

(source) (source) (source) (source) (source) (source)



One last source of variation, and that's the weight loss plateau. The short term speed of human metabolism is controlled by the thyroid gland, which releases thyroxine and tri-iodothyronin. Too little, and you suffer from hypothyroidism. The body conserves energy by stopping all repairs (so injuries take longer to heal, and arthritis builds up), all growth and cell replacement (leading to anaemia and the build up of toxins), the circulation slows down (often causing headaches), the fertility and immune systems go on strike (leading to infertility and diseases) and you are less active (because of fatigue). Too much, and you suffer from hyperthyroidism. Symptoms include nervousness, irritability, increased perspiration, heart racing, hand tremors, anxiety, difficulty sleeping, thinning of the skin, fine brittle hair, muscular weakness and more frequent bowel movements. Your whole body, and all the processes in it, speed up. You burn energy like there's no tomorrow. (In case you think body repair isn't a significant factor, bear in mind that patients in hospital with severe burns can use up 8000 kilocalories a day just lying there. I wouldn't recommend it as a diet method though.)

These are called hypothyroidism and hyperthyroidism if it is a long term pattern. In the short term, these are actually a natural ability of the body, used to regulate how much energy it expends. It can't change the long term average without causing problems, but in the short term (a few days) it can balance out, putting things off or bringing things forwards. This means that, if you drastically reduce how much energy you are taking in, the body tends to respond by trying to reduce how much energy it puts out, to compensate. It can only compensate for small amounts in the long term but, in the short term dieters often see a small weight loss then a plateau where they're doing everything right but their weight stubbornly refuses to decrease.

Another problem of starvation diets is that it tells the body that the food supply is not reliable, and that it needs to set its 'set point' at a higher level, in order to provide a bigger safety net.

Have a read of this page: FOOD AND FEEDBACK.

It explains the terminology "positive feedback loop" and "negative feedback loop" that we're going to use in our next section, where we consider specific diets and how they are claimed to work.

Don't worry if it is a little too technical. The main thing to take away is that while the system controlling how hungry or satiated we are is complex and may have a wide range of genetic difference in it between people (what weight your body is trying to motivate you to be, and how it responds to variation away from that weight), this is all about motivation. Your genes can't actually force you to eat too much if you choose not to. It doesn't magically create calories from thin air. If someone with Prader-Willi syndrome can lose weight on a calorie controlled diet, then you can too.

The human body is generally a very efficient machine. When it expends energy, it does so by doing something. So, someone who is 'naturally thin' gets that way because either their body does something extra (like running a higher body temperature, or fidgeting tappign their feet constantly even while sitting at a desk) or it eats fewer calories. Someone who is 'naturally fat' gets that way because either their body does something less (maybe they expend less energy on their immune system, or they tend to sit immobile with a low heart rate) or it eats a greater number of calories. If you change what you do and what you eat, you change your weight. It isn't just simple; it is an inevitable consequence of the laws of physics, chemistry and biology.

But I asked "why do people find it so difficult?". Why, if it is that simple, do so many people not just use 'willpower' to attain the weight they wish? Well, simple is not the same as easy. Bear in mind that eating is a life-or-death issue. Evolution has strongly selected against people who found it too easy to over-ride the hunger motivating them to eat. It is possible though, because evolution also selected against hungry people who left the cave in the middle of the night to find strawberries for a late night snack, and got eaten by a saber-toothed tiger.

Part of the answer is that psychology can be used to change how much willpower is required. And really that's what dieting is all about. It is using tools and practices that affect what, when and how we eat in order to alter our 'natural' hunger level by bringing other motivations into play and 'gaming the system'. In short, human biology is imperfect. It is adapted to a particular environment and we can take advantage of that to cheat - to fool the tools it uses to try to direct our weight and eating levels in the direction it thinks we need to go.

People vary in how their bodies works - which bits of their metabolisms are more efficient than others. Therefore some diets may work better for some people than others. Especially in the mental aspect, since people's minds vary far more than their metabolisms do.

In the next section I'm going to look at specific diets. How they are claimed to work, and their pros and cons. But bear in mind that all diets that control calorie intake and expenditure will 'work' in that they can produce weight loss. Where they vary is in their other effects - how healthy they are for you, how much effective energy you have to do stuff while on them, how much willpower people with different mind-types need to follow them strictly, whether they make a long-term change in your lifestyle, or if you return to your previous weight within a year.

As I've listed in this journal part, there are several sources of uncertainty, both in measuring the inputs and effects of a diet, and in how the underlying biology works. This has led to a proliferation of pseudo-science. Because almost anything will 'work', as long as it forces you to pay attention to something that affects how many calories you take in (such as specifying portion sizes, or food types, or food volume). And, if someone has faith in the effectiveness of a particular diet, that helps their motivation to stick to it, thus (for them) making it more effective. When you throw in the fact that diet books, videos and organisations are a very big business, with a lot of money at stake, you can see why it is in the interests of diet authors to look only for research that confirms their particular findings, and not to care if that research is outdated. The more research they can list, the easier it is for a follower to convince themselves that their author knows the One True Way of Dieting. And, humans being what they are, many of those followers then become True Believers, castigating anyone who disagrees with the conclusions of their guru.

So, in the next part, I'll try to separate out individual claims, to distinguish between the bits of advice or theory that have a balanced scientific basis, and those which work only incidentally.
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There are many weight-loss diets out there:

WikiPedia listing of diets
WebMD listing of diets


To make things easier for myself, I'm going to assume that the people reading this journal are chiefly interested in long-term sustainable loss of significant amounts of weight, rather than losing a couple of pounds quickly to look good in a bikini for the summer. And I'm initially going to look at the core mechanisms of the diets - how they say that the type and timing of food intake and exercise affects short term and long term hunger, energy in and energy out. I'll leave stuff specific to the start of a diet (jump starting) or end of a diet (moving from weekly weight loss to a weekly steady weight) to later, except to note that if you have previously been someone who easily gained weight or found it hard to maintain a steady weight, a diet doesn't have an effect beyond 12 months unless it goes hand in hand with a change in lifestyle or habits. I'll also leave to later questions of surgery and medicines that affect metabolism, motivation and digestion.



Diet Name : Volumetrics
Core Claim : You feel full when your stomach is physically full
Advice : Eat food that has a low energy density (kilocalories per volume, or kilocalories per mass)
Originator : Barbara J. Rolls
Scientific Credentials : Professor of Nutrition at Penn State University
Links: eHow, LiveStrong, WiseGeek, Xomba, MedicineNet,

Densities :

Kcal/g g/cm3 Kcal/cm3

Fat 9 1.1 9.9
Alcohol 7 0.8 5.6
Protein 4 1.3 5.2
Carbohydrate 4 1.5 6.0
Fibre 2 0.9 1.8
Water 0 1.0 0.0

The diet recommends drinking a lot of water (10 six-ounce glasses per day) and soups, and going for fruit and vegetables that are high in water and fibre.

On the question of whether you should get your calories via fats, proteins or carbohydrates, the diet is neutral except in as far as they have different kilocalories per volume, but notes that you need nutrients to avoid ill-health and craving-type hunger, and that high fat foods are generally low on nutrients. Barbara Rolls suggests an approximate aim of: 20% fats, 30% proteins, 50% carbohydrates.

Research :

Rolls, B.J. (2009). The relationship between dietary energy density and energy intake. Physiology & Behavior, 97:609-615. (link)
Basis of the diet

Hetherington, M.M. and Rolls, B.J. (2008) From protocols to populations: establishing a role for energy density of food in the obesity epidemic. In: Obesity: Causes, Mechanisms, Prevention, and Treatment. Ed. E.M. Blass. Sinauer Associates, Inc. Publishers, Sunderland, MA, pp. 301-318.
Basis of the diet

Kirkmeyer, S.V. and Mattes, R.D.[2000] "Effects of food attributes on hunger and food intake" International Journal of Obesity, September 2000, Volume 24, Number 9, Pages 1167-1175 (link)
Results: on a 3 hour timespan, the kilocalories in a meal are more important to how satiated it makes you feel, than its mass or volume. In a shorter timespan (ie when deciding to stop eating the meal), mass is generally more important than volume, as the volume capacity of the stomach is rarely reached and the work the digestive system will have to do is proportionate to mass not volume. It also linked to research showing that solids were more effective at generating satiety than liquids.

1. Experiments in which a balloon was swallowed suggested that the contraction of the stomach caused the "pangs of hunger"

These observations led to the idea that hunger is caused by stomach contractions, and satiety is produced by stomach distention.

-However, cutting the nervous connection of the stomach did not change the ingestive behavior.

-Also, ablation of the stomach did not prevent the feelings of hunger and satiety, although the patients ate more frequent and smaller meals.

2. Food maintained in a transplanted stomach by a noose in the pyloric sphincter was able to decrease eating in proportion to its caloric content and volume.

Since the transplant had no innervation, and no food is absorved by the stomach, the signals had to be chemicals produced by the stomach.

(source)

Cannon and Washburn (as cited in Coon, 1995) came up with the stomach contraction theory which states that we know we are hungry when our stomach contracts. In the notorious balloon study, Washburn trained himself to swallow a balloon which was attached to a tube, then the balloon was inflated inside of his stomach. When the balloon was inflated, he did not feel hungry. Later this theory was opposed by the fact that people whose stomach was removed still felt hungry. Glucose theory states that we feel hungry when our blood glucose level is low. Bash (as cited in Franken, 1994) conducted an experiment transfusing blood from a satiated dog to a starved dog. The transfusion resulted in termination of stomach contraction in the starved dog, and supported the glucose theory. But as LeMagnen (as cited in Kalat, 1995) suggests that blood glucose level does not change much under normal conditions. Insulin theory states that we feel hungry when our insulin level increases suddenly in our bodies (Heller, & Heller, 1991). However, this theory seems to indicate that we have to eat to increase our insulin level in order to feel hungry. Fatty acid theory states that our bodies have receptors that detect an increase in the level of fatty acid. Activation of the receptor for fatty acid triggers hunger (Dole, 1956, Klein et al., 1960 cited in Franken, 1994). Heat-Production theory suggested by Brobeck (as cited in Franken, 1994) states that we feel hungry when our body temperature drops, and when it rises, the hunger decreases. This might be explain that we tend to eat more during winter. (source)

Coon, D. (1995). Introduction to Psychology: Exploration and Application, 7th ed. MN:West Publishing Company.
Franken, R. E. (1994). Human Motivation, 3rd ed. CA: Brooks/Cole Publishing Company.
Heller, R. F., & Heller, R. F. (1991). The Carbohydrate Addict's Diet. New York: Penguin Books USA Inc.
Kalat, J. W. (1995). Biological Psychology, 5th ed. CA: Brooks/Cole Publishing Company.


Clairwil's Conclusion on Volumetrics :

The research seems pretty solid that mass of food consumed (or volume, which correlates with mass), is one cue that the body uses for short term satiety, to decide when to stop eating during a particular meal. It isn't the only cue, and doesn't have an effect lasting more than a few hours, so it can help, but only if the total number of meals and snacking are strictly controlled.



===================

Ok, enough Volumetrics, next diet:

Diet Name : Set Point Theory
Core Claim 1 : Your body has a thermostat-like control that manipulates your hunger and metabolism with the objective of returning your weight to a particular set level. The lower you go beneath this, the hungrier you'll get.
Core Claim 2 : This set point change be slowly changed in the long term, by sticking to a diet & exercise regime
Advice : Go steady, avoid triggering the starvation reflex, exercise
Originators : William Bennett and Joel Gurin
Scientific Credentials : Bennett was a doctor
Links: MIT Medical, WeightLossForAll, WiseGeek, About.Com, DietChannel,

Research :

Dieter's Dilemma: Eating Less and Weighing More (link)
The book the diet is based upon.

Wilmore et al, "Alterations in resting metabolic rate as a consequence of 20 wk of endurance training: the HERITAGE Family Study" American Journal of Clinical Nutrition (link)
Aerobic endurance exercise doesn't boost the basal metabolic rate

Hill A.J. [2007] "The psychology of food craving" Proc Nutr Soc. 2007 May;66(2):277-85. (link)
Food cravings are influenced by learned information, such as cultural expectations, and are based upon the mind's predictions of scarcity and future availability, not just on the body's information about current deficits.

Bodenlos et al [2007] "Vagus nerve stimulation acutely alters food craving in adults with depression", Science Direct (link)
Set point is affected by the mind (for example, by depression)



Clairwil's Conclusion on Set Point Theory :

While leptin does provide a biological input telling the brain how much fat there is in the body, it seems likely that, to the extent there is a set point at all, it is mental rather than biologically and genetically pre-determined, and that the original observations which triggered this idea can be explained by a combination of the short-term plateau effect and the longer term changes to the basal metabolic rate than can be achieved by increasing muscle mass. That said, just because something is mental it doesn't mean it isn't a real effect. This explains nicely the mechanism by which a mental expectation of a cold winter or famine can lead to higher body mass. And it emphasises the importance of believing that the 'real you' is a lower weight, and seing you current high weight as an abnormality, rather than seing you current state as being your identity and some future 'thin self' as a fantasy. The reason behind you getting hungrier, the lower your weight, has I think to do with getting used to smaller portion sizes (because large people burn more energy just walking around, they can get the same weekly weight loss while eating more. as you lose weight, to keep the same rate of weight loss you need to eat less). However that's my personal guess, not backed by any evidence.



===================

Next diet:

Diet Name : Government Approved Diets (Food Pyramid - USA, Food Plate - UK)
Core Claim 1 : Items of food can be classied into "Food Group"
Core Claim 2 : You can control the proportions of fat:carbohydrate:protein you take in by controlling the balance of the amount of food items you eat from each food group
Core Claim 3 : Your body's nutritional needs are best met by eating a balanced diet
Core Claim 4 : Don't eat too many saturated fats
Scientific Credentials : entire government health departments
Links: UK Gov : Balanced Diet, UK Gov : Lose Weight, USA Gov : Balanced Diet, USA Gov : Lose Weight, data1, data2

This isn't so much a weight loss diet, as a healthy eating diet. However both government websites do have sections aimed at those intending to lose weight. And it is a good starting point, not only because of the enormous weight of research behind it, but because many of the core claims are disputed by 'fad' diets.

Advice :





How to have a healthy balanced diet
● Base meals on starchy foods such as potatoes, bread, rice and pasta, choosing wholegrain
where possible.
● Eat plenty of fibre-rich foods – such as oats, beans, peas, lentils, grains, seeds, fruit and
vegetables, as well as wholegrain bread, brown rice and pasta.
● Eat at least five portions of fruit and vegetables a day in place of foods higher in fat and calories.
● Eat a low-fat diet, and avoid increasing your fat and/or calorie intake.
● Eat as little as possible of: fried foods; drinks and confectionery high in added sugars; and other
food and drinks high in fat and sugar, such as some take away and fast foods.
● Eat breakfast.
● Watch the portion size of meals and snacks, and how often you are eating.
● Avoid taking in too many calories in the form of alcohol. (source)

Different types of diet
● For sustainable weight loss, recommend diets that have a 600 kcal/day deficit (that is, they contain
600 kcal less than the person needs to stay the same weight) or that reduce calories by lowering the
fat content (low-fat diets), in combination with expert support and intensive follow-up.
● Low-calorie diets (1000–1600 kcal/day) may also be considered, but are less likely to be nutritionally
complete.
● Very-low-calorie diets (less than 1000 kcal/day) may be used for a maximum of 12 weeks
continuously, or intermittently with a low-calorie diet (for example for 2–4 days a week), if the
person is obese and has reached a plateau in weight loss.
● Any diet of less than 600kcal/day should be used only under clinical supervision.



I've given the advice from two different governments because of conspiracy theorists who don't trust their own government, but you can go to practically any government health department or university nutrition department in the world and get practically identical advice.

The advice isn't very popular with consumers, both because it is pretty prescriptive, and because it advises 30 minutes of exercise that gets you to feel warm and slightly out of breath, at least 5 times a week.



The advice on not having too much meat is, by the way, not because protein is particular bad, but because the foods that carry protein generally also carry fat. The fat in food items can be categorised into four types:
* saturated fats (the sort you get in meat, milk, cheese and butter)
* non-trans mono-unsaturated fats (the sort you get in things like olive oil and avacado oil)
* non-trans poly-unsaturated fats (the sort you get in sunflower oil and sea fish)
* trans unsaturated fats (the sort you get from the partially hydrogenated oils in fast food)

Saturated fats lead to cholesterol, which leads to heart attacks. Since that is a contested claim, I need to go into a bit more detail.

Cholesterol is needed by the body, which uses it to construct various cell structures and hormones. We take in a small amount of cholesterol in our diet but the majority of the cholesterol isn't eaten - it is created by the liver while digesting saturated fats. Fat isn't soluble in water so it is carried around the body in the bloodstream inside 5 different types of lipoprotein particles:
1. Chylomicrons (CM) - used to move fat and cholesterol from the intestine to the liver, where the fat is converted into cholesterol and triglycerides (the form of fat the body prefers to have it in)
2. Very Low Density Lipoproteins (VLDL) - used to move triglycerides from the liver to the muscles and adipose tissue
3. Intermediate Density Lipoproteins (IDL)
4. Low Density Lipoproteins (LDL) - used to carry cholesterol from the liver to the cells of the body
5. High Density Lipoproteins (HDL) - used to carry cholesterol from the cells of the body back to the liver where it is dumped out into the bile

In fact many of these are not really different types of particle, they are just classified by how much of which sort of thing they are carrying. IDL is just the name given to the particle when it is on its way back from the muscles to the liver, characterised by how much fat and cholesterol it tends to be carrying on that stage of its journey. LDLs are thought of as 'nasty' because, if you have too many in the blood the tissue can't accept cholesterol at such a fast rate and the excess gets dumped in the arteries where it causes Atherosclerosis which leads to heart attacks. Doctors will talk to you about the ratio of LDLs to HDLs in your blood test result, but the LDLs are not the cause of the excess cholesterol - they're a symptom. What actually needs to be reduced is the amount of cholesterol that is produced by the liver but not used in cells, and that means cutting down the amount of saturated fats consumed. (There are other factors, such as stress, smoking and oxidising agents, but the amount of saturated fats is the main factor.)

Trans-fats, by the way, seem to have the same effect upon cholesterol as saturated fats do.

Sources: Fats 101, About.Com, "Understanding Cholesterol" by Dr. Mike Laker published by the British Medical Association



Research :

It is surprisingly difficult to trace back the government advice to specific research papers.

The closest I can find is the list of research given in NICE's Management of obesity document.

However here are a couple of pages discussing government versus fad diets:

Is the Diet Advice from the Government Big Fat Lies?

The truth about fad diets



Clairwil's Conclusion on Government Diets :

I said in an earlier part of this journal that weight loss depends upon consuming fewer calories than you burn, and diet is about psychology - managing willpower, habit and hunger to make it easier for you to do this.

So it is possible for the advice the government gives about the WAY you should approach measuring things, eating the correct amount and sticking to it to be very ineffective psychology for some people while, at the same time, the advice it gives on WHAT you ought to end up eating being very well founded.

The main accusation against the government advice is that it doesn't work. Somewhere between 60% and 90% of dieters fail to achieve their long term goals. I don't know how the government diet compares with other diets - I can't find statistics on that. But that's the accusation levelled against it. And often the accusation is couple with the inference that the reason why it doesn't work is not poor psychology or the intrinsic difficulty in motivating people to diet, but because the advice on what to eat is incorrect. That people ought to end up consuming a different proportion of fats : protein : carbohydrates in order to lose weight.
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Although the amount of weight you lose depends on how many calories you take in, and how many you burn, many diets suggest what fraction of your daily calories taken in you ought to get from fats, proteins and carbohydrates. Most do this because of nutritional requirements or factors not related to weight loss (such as the chances of dying from a heart attack), but some make claims relating the proportions to how hungry you get, how your 'set point' changes over the long term, the proportion of fat to muscle in your body, how much energy your digestive system burns and your basal metabolic rate. It is these claims that I'd like to look at in this part.

These diets can be divided into:

* High Fat - Low Carbohydrate
* High Fat - Low Protein
* High Carbohydrate - Low Protein
* High Carbohydrate - Low Fat
* High Protein - Low Carbohydrate
* High Protein - Low Fat




For reference, here are the government recommended maximum and minimum daily amounts (for a woman), in grams:

Minimum Maximum
Fats : 14 65
Poly Unsaturated 14
Saturated 20
Carbohydrates : 130 300
Proteins : 46
Fibre : 25
Water : 2700

(source) (source)

===================

Diet : High Fat - Low Carbohydrate
Claim 1 : High sugar levels in your bloodstream are bad for you
Claim 2 : Carbohydrates cause cholesterol
Claim 3 : Carbohydrates cause hunger
Claim 4 : The key to reducing body fat is ketogenesis
Claim 5 : Ketogenesis only happens when you have low carbohydrates

Image

(MCT = Medium-chain triglycerides)



Sources of claims :

Blood sugar levels of over 140 miligrams per decilitre cause organ damage
(source)

It is the carbohydrates you eat that raise your blood sugar. If you cut back on carbohydrates, your blood sugar will come down. It's that simple. Solid research has proven that it is not eating fats that raise cholesterol, either, but eating carbohydrates which convert into dangerous triglycerides. So while it is true that eating fats along with carbohydrates is very unhealthy, the less carbohydrate you eat, the more fat you can eat safely.
(source)

The bad feeling comes from having a lot of insulin and very little glucose in your blood. Insulin levels go up after you eat carbohydrates, and stay up after the carbohydrates are consumed. This is what makes you feel hungry a few hours after a big meal. The bad feeling will eventually go away, and as long as you don't hit the carbs, it will stay away. Most fat people have high levels of insulin most of the time because at any given time they will have eaten lots of carbohydrates not too long ago. And they keep hitting the carbs, so the insulin never drops.
Once you have emptied out the glucose and glycogen, your body will start turning fat into energy. Your body still needs a little bit of glucose, but it can synthesize this glucose from protein, and then it will only make as much as it needs. This is why you have to eat meat.
People often say, with a hint of scorn, "everybody knows that to lose weight, you just have to burn more calories than you consume." This is true, but there are two ways to do it: exercise more, or eat less. Because eating less is considered beyond mortal abilities, gyms have flourished. Why is it beyond mortal abilities? If you're still eating carbohydrates every day, only "less", your body will make you feel terrible every day, because of the insulin reaction. And you will have to spend a lot of time at the gym to use up the carbohydrates you did eat before they turn into fat.
You should be eating more meat than cheese. If you eat too much cheese, your body will use dietary fat, not body fat.
But some amount of fats are very helpful. Fats make you feel full so you stop eating sooner. In fact, people who can't lose weight any other way are put on the Fat Fast: mayonnaise, bacon, pate, tuna salad. And yes, they lose weight.
(source)

insulin resistance is a prime factor that leads to raging hunger.

Exactly why isn't completely understood, but we do know that one of the main things that can cause hunger is swiftly moving blood sugar of the type that happen when blood sugar goes way up after a meal and then plummets back down as it does in hypoglyemica.
(source)

Glucose, also called blood sugar, is the main fuel your brain, heart & muscles use for energy. Without adequate amounts of glucose your brain does not think clearly and in extreme cases people can fall into a coma. Glucose at elevated levels is also not good. In medicine elevated glucose levels is called diabetes, and creates problems when uncontrolled to the eyes, nerves, kidneys, heart and other parts of the body.

Insulin decreases glucose levels and therefore protects against the damage glucose can create. Unfortunately having an excess of insulin on an ongoing basis in the bloodstream creates chronic inflammation and increased fat storage.

When glucose and insulin work together they create a rollercoaster effect insulin always chasing glucose to try and control it (see chart 1). As glucose goes below 70-80 hunger becomes strong. And most commonly we reach for some type of simple carbohydrate (candy, chocolate, pastry) to quench that hunger.

Image

(source)

Eating Too Many High GI Carbs Causes Sugar Spike

The hunger-or-insulin see-saw mechanism works well, provided that we don't eat too many high glycemic index (GI) carbs that are rapidly converted into glucose. When this happens, when a LARGE amount of glucose enters the bloodstream (called a "sugar spike"), the system responds by releasing a LARGE quantity of insulin. (It thinks we've eaten a huge amount of food.) The amount of insulin is so large that not only does it disperse the food-glucose we have just eaten, it disperses a lot more. Result? Our blood glucose falls too low. So, within a short time (about 2-3 hours) the brain tells us to feel hungry and we recommence eating. This rapid rise and fall in blood glucose, caused by excess production of insulin, is not good for our health or our eating habits.
(source)



Not all High Fat - Low Carbohydrate make all of the claims, but a variety of named diets based upon some or all of the above principles are:

* Atkins Diet
* Ketogenic Diet
* No-Carbohydrate Diet
* Low-Glycemic-Index Diet
* Gary Taubes Diet

Links to further information:

Glycemic Index, from WebMD
Glycemic Index, from WikiPedia
Insulin Index
The Way We Eat Now
Insulin Response to Sight and Smell of Sweet Foods
Causes of Diabetes





Related Research:

A) Higher the carbohydrate, the greater the leptin activation
Yannakoulia M, Yiannakouris N, Bluher S, Matalas AL, Klimis-Zacas D, Mantzoros CS [2003] "Body fat mass and macronutrient intake in relation to circulating soluble leptin receptor, free leptin index, adiponectin, and resistin concentrations in healthy humans." J Clin Endocrinol Metab. 2003 Apr;88(4):1730-6.
B) Higher glycemic index eating causes increased triglycerides
Pawlak DB, Kushner JA, Ludwig DS. [2004] "Effects of dietary glycaemic index on adiposity, glucose homoeostasis, and plasma lipids in animals." Lancet. 2004 Aug 28;364(9436):778-85.
C) Higher glycemic index eating causes increased insulin resistance
Brynes AE, Mark Edwards C, Ghatei MA, Dornhorst A, Morgan LM, Bloom SR, Frost GS. [2003] "A randomised four-intervention crossover study investigating the effect of carbohydrates on daytime profiles of insulin, glucose, non-esterified fatty acids and triacylglycerols in middle-aged men." Br J Nutr. 2003 Feb;89(2):207-18.
(source)

Holt, S.H. ;Miller, J.C. and Petocz, P. [1997] "An insulin index of foods: the insulin demand generated by 1000-kJ portions of common foods", Am J Clin Nutr 1997 66: 1264-1276 Am J Clin Nutr free full text PDF

Johnston, Carol S.; Tjonn, Sherrie L.; Swan, Pamela D.; White, Andrea; Hutchins, Heather; Sears, Barry [2006] "Ketogenic low-carbohydrate diets have no metabolic advantage over nonketogenic low-carbohydrate diets" American Journal of Clinical Nutrition, Vol. 83, No. 5, 1055-1061, May 2006 (link)
We compared weight loss and biomarker change in adults adhering to a ketogenic low-carbohydrate (KLC) diet or a nonketogenic low-carbohydrate (NLC) diet. KLC and NLC diets were equally effective in reducing body weight and insulin resistance, but the KLC diet was associated with several adverse metabolic and emotional effects. The use of ketogenic diets for weight loss is not warranted.



A) Leptin-Taste System
Shigemura N, Ohta R, Kusakabe Y, Miura H, Hino A, Koyano K, Nakashima K, Ninomiya Y. Leptin modulates behavioral responses to sweet substances by influencing peripheral taste structures. Endocrinology. 2004 Feb;145(2):839-47. Epub 2003 Oct 30.
B) Sugar or drug rewards enforce addictive conditioning
Di Ciano P, Everitt BJ. Conditioned reinforcing properties of stimuli paired with self-administered cocaine, heroin or sucrose: implications for the persistence of addictive behaviour. Neuropharmacology. 2004;47 Suppl 1:202-13.
C) Learned addiction
Wang GJ, Volkow ND, Thanos PK, Fowler JS. Similarity between obesity and drug addiction as assessed by neurofunctional imaging: a concept review. J Addict Dis. 2004;23(3):39-53.
(source)


There is much more research listed at the wikipedia entry:
Medical research related to low-carbohydrate diets



Clairwil's Conclusion on High Fat - Low Carbohydrate diets :

Mostly a load of bunkum...

Onset of type II Diabetes is correlated with obesity, but not with carbohydrate intake (except in as far as an uncontrolled diet high in carbohydrates tends to lead to obesity).

High bloodstream glucose levels can cause organ damage (as they do in untreated diabetes), but this doesn't mean that you need to eat very low levels of carbohydrates in your diet in order to be safe (unless, perhaps, you are already diabetic).

Change of insulin levels are one (of a number) of hunger cues, but they are not solely caused by what you eat. They can also be caused by your body anticipating what you're about to eat by, for example, your seeing a picture of something tasty on television.

Glycemic index depends on a number of factors, including:
* the type of starch (amylose versus amylopectin)
* physical entrapment of the starch molecules within the food
* fat and protein content of the food
* organic acids or their salts in the meal — adding vinegar, for example, will lower the GI.
* The presence of fat or soluble dietary fiber can slow the gastric emptying rate, thus lowering the GI.
and, in general, doesn't seem to have a high correlation with the hunger suppression per calorie rating of a food item. It is a factor, but not the only one, and the insulin index seems a better measure of it. (see links)

The claim that the body has to burn more calories to metabolise fat than it has to in order to metabolise carbohydrate isn't a large factor, and protein takes even more energy to digest than either.

The claim that you, long term, need to eat low carbohydrates in order to get reduction in body fat is just plain incorrect.

The claim about cholesterol not being increased by saturated fat intake is also just plain wrong.



Summary : Other factors being equal, you may see some benefit in reducing hunger by picking your carbohydrates from low GI sources rather than high GI sources. But, while any diet that reduces your calorie intake below your calorie output will result in weight loss, if you choose a high fat - low carbohydrate diet with which to do so, you face a significant chance of severe health side effects. Don't do it.
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===================

Diet : F-Plan
Claim : Eat lots of fibre
Author : Audrey Eyton
Credentials : Journalist
Links: WikiPedia, High Fibre Diets under the Spotlight

Basically a corollary of volumetrics.



===================

Diet : The 10% Solution For A Healthy Life
Claim : Very low fat (10% maximum) is achievable and preferable to 30%.
Author : Ray Kurzweil
Credentials : Computer Scientist
Links: the complete text of the book, free from Ray's own website
More about longevity, cancer and heart disease than about weight loss.



===================

Diet : The Pritikin Program for Diet and Exercise
Advice : Go for unprocessed or minimally processed straight-from-nature foods
Author : Nathan Pritikin
Credentials : Nutritionist


A combination of volumetrics and glycemic index.



===================

Diet : Cookie Diets
Advice : Replace breakfast and lunch with set number of portion controlled snacks
Links: Smart for Life
Author : Sasson Moulavi
Credentials : Doctor


The cookies, despite the name, don't have an excessive amount of carbohydrates. They have a good amount of protein and are low on saturated fats. They're pretty balanced - it is a psychological way of doing portion control.



===================

Diet : The Cambridge Diet
Advice : Very low calorie liquid diet, designed for balance nutrition
Links: Wikipedia
Author : Alan Howard
Credentials : Professor at Cambridge University - medical research scientist


If you're going to have only 500 calories a day, this is the sort of thing you need, but really it should be done under medical supervision, and there is no evidence that it is easier to stick to or leads to a long term change in lifestyle. For immediate drastic weightloss.



===================
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:ugeek:
That's a whole lot of information.
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eyes4ears wrote: Thu May 24, 2018 9:19 pm :ugeek:
That's a whole lot of information.
I couldn’t read it all. I’m 33 lbs down tho. My formula is simple. Burn more calories than I take in. 1200 calories a day I eat. I burn around 300 extra in exercise along with what I normally do. I’ve been losing 1-2 lbs a week. It works for me.

I don’t know about any of that stuff lol
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One thing that stuck with me is that we don't keep gaining and losing the same 10 pounds. We regain more fat than muscle. Also, our body composition changes as we age, so we can weigh the same but look different because fat takes up more space. :(

What works for me:
FitBit -- movement reminders every hour, small goal of 6,000 steps a day and large goal of 10,000.
Treadmill -- 30 minutes a day, 2.5 to 3 mile pace which I can maintain while reading/playing on iPad
Weighing daily -- this is supposed to be bad, but it helps me not overeat
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