ã Todd I. Stark, 1998, all rights reserved.
In the first part, we will examine the theory. We will look at the scientific research behind body fat regulation, and see the strengths and weaknesses of the set-point concept. In the second part, we will examine the practical advice suggested by the theory, how we permanently change our body fat set-point.
You've probably heard about the concept that the body aggressively hangs on to its stores of body fat. This is often claimed to be the reason why people find it so hard to lose body fat permanently. In the most extreme version of the "body fat set-point theory," our genes supposedly predispose us to be lean or fat for our entire lives. You can't fight genetics, right ? Well, if you've bought that argument, then the actual science behind this concept will surprise and hopefully inspire you. Our genes are a factor, but so is our lifestyle, and lifestyle can be changed through conscious choice if the motivation is there.
The "fixed genetic set point" position is adopted by certain political groups in their platform to fight prejudice against fat people. The idea is that most obese people who try to lose weight end up failing repeatedly, so it is unfair to insist that they be unhappy with their current state. It's obviously a noble goal to fight against prejudice, and it's true that most people fight unsuccessfully against even moderate obesity. We have cultural ideals for thinness, especially for women, that are both unrealistic and unhealthy. I have no desire to feed those unrealistic and unhealthy ideals.
On the other hand, the truth is that a certain subset of people do successfully lose excessive body fat for the long run and in the process become measurably fitter and healthier, and visibly happier. There has never been any special biological or psychological factor found in common with all of these people who make successful changes. Neither have we ever found any particular factor that prevents other people from changing if they wish to. The difference lies in the choices we make. The science behind the "body fat set-point" will show us how to make intelligent choices.
First, let's look at the reality of the set-point concept. It has both strengths and weaknesses when we apply it to something as complex as body weight maintenance. But it does provide a nice, simple conceptual model for most of us. The easiest way to think of a set-point is to consider a thermostat or the cruise-control on a car. It is a mechanism that maintains some value in a narrow range by observing its own changes and modifying itself. The thermostat measures temperature and turns the heater or air-conditioner on if the current temperature varies from the desired one. The cruise-control gives more gasoline if the speed drops below the desired range and less if the speed goes too high.
The set-point concept is based on something known as feedback regulation, that is, regulating something based on getting information back from it. Human beings didn't invent feedback regulation, we learned it from nature. Feedback regulation is found nearly everywhere we find natural systems, from relatively simple chemical reactions to very complex living systems. Feedback regulation was first studied formally in the science of cybernetics. Cybernetics was originally intended to help develop missile guidance systems, but soon was found to have applications to many areas of life. Much of the modern discipline of cognitive science, and various modern schools of applied psychology are strongly rooted in cybernetic principles. The notion of a "set-point" was the engineering application of cybernetic feedback regulation.
The overall body weight of all animals remains within a remarkably narrow range, in spite of widely varying external conditions. This is true of humans, although humans are unique in that their weight varies so much from person to person. In most animal species, the body weight from individual to individual is much more consistent. The exact reasons for this unusual variance in human beings are not known. Even with this variance between people, an individual’s weight tends to be extremely stable over time under most conditions.
The stability of an individual’s body weight matches or surpasses the stability of most other physiological variables. Over a short period (6 to 10 weeks), body weight is found to vary extremely little. Average coefficients of variations are only .5 to .6 per cent of the mean.1 Even over longer periods, weight remains extremely stable. The average weight of a 60 year old white American male is only 4 to 5 pounds more than one 30 years of age.2
Lean muscle mass, bone density, and body fat all appear to be maintained in a narrow range. This is accomplished by a constant balance of anabolism and catabolism (building up and breaking down).3,4 In a similar fashion to the thermostat, organisms achieve internal stability. They do this by constantly monitoring their internal state and making delicate adjustments to maintain physiological variables at or near regulated values.
Note that the practical value of this concept does not rely upon our actually finding a physiological set point regulator. However, we have some good clues to how it works. The mechanism for the "body fat thermostat" appears to revolve around a brain structure known as the hypothalamus. The hypothalamus has a central role in many hormonal and regulatory functions in the body.5 The body fat regulation process also seems to use a recently discovered hormone called leptin. Leptin helps the brain determine how much fat is being stored6.
The brain also makes a chemical called neuropeptide Y. This chemical is linked to significant increase in appetite and an increase in insulin production, the unopposed effect of which would be gross obesity. The hormone leptin opposes the effect of neuropeptide Y, and this balance may be an important part of the body fat regulating mechanism. But many of the details are still a mystery.
Though the exact mechanisms of body weight regulation are unknown, the evidence that we vigorously and effectively defend a particular body weight is very strong. Rapid forced body weight gains and losses of up to 25% have been shown to be quickly reversed when the forced starvation or forced feeding is ended.7,8
The set-point concept applies to the obese, but to varying degrees. Of the few obese who successfully lose significant weight, most are likely to regain it over time, according to all research to date. However, it is usually possible to alter the "body fat set point" if you understand how it works ! Some people have done it, and the only thing common to all of them is that they incorporated healthy activity (and usually also healthy nutritional changes) permanently into their lifestyle.
An important popular fallacy to set aside is that an "obesity gene" predetermines that someone will be fat. The truth is that no gene has that degree of power over our body fat regulation. Our genes are indeed a factor in our metabolic rate, which is an important part of the regulation process. But they are only an influence, along with nutrition, stress levels, and activity levels. For example, the influence of genetics on body fat changes with activity. In the animal model of obesity (which is where the ob or "obesity gene" concept comes from), the predisposition toward obesity is easily countered by a little bit of extra activity. Exercise training reduces not only fat mass but also messenger RNA levels in the ob gene. This supports the hypothesis of a feedback loop between the fat cell and the hypothalamus in the brain. Consequently, we can maintain body weight at a constant level by reducing ob gene expression in response to increased energy expenditure.9 If it's fair to apply the animal obesity model to point out that people can be "genetically obese," then it's also fair to point out that those same animals have been demonstrated to avoid obesity if they exercise.
We are perfectly capable of compensating for most genetic differences in metabolism by increasing our activity by a reasonable amount.
If we go back to the analogy of the thermostat, we are saying that the "body fat thermostat" has a dial, and that dial is our activity level. Just because our body aggressively maintains a stable amount of body fat at a target level doesn't mean the target level can't be changed. Just as we can turn the dial on a thermostat to change the temperature maintained, we can fine-tune our lifestyle to change the amount of body fat and out overall fitness level.
The way that our body maintains such a narrow range of weight over a wide variety of dietary and environmental conditions is by both altering our food intake (through changes in our appetite) and by changing our metabolism, especially the rate of burning fat through a process called thermogenesis. Important measures of metabolism are our basal and resting metabolic rates. These are standardized rates at which we burn calories when we are not active.
The most important biological factors so far discovered for maintaining our fat weight seem to be :
Each of these plays a slightly different role in the process, and contributes to its complex characteristics.
The set point is established by a number of different interacting factors, including : genetic factors, physical activity levels (activity demand), level of sex hormones, level of stress hormones, nutritional status, various anabolic or catabolic drugs, various "psychological" factors (such as body image), and neural damage. These all contribute to maintaining the levels of both lean muscle mass and body fat.10
Exercise physiology professor Claude Bouchard of Laval University in Quebec estimates that 35 to 40% of the variance in weight among people of the same height can be attributed to genetic factors. This leaves 60-65% of the factors within our direct control if we can control our environment and our habits intelligently. And if the animal model of genetic obesity (the ob gene) applies to humans, we may even have some control of the genetic set point by altering our activity level.
When we purposely reduce our caloric intake and begin to lose weight, our metabolism slows considerably (becomes more energy efficient) in order to maintain our body weight at the reduced input. Similarly, when we take in excessive calories and begin to gain weight, our metabolism quickens (squanders more energy) to compensate.
There are probably at least two different mechanisms at work here. One kicks in right away when we restrict calories and serves to maintain both lean body mass and body fat. The other kicks in more slowly and only works to maintain body fat stores. The maintenance of body fat appears to be much more aggressive in lean people than in obese people. The fall in metabolic rate is much greater in lean people. This is good news for the obese, but means that it becomes increasingly difficult to lose those last few percent of body fat once we are lean because out body hangs on to them much more stringently. 11
Part of the slowing of metabolism when we diet is due to a loss of metabolically active body tissue, but the change in metabolism is greater (approximately 15% greater) than can be accounted for by that mechanism. The incompletely understood mechanism by which this metabolic change occurs appears to have to do with changes involving the muscle tissue. When eating excessively and gaining weight, both basal metabolism and the energy cost of exercise increase to help burn off extra calories and slow down weight gain. The reverse happens when we restrict calories, to help slow down weight loss.
A result of this process is that after starving ourselves, we gain weight very rapidly when we resume normal eating patterns. Similarly, after temporary overeating, we lose weight very rapidly when we resume normal eating. Another result of this process is that it is generally impossible to maintain a reduced weight while eating normally. Following weight loss, our energy expenditure is reduced, allowing us to gain weight on less food.
When calories are restricted, metabolism slows within 24 to 48 hours and continues dropping by about 15-30%, regardless of the body weight of the individual. For example, decreasing from 2000 to 1500 calories causes body fat to burn at about 40 grams per day, but this rate slows to 20 grams per day by the end of the second month. By the end of the third month, the rate of fat burning slows to 10 grams per day, and then stops completely soon after.
This illustrates how the slowing of metabolism causes the body to limit weight loss under reasonable changes in diet. This is probably the main cause of the infamous "dieter's plateau" that causes many people to give up on weight loss programs. This is particularly unfortunate because the decrease in metabolism is temporary. The body adjusts to its new body fat set-point if it remains there for an extended period, especially if our activity level remains healthy rather than going back to being sedentary. This is one of several reasons why a gradual fat loss program focused on activity and fitness is often more effective than a rapid "diet"-based fat loss program.
From both human studies and animal models, we see that fatter individuals generally eat more than lean ones. But when we consider the difference in metabolically active tissue we find that they are eating just enough to maintain their additional tissue. That is, they have a higher set point, and their eating habits reflect the maintenance of their body tissue, like anyone else. Except that maintaining their excessive fat tissue is not healthy or efficient. Their primary problem is not necessarily that they are guilty of bad eating habits. In fact, many obese people eat surprisingly little food to maintain their body fat level. This set point model is particularly appropriate to people near normal body weights, and also applies to many, but probably not all, obese people.
There are currently five primary ways known for changing the body weight set point :
Stress is an important factor not to be ignored. One Yale University study of 41 overweight women ages 18 to 40 found a significant correlation between those with excess abdominal fat and those who had an elevated cortisol (stress hormone) response to stressors perceived to be outside their control. It is notable that dieting itself can often provide such a stressor, resulting in a dangerous loop that more aggressively deposits body fat to the most visible area as we more aggressively try to diet it off. Stressors outside our control, particularly when they invoke a combination of adrenaline and cortisol, cause fat to be redistributed from legs and other areas to our middle. The elusive culturally inspired goal of the flat stomach can become a biological trap for some people, particularly women who try to achieve it through dietary restriction. Meditation and light exercise of various kinds are both extremely effective for stress reduction.
Behavioral conditioning is a useful adjunct to any fat control program. There are a number of different effective techniques, ranging from cognitive strategies (changing the way we think about food), to hypnosis therapy.
Appetite suppressants are a tricky issue. Most of them that work have serious side-effects, and the most effective for the longest period have the worst side-effects. Even if that weren't the case, the idea of relying on a drug or supplement to lose weight serves as a negative message to yourself, as if you were admitting that you can't control your nutritional practices and activity level enough to become more fit. One of the main differences between the various drugs and supplements is that they stop working at different points. The most successful are those that continue to maintain a new body fat level for a year or two without requiring us to increase the dosage or change what we are taking. But even with the most successful appetite suppressants currently used, the results often end when the drug is discontinued. The rest of the lifestyle factors keeping the "dial" where is was are still in place, so we gradually go back to our old body. Consider this approach only as a last resort, in a category with surgery and other extreme measures. A fitness-based approach has a great many advantages. Most "fat-burning" supplements have no lasting influence on metabolism, and even the most promising so far have a relatively insignificant effect compared to proper nutrition and activity. The role of supplements should be to support good dietary and exercise habits rather than to replace them.
There are several prime candidates left: (1) changes in diet, (2) resistance training, and (3) endurance training.
As we've seen, severe calorie restriction does alter the rate of fat burning. It decreases it ! Very low calorie diets have the effect of causing us to lose muscle mass, which in turn lowers our basal metabolism and slows down our ability to burn fat under all conditions. Even heavy weight training and anabolic steroids do not have much effect on preserving lean mass if we maintain a very low calorie diet. This is a tactic of last resort only for those who cannot become active for some reason but still need desperately to lose body weight.
More moderate changes in diet can have more positive effects, in combination with appropriate activity and stress control.
Moderate healthy dietary changes involve a balance of different nutrient-rich foods, emphasizing lean proteins, fiber, fruits, vegetables, and grains, and to a lesser degree, monounsaturated fats. There is a theory among some popular authors that dense carbohydrates should be avoided because of their effect on insulin levels, but this is not a generally accepted practice. It does produce fat loss in many people, especially in the short term. However, it often tends to result in nutritional programs that are too low in overall calories, too low in fiber, and missing some potentially important nutrients. Thus it may not be a healthy strategy for the long term, which is what we are striving for.
This leaves us with the question of whether endurance training, strength training, or both, is most effective for lowering the body fat set-point. One telltale study suggested that (in people who are not restricting their food intake !) 12:
The upshot is that combining resistance and endurance training is the most effective strategy for losing body fat quickly. However, this strategy produces diminished results from both the strength and endurance facets of training.
This is a very powerful argument for an individualized training program designed to suit your particular needs, whether they are fat loss, more muscle, more strength, or more aerobic endurance.
It is useful to ask how "dieting" might alter the results, since most people change their intake as well as their activity level when they begin a program. We already know that restricting calories by too much sabotages our efforts, at least in the short term, by causing our metabolism to slow down. We also know that metabolism is largely proportional to the amount of muscle we have, and that we need to get adequate protein and total calories in order to maintain or increase our muscle. So we certainly don't want to starve ourselves, or go on extended fasts, if we are trying to make long term losses of body fat. But we also know that much of the excess energy taken in, in the form of food, is deposited as body fat. So there is an optimal range of energy intake, based on the amount and kind of activity you are doing. There are also very strong influences on metabolism based on what kind of things we eat, especially in combination with exercise. 13 There are some generally good practices, and some practices that vary for different people depending on their individual medical profile and their goals. This is where reading quality books and publications and having a competent trainer or nutritionist available can be invaluable. This is also an area where following fads or unthinkingly adopting what works for someone else may set you back.
This process is most difficult in the beginning, but becomes easier over time. It becomes easier both because our body adapts to the new setting and because making the right choices goes from being a conscious decision making process to becoming a habit. The specific changes we get depend upon the specific combination of lifestyle changes we make. Most changes involve a compromise, and this is where it helps to learn all the quality information you can about nutrition, exercise, and stress, and their effects on the body.
Notes:
2
Ten-State Nutrition Survey 1968-1970. U.S. DHEW Publication No. (HSM) 72-8131.3
For a technical introduction to the concept of body fat set point in research, see Keesey, Richard E. (1980). "A Set-Point Analysis of the Regulation of Body Weight," in Stunkard, Albert J., Obesity. W.B. Saunders Co.. Other technical sources include Harrison, D.E., et al., (1984). Proceedings of the National Academy of Sciences, USA 81 : 1835; Bennett, W. (1984). "Dieting Ideology vs. Physiology," Psychology of Clinical Nutrition, 7: 321-334; and Mrosovsky, N. and Powley, T.L., (1977). "Set Points for Body Weight and Fat." Behav. Biol., 20:205-223. A good popular book on the subject is Remington, D., Fisher G., and Parent, E., (1983). How to Lower Your Fat Thermostat, Vitality House, Provo Utah.4
Technical criticisms of the use of the set point concept may be found in "Engelberg, J. : Physiological regulation : The steady state. The Physiologist, 9:69-88,1966" and also in "Wirtshafter, D. And Davis, J.D. : Set-points, setting points, and the control of body weight. Physiol. Behav., 19:75-78, 1977."5
Grossman, S.P., (1975). "Role of hypothalamus in the regulation of food and water intake." Psychol. Rev. 82, 200-224.6
Travis, J., (1996). "Obesity researchers feast on two scoops." Science News, Vol. 149. January 6,1996.7
Sims, E.A.H., and Horton, E.S. : Endocrine and Metabolic adaptation to obesity and starvation. Amer. J. Clin. Nutr., 21:1455-1470, 1968.8
Keys, A., Brozek, J., Henschel, A. Et. al. (1950). The Biology of Human Starvation. University of Minnesota Press, Minneapolis.9
Friedman JE, Ferrara CM, Aulak KS, Hatzoglou M, McCune SA, Park S, Sherman WM, (1997). "Exercise training down-regulates ob gene expression in the genetically obese SHHF/Mcc-fa(cp) rat." Horm Metab Res May;29(5):214-21910
A good overview is found in Bennett, William and Gurin, Joel, (1982). The Dieter’s Dilemma : Why Diets are Obsolete - The New Setpoint Theory of Weight Control. Basic Books.11
Dulloo, Abdul G. & Jacquet, Jean, (1998). "Adaptive reduction in basal metabolic rate in response to food deprivation in humans: a role for feedback signals from fat stores." Journal of Applied Physiology, 85:2, 599-606.12
Dolezal, Brett A., & Potteiger, Jeffrey A., (1998). "Concurrent resistance and endurance training influence basal metabolic rate in nondieting individuals." Journal of Applied Physiology, 85:2, 695-700.13
Whitley, Helena A., Humphreys, S.M., Campbell, I.T., Keegan, M.A., Jayanetti, T.D., Sperry, D.A., MacLaren, D.P., Reilly, T., & Frayn, K.N. (1998). "Metabolic and performance responses during endurance exercises after high-fat and high-carbohydrate meals." Journal of Applied Physiology, 85:2, 418-424.