Copyright © 2007-2018 Russ Dewey
One idea from Hull's theory remains very current. That is the idea that biological motives resemble control systems or regulatory systems.
Research has shown that biological motives like hunger and thirst do indeed operate as homeostatic systems, regulating basic biological variables. Weight control, for example, is related to energy regulation in the body.
Which idea from Hull's theory remains current?
Richard Keesey and colleagues coined the term set-point to refer to a level of fat in the body kept at a certain level (Keesey 1978). Fat cells are elastic.
If animals are given access to adequate supplies of food and left alone, the fat cells stay constant in size. This indicates some sort of regulatory process.
Why is fat regulated so closely? Fat is the most energy-dense substance in the body. By regulating levels of fat, the body regulates storage of reserve energy.
The natural or ideal level of fat in your body is what Keesey called the set-point. The concept of a set-point is particularly reminiscent of Hull's assumption that motivation is homeostatic: aimed at maintaining a crucial variable within an ideal range.
Despite the word "set," the set-point is not necessarily any more fixed than the setting on a thermostat. A better label for the set-point might be the defended body weight. It can be changed, but not easily in most humans.
The set-point is apparently altered by bariatric surgery (removing portions of the digestive tract) in both humans and animals. This led Hao and colleagues (2016) to refer to "reprogramming the defended body weight" as a distinct possibility.
Obesity researchers are intensely interested in the altered set-point phenomenon and whether it might be done without surgery. If so, it could revolutionize approaches to weight loss in humans.
What does it mean to say the body "defends" the set-point? What is evidence the set-point can change?
A dieter does not lose fat cells; rather, each fat cell shrinks. When the fat cells get small enough, the organism takes action to restore fat levels to a higher level. That is what it means to say the organism defends a particular body weight.
The following compensations occur when fat levels fall below the set-point, as part of the organism's active defense of a body weight or set-point:
1. The basal metabolic rate or BMR, the background level of energy consumption in the body, is reduced. Body heat is lowered.
2. More calories are extracted from food as it is digested; fewer calories are excreted in waste products.
3. Activity level, except for that directed at food, decreases to conserve energy.
These changes make it harder to lose weight when fat falls below normal levels. It also makes fat easier to store after a diet. That is why, as a rule, people regain the weight they have lost during a successful diet.
The prospects for long-term weight loss are not quite as bad as some headlines proclaim. The widely reported claim that 98% of dieters will gain back everything they lost is based on a 1959 study of 100 obese individuals by Stunkard and McLaren-Hume (1959).
What were factors associated with long-term weight loss?
More recent studies indicate about 20% or 1 in 5 obese individuals can maintain weight loss. That is defined by loss of 10% or more of body weight for more than one year (Wing and Phelan, 2005).
Some people generate low numbers of fat cells. They are naturally thin, with a low set-point.
Such people find it difficult to gain weight no matter how much they eat. The more calories they consume, the more efficiently their bodies burn off the excess calories. Thus they "defend" their low weight.
This energy burn-off takes the form of metabolic adjustments that are the opposite of those listed for people with high set-points. After a big meal, the naturally thin person will experience the following compensations:
1. Basal metabolic rate and body heat rise as the body's cellular engines are turned up a notch and extra calories are burned off.
2. Less energy will be absorbed from food, as the body cuts back on insulin, which converts food to energy.
3. Activity levels and fidgeting increase after a brief rest.
What happens when a person who is "naturally skinny" eats a rich meal?
Most people do not consider natural thinness to be a problem. Fatness is more of a worry.
A person with a high set-point can lose weight but will usually put it right back on after resuming previous eating patterns. To make matters worse, each rebound from dieting tends to raise the set-point a little bit.
So is dieting hopeless? Not entirely. The existence of a storage system for fat does not mean fat levels are permanently fixed and cannot change. The opposite is true. To be useful, the fat must be accessible.
Fat is like money in a bank account. It is only helpful if you can get it out when you need it; otherwise there is no point in storing it.
How does one withdraw fat from the fat bank? Create conditions in which the body must draw upon its energy supplies. Take in fewer calories, increase energy consumption by exercising, or do both.
How can weight be lost, despite the influence of the set-point?
Wing and Phelan (2005) summarized factors most likely to produce lasting weight loss instead of a return to previous levels:
1) engaging in high levels of physical activity;
2) eating a diet that is low in calories and fat;
3) eating breakfast;
4) self-monitoring weight on a regular basis;
5) maintaining a consistent eating pattern; and
6) catching "slips" before they turn into larger regains.
The researchers also noted that "initiating weight loss after a medical event" or on the advice of a doctor was associated with longer-lasting weight loss.
Successful dieters engaged in self-monitoring. They kept records systematically. That is often part of successful behavior change programs, whether they are aimed at personal finances, weight loss, or anything else.
Some weight-loss programs refuse to use the word "diet" at all, because it implies a temporary change. They work with a philosophy more like alcoholism treatment programs. To produce a lasting change, one must adopt a new way of living.
Another way to produce lasting change is to surgically alter the body. Backsliding (regaining lost weight) occurs with almost all dieting programs, but it does not seem to occur with bariatric surgery, where portions of the stomach are actually removed.
Those patients report a change in tastes and appetites. For example, sweetness becomes less attractive (Pepino et al., 2013).
A permanent change like that suggests alterations of body chemistry resulting from the surgery. Perhaps that could be imitated by pharmaceutical interventions. That gives hope for more effective non-surgical dieting aids in the future.
Consequences of Severe Dieting
Some people succeed in taking off enormous amounts of weight without surgery, going from grossly obese to a normal weight. Although they may look more normal to the outside world, such people are often quite abnormal in their body physiology.
Rockefeller University researchers followed a group of successful dieters from Overeaters Anonymous who lost more than 200 pounds. After a severe diet, these individuals had a normal weight according to "ideal weight" tables.
However, such people were biologically abnormal. Their fat cells were tiny and their hormonal output was like that of a starving person. (Hirsch, 1988)
What did researchers discover about people who lost more than 200 pounds?
A person with anorexia nervosa–the starvation disease–has tiny fat cells. Such a person is likely to experience disturbances such as irregular heartbeat, insomnia, intolerance of cold, and mood fluctuation
Anorectics (people with anorexia nervosa) have low white blood-cell counts and abnormally low heart rate and blood pressure. They are intolerant of cold. They tend to be obsessed with food. Anorectic women do not menstruate.
The Rockefeller University researchers found characteristics of anorectic people in those who were formerly obese and now at so-called normal weight. To maintain their weight loss, they had to eat 25% less than people without a history of obesity.
To keep their fat cells almost empty of fat, they had to tolerate being cold much of the time. Virtually all the women stopped menstruating. They tended to be obsessed with food. (Kolata, 1988)
In summary, it is possible to go from extremely obese to normal in weight, but the price is great. One remains in a perpetual state of starvation, physiologically.
Factors Influencing Fat Deposition
What factors influence a person's ultimate weight? Twin studies indicate that genes account for about 80% of the expected variation in a person's adult weight.
However, this does not mean that calories do not count. The genetic influence is probably expressed in satiety variation (how easily a person feels full and stops eating).
The genetic influence explains why identical twins usually weigh about the same and put on weight at the same periods in their lives, even if they have been reared apart since birth. Children who are adopted end up with a body mass that correlates with their biological parents, not their adoptive parents (Bray & York, 1979).
What is evidence for genetic influences on fatness?
Over half of obese humans admit to binges of eating. Binge eating stimulates formation of more fat cells.
The two main causes of obesity–genetics and overeating–can be distinguished in laboratory animals by testing for abnormal secretions of adipsin, a chemical produced by fat cells. Genetic disorders that produce obesity are marked by abnormalities in adipsin release.
What does research suggest about the effect of exercise on weight loss?
Does exercise help dieters? For the average college student, the answer is probably yes.
However, exercise is difficult for people who are extremely obese. Those people have a low capacity for strenuous exercise. As one expert noted, "If you are obese enough to need to exercise in order to lose weight, you probably won't be able to exercise enough to boost your body's metabolism" (Kolata, 1987).
Even in non-obese people, evidence for an effect of exercise on weight loss is surprisingly thin. While exercise does burn calories, successful dieters do not seem to require exercise as a condition for losing weight. Dieters succeed just as often without it.
What does research show about fidgeting?
Exercise of the workout variety may not be as important as constant, smaller scale activity. Studies indicate that fidgets–small movements people make without thinking about it–consume more energy than planned exercise programs.
Technically, fidgeting is called "nonexercise activity thermogenesis" (NEAT). Research indicates that when most people overeat, "activation of NEAT dissipates excess energy" (Levine, Eberhardt, & Jensen, 1999).
That explains why some people eat high-calorie meals without gaining weight. People who become obese often have a lower NEAT level, making it harder for them to burn off excess calories.
What does Hirsch recommend to people who are "born fat"?
Jules Hirsch of Rockefeller University is a proponent of the theory that "People are born fat." He recommended a moderate amount of dieting and a moderate amount of exercise.
"My chief advice is that people be aware of what they are eating and making changes, however small, that they can stay with forever" (Kolata, 1988). He also recommended that obese people increase their daily exercise in regular, unobtrusive ways, such as taking stairs instead of elevators or "parking their car farther from their homes or offices and walking the extra distance."
Satiety (suh-TIE-ity) is the condition of being full. Theories about defending weight levels or fat levels cannot explain why we stop eating at a particular meal, because we stop eating well before the fat enters our cells. Research suggests satiety signals arise from the stomach.
Deutsch, Young, and Kalogeris (1978) implanted a tube below the stomach in rats. They siphoned off milk as the rats drank it, so the milk never reached the large intestine.
Instead of drinking more than usual, the rats drank the same amount as usual. The arrival of milk in the stomach was apparently enough by itself to generate the "satiety signal" that shut off hunger.
What is satiety? What causes satiety?
This kind of research, showing that a full stomach led to a feeling of fullness or satiety, led to development of a weight-loss device called the gastric bubble. The gastric bubble was a small plastic balloon inflated in a patient's stomach. The balloon occupied space in the stomach, leading to feeling of "fullness" after relatively little eating.
A gastric bubble
The gastric bubble proved to cause complications in some patients, and it deteriorated after a time. Researchers started turning their attention toward a more permanent approach: reducing the size of the stomach.
Doctors tried stapling the stomach, fitting it with a constricting band, stimulating it with mild electric current, or surgically removing part of the stomach or large intestine. All of these approaches have been tried with obese people, all with some success, but also with some complications and failures.
The least radical approach is the gastric band, because it can be removed. It shrinks the effective size of the stomach, reducing the amount of food it takes to feel full.
The peak of popularity for the gastric band was 2011, when it was approved as a medical device. By 2016 it had fallen out of favor. "The most common operation with the band now is an operation to remove it," said one bariatric surgeon interviewed by Kolata (2016).
More popular than the gastric band now is the gastric sleeve operation, in which most of the stomach is removed. Stapling is used to create a smaller "sleeve" through which food passes. That accounts for nearly half of bariatric surgery in 2016. Gastric bypass surgery, which also involves shrinking the stomach and attaching it to the small intestine, is also popular.
Gina Kolata, who reported on obesity and dieting related issues for over 30 years for the New York Times, followed two patients who received bariatric surgery. The size of their stomachs was reduced to about the size of an egg. It worked; both the male and female patients lost weight and kept it off.
Their food preferences changed, as often noted after bariatric surgery. One patient reported that her incessant urges to eat vanished. "Another, who used to seek fatty and sugary foods, said, 'I crave salads now.'"
The female lost 90 pounds, the male lost 93, during the year Kolata followed them. However, both said that their lives had not changed as much as they expected.
There were definite benefits: their joints ached less, they reported more energy, and they no longer had to use prescriptions for diabetes and high blood pressure. But both people still felt fat, even after the weight loss.
Both found that life had not changed much. They still faced challenges when it came to succeeding in school, on the job, or finding romantic partners. Weight loss was welcome, but it was not an all-
Bray, G. A. & York, D. A. (1979) Hypothalamic and genetic obesity in experimental animals: an autonomic and endocrine hypothesis. Physiological Review, 59, 719-809.
Deutsch, J. A., Young, W. G., & Kalogeris, T. J. (1978). The stomach signals satiety. Science, 201, 165-167.
Hao, Z., Mumphrey, M. B., Townsend, R. L., Morrison, C. D., Munzberg, H., Ye, J., & Berthoud, H. (2016) Reprogramming of defended body weight after Roux-En-Y gastric bypass surgery in diet-induced obese mice. Obesity, 24, 654-660. doi:10.1002/oby.21400
Hirsch, J. & Leibel, R. L. (1988) New Light on Obesity. New England Journal of Medicine, 318, 509-510. doi:10.1056/NEJM198802253180808
Kolata, G. (1987). Metabolic Catch-22 of Exercise Regimes. Science, 236, 146-147.
Kolata, G. (1988, February 25) New York Times Retrieved from: https://www.nytimes.com/
Kolata, G. (1988, February 25) New York Times Retrieved from: https://www.nytimes.com/
Kolata, G. (2016, December 27) After weight-loss surgery, a year of joys and disappointments. Retrieved from: https://www.nytimes.com/
Levine, J. A., Eberhardt, N. L., & Jensen, M. D. (1999) Role of nonexercise activity thermogenesis in resistance to fat gain in humans. Science, 283, 212-214.
Pepino, M. Y., Bradley, D., Eagon, J. C., Sullivan, S., Abumrad, N. A., & Klein, S. (2013) Obesity. Retrieved from: https://www.ncbi.nlm.nih.gov/
Stunkard, A. J. & McLaren-Hume, M. (1959) The results of treatment for obesity. Archives of Internal Medicine, 103, 79-85.
Wing, R. & Phelan, S. (2005) Long-term weight loss maintenance. American Journal of Clinical Nutrition. Retrieved from: https://ajcn.nutrition.org/
Write to Dr. Dewey at firstname.lastname@example.org.