Continued from last week: Last week I began a discussion about the theories of weight control from an article in the Harvard Mental Health Letter (October 1991). The first was called the "three-bears" theory and related to eating too much because we like food or are lonely, etc. The second (the pica theory) said that we eat too much because we need a certain nutrient we are not getting. The third was the fat-thermostat (fat-stat) theory. This theory suggests that the body is programmed to accumulate a certain amount of fat and that we eat to maintain that amount of fat.
Which theory is correct? Based on recent research, Dr. Bennett (the author of the article) felt that the fat-stat theory was becoming the most plausible and the overeating hypotheses were less likely to be correct. I'll summarize some of the research he mentioned to support this view:1. Genetic: In the past 10 years, studies have consistently shown that fatness is somewhat heritable. In fact, from half to two-thirds of the difference in body fat between any two people may be attributable to their genes. Genetic effects intensify with age: Children come more and more to resemble their parents, twins to resemble each other.
When obesity is mild or moderate and develops in adult life, it appears to be the result of multiple genes acting in concert, especially with inactive people living in an environment with abundant food. In one study where 84,000 calories were consumed over a 14-week period, identical twins gained weight at about the same rate; unrelated people had a much wider variation, gaining anywhere from 9.5 to 29 pounds with the same increase in calories.
2. Metabolic: Research with twins and people who are at a high risk of obesity such as the Pima Indians suggests a "thrifty genotype" hypothesis. Apparently, some people are programmed to have a large amount of fat. When they are at levels below this programmed level, their body slows down metabolically until the "proper" level is reached; then their metabolic rate increases and becomes "normal."
3. Fat localization: The fat on the body is not all alike, and there are several important fat deposits: the subcutaneous fat of the chest and abdomen; the fat surrounding the viscera within the abdomen; the subcutaneous fat of the hips and thighs; and, in women, the breasts. The fat in these different locations is subject to different kinds of neuroendocrine control and has different metabolic implications. For example, intra-abdominal fat is most quickly deposited and most easily lost. It is also associated with the most significant endocrine changes, and people with high abdominal fat accumulations are at higher risk for heart disease. These findings support the view that fat storage is linked with other body systems and not simply a passive, unregulated consequence of disturbed eating behavior.
It is becoming clear that in the long run, both food intake and body fat are consequences of the equilibrium in a complex system that involves changes in fat stores, metabolic rate and endocrine regulation. It is doubtful that "dieting" in the traditional sense will ever be an effective treatment for long-term control of obesity.