The set-point theory describes the regulation of body weight. According to this theory, each person has a specific body weight at which he or she is relatively well, and which is kept constant by the metabolism under normal conditions. The level of this individual weight is called the set point. Its exact value is probably innate and cannot be significantly affected permanently or long-term without causing health difficulties. This means that the body strives to maintain the initial weight that is normal for it – the set point.
Weight levels off
It is possible to lose weight below the individual set-point weight in the short term, but in the longer term the weight will swing back toward the starting point. Counter-regulation occurs, which counteracts excessive weight loss. The same principle also applies in the opposite direction: following a high-calorie “fattening diet“, special changes occur in the metabolism, so that over a longer period of time the former, normal starting weight (set point) is reached again. The findings about the set point are not new. As early as the 1950s and 1960s, scientific studies were conducted on the effects of weight reduction or high-calorie diets on body weight and well-being. Some of this research is still considered classic today.
Set-point theory studies
Probably the most important study was conducted in 1950 in the USA by Keys’ research group. The aim of the study was to investigate the consequences of starvation on mental and physical well-being. Young, mentally healthy men of average weight participated in the study. The total duration of the study was one year. During the first three months, the men ate normally, according to their previous eating habits. In the following six months, the actual diet phase, the individual amount of calories was halved. Under this reduction in calories, the participants lost an average of 25 percent of their body weight. In the last three months of the study, the participants were again given increasingly more to eat and accordingly slowly regained weight.
Even healthy people change behavior
In addition to the weight change, the results showed surprising deviations in the men’s behavior: during the diet phase, their thoughts were increasingly preoccupied with food and they were able to concentrate less and less on other things. This applied not only to topics of conversation, but also to reading material. Some started reading cookbooks and collecting recipes. They spent a lot of time thinking about upcoming meals. In some cases, participants spent hours eating a meal that would have taken them only a few minutes in the past. They also experienced large mood swings. Most became irritable and nervous, and many depressed. They lost interest in social contact and became increasingly withdrawn. The ability to concentrate and comprehend decreased significantly.
Sense of hunger lost
The same thing happened with physical performance. Many experienced sleep disturbances or gastrointestinal complaints. The basal metabolic rate, and thus the energy consumption of the participants, was reduced by approximately 40 percent. As a result, the men lost less weight than would actually have been expected due to the reduction in calories. During the diet phase, the men experienced binge eating for the first time, which they were ashamed of. The normal sense of hunger, satiety and appetite was completely lost in most of them. These problems continued for a while after the diet ended. In the final phase of the study, participants regained weight and returned to their baseline weight.
What causes weight gain?
Another important investigation looked at the extent to which a person’s weight increases as a result of a large increase in the number of calories consumed each day, and what the consequences are for mental well-being. This investigation was carried out in 1968 by the American research group around Sims. 15 men increased their weight by 25 percent within six months. Initially, most of the participants gained a few kilograms without any problems. However, this changed in the further course: Only four men gained significantly due to overeating (maximum 10000 Kcal. per day).The remaining participants had to make enormous efforts for further weight gain and eat large meals with a lot of effort in order to gain enough weight as well. Under the condition of high-calorie diet, the basal metabolic rate of the participants had increased greatly.
Baseline weight after overeating
That is, the metabolism consumed more calories by producing more heat and sweat, for example. For this reason, the observed weight gain was limited and less than would have been expected based on caloric intake. Three participants had not reached the 25 percent weight gain goal by the end of the study. After the overeating stopped, the majority of participants quickly lost weight and returned to their baseline weight. Only two men remained overweight; these two had a family history of obesity and gained weight rapidly and easily from the beginning of the study.
Conclusion: set-point theory
The results support the set-point theory, according to which individual body weight is to a large extent biologically determined. Diets are not a permanently effective method of weight regulation because specific metabolic mechanisms counteract the diet, thus “defending” the set point. That is, the weight is stabilized at the level of the initial weight. Irregular eating, fasting, vomiting, binge eating, and the use of laxatives or appetite suppressants have as a common effect a significant disruption of the normally present feelings of hunger and satiety. Therefore, all the characteristics of anorexia or binge eating can occur even in previously healthy people (with normal eating patterns) in the context of a severely calorie-restricted diet.
