The "fat cell" theory also applies here, and seems to correlate with the "set point" philosophy. It has been shown that we each develop a specific number of fat cells in our body. This mainly occurs at certain times of life—before birth, during infancy, and during the adolescent growth phase. This may be genetically determined, but it also appears that if we are overfed or overeat during these times, we may create more fat cells. At other times, as in our adult life, we increase only the size of our cells. When we take in more calories than we use, our cells and fat stores get bigger. So a trim person may have a lower number of cells, or the same number of smaller cells than a heavier person, but when we lose weight and become thinner, our fat cells become smaller.

This process involves primarily "white" fat found mainly in the fat cells that lie under our skin. This is our energy, or calorie storage fat. The "brown" fat, or the "good" fat, actually burns calories for body heat. This fat is deeper and surrounds and protects our organs. Normal fatty acid metabolism supports and nourishes the brown fat. The storage, or white, fat is where our body puts the extra calories from dietary sources that we do not utilize. When we diet regularly or our weight goes up and down, our internal weight control system fears starvation and will store more fat as energy for the future. With repeated weight loss and weight gain, the same number of calories in our diet may keep us at a higher weight because we have a higher set point.

When we have developed more fat cells during our growth periods (infancy and adolescence), we will tend to have more fat, a slower metabolism, and a higher set point, and we will be more likely to have a higher weight. Once this pattern develops, such as by being overweight early in life, it is very hard to change. It takes work and a new self-image! Regular exercise and increasing exercise capacity are the main physical ways to improve the set point and lose weight and then to be able to maintain our weight with a reasonable number of calories. This is a far healthier approach than taking thyroid pills or one of the many possible diet stimulants.

Other ideas about individual weight suggest two opposing views. One school says that people are thin because they do not overeat as much as fat people, since they are guided more by internal signals of hunger and the types of food that their bodies want. Overweight people on the other hand respond more to external signals, such as the presence of food or other people and social situations, or they may react more emotionally to the normal internal messages.

Others believe that obese people do not really eat a great deal more than thin people; they just have a different set point and a slower metabolic rate. Heredity and early conditioning play a major role here. Heavier people’s food choices may not be as wholesome as those of thin people, with higher-fat and higher-calorie foods predominating. Malnutrition from nutrient deficiencies and food allergies can also be influential. Obesity is really a combination of these many factors. Of course, most of us know overweight people who eat a lot of food. Then again, we may know overweight people who eat lightly, as well as trim people who can really put it away. Most overweight people, I believe, have overeaten at some point to develop their capacity for obesity, unless there is some hormonal imbalance, which is not very common.