Dear DOCTOR Owen:

Whenever I over-eat, I become very hot and sweat. In addition, my heart races. Sometimes it feels as if I have a hard time breathing, and my respirations increase. I worry that there is something wrong. My doctor assures me that all the tests are normal. I am not overweight. I should be heavier, considering how much I apparently over-eat. Do other people have problems similar to mine?

Hot and Bothered

Dear “Hot”:

You are experiencing something called thermogenesis, which means that you create and disperse heat after over-eating. Everyone experiences this to some degree. However, some individuals may have a greater propensity to do so. I wonder: “Are you also somewhat nervous and fidgety?”

Even as early as the 1800s, scientists noted and attempted to measure thermogenesis after eating. This was proposed, but never proven, to be the reason why some people appear to eat like pigs and never get fat. In fact, it is known that a percentage of energy from food is used to break down and store excess food. The amount of energy required to do this varies with the type of diet and from person to person.

A comprehensive review of over 1,000 articles on this subject was published in the International Journal of Obesity, Vol. 23, No. 11, 1005–1118, which reviewed studies from the 1800s to the present, as well as animal and human experiments. In summary, some people disperse more heat and energy than others after eating large meals. As little as 20% and as much as 40% of the excess calories were “burnt” off by raising body temperature, heart rate, breathing, and muscle activity. The rest was stored as fat. Diets very low in protein were found to cause the greatest “waste” of calories.

Some studies find that diets very high in protein and low in carbohydrates also cause excess heat dispersion.

When describing why people genetically become overweight, it is usually suggested that a normal “wild” diet is very low in fat and high in vegetable matter. It has been suggested that our current high-fat diet causes obesity because of our genetic background of low-fat diets throughout the millennia.

Some of the researchers reporting in these articles propose an additional theory: Very fat, overweight humans and animals are not as able to hunt, fight, and mate as effectively as lean, muscular individuals. Therefore, genetically, people may be able to disperse excess calories from a gluttonous meal without very much weight gain. This would keep individuals who continue to hunt and gather food for survival within a small fatness range.

This is certainly an interesting and alternative way of thinking. It could explain why some people lose weight very well on restrictive diets, such as a very high protein diet, and others lose very little. At either extreme—very high protein or very low protein—adverse health consequences could theoretically occur. Low-protein diets are associated with decreased immunity, decreased growth, and healing. High-fat diets are associated with accelerated atherosclerosis, heart attacks, and strokes (which kill 70% of all people in the developed countries).

I have had similar responses to over-eating more times than I care to admit. I am sure that my friends wonder whether I really “pay back” those calories or if I am “naturally” thin. Since I exercise about an hour a day and drink liquid food five days a week, I “feel” that it is the payback. Perhaps it’s a little of both.

I call your reaction (and mine, when it occurs) a form of “food poisoning.” For example, I physically feel bad until the food is long gone, and it takes considerable very low calorie payback for me to feel healthy again. I am certain that this gluttonous over-eating is taking a toll on my longevity. It’s always amazing to me how much we can abuse our bodies and live as long as we do!

This column probably adds to the confusion of people who are looking for simple answers to questions about obesity. I hope it does because obesity is one of the most complex and challenging disorders facing medical science today. While everyone can lose weight, there are great person-to-person differences in why it is difficult to maintain that loss. Simple it really is not.