For many years now it has been known that many animals, ranging from simple organisms like yeast all the way up to mammals, can extend their life span, even their normal life span, by restricting their caloric intake. Mice, for example, given less than their usual caloric intake, live longer, and healthier, than mice from the same litter that have eaten a more typical diet. Their lower caloric diet must be supplemented, however, by vitamins and other nutrients they might not otherwise get from their diminished diet. At a time when most mice are enfeebled from old age, and moribund, these mice are healthy and sexually active. If caloric restriction is started at birth, typically it produces a small animal; but it produces no other obvious bad effects. If the diet is started after physical maturity, there is no effect on size, although the ability to reproduce is diminished. In fact, this response to caloric restriction has developed through evolution as a way of dealing with famine. There is no point reproducing if there is not enough food to sustain the next generation. It is as if the animal has decided to live longer to wait for the famine to be over.
The general consensus is that caloric restriction is too difficult to be successful in human beings. People who eat very little are hungry all the time. Nevertheless, there are some who do stick to this diet. They are often researchers in this field, and they get satisfaction from knowing they are doing something that is too hard for most other people. Their immune system seems to function better with the result that they become ill less often and are less likely to develop cancer. Certainly they are less likely to develop diabetes and cardiac disease, which is known to be sensitive to diet. Their only complaint is of feeling cold most of the time.
Since the benefits of caloric restriction are mediated through chemical processes in the body, there are many groups currently investigating the possibility of finding the responsible physiological agents. It is thought that an ingredient in red wine may simulate the effects of caloric restriction. There are a number of other similar substances which, if successful, might be able to extend health and longevity in a way analogous to caloric restriction. But we are not there yet.
I agree that a diet which may be very healthy is not going to work if it requires someone to be hungry all the time over the course of a lifetime. A similar benefit can be obtained by eating low density foods. The “Stuff-Yourself Diet” emphasizes eating soups, salads and cereal. Soups and salads can be very low-caloric and taken in great amounts can eliminate hunger. Cereals can be higher in calories but are, nevertheless, useful because they are so filling.
Because of the evidence from studies of caloric restriction and other studies I think the healthiest weight is probably on the lower end of normal. This is controversial. Some more recent studies seem to suggest that people are healthier at the upper end of the normal weight range. I think these results are explained mostly by the fact that some of the people in these studies started off thin because they were already sick, although not obviously sick.
Too thin, though, is not good. Women who are so thin they have stopped menstruating are too thin. It is easy, too, to eat an unbalanced diet in pursuit of thinness. There are all sorts of problems that come from eating foods deficient in one nutritional factor or another.
There are two reasons why I hesitate to recommend that a dieter should aim for being on the thin side:
The goals of dieting and losing weight should be measured by the extent that someone has adhered to his or her diet over the course of a day or a week and by the exercise that person does over the course of a day or a week. What the scale says from day to day in unimportant. Whether someone is much closer or just a little closer to losing the weight they need to lose does not matter. On that basis whether the weight that someone has to lose is thirty pounds or fifty pounds does not matter. It is the way someone gets to his or her goal that counts in the long run. If the process of dieting can be made palatable (even enjoyable) the dieter will not gain back excessive weight in the future.(Excerpted in part from "The Stuff Yourself Diet.") Follow Dr. Neuman's blog at fredricneumanmd.com/blog/ or ask for advice at fredricneumanmd.com/blog/ask-dr-neuman-advice-column.