How do you determine what is the optimum weight for a person? It's probably different for people of different heights, so you could hold beauty contests for people in different height groups, and consider the winners to be of optimum weight. However, I'm sure that you'd find that the judges would be unable to disregard other differences between the contestants, so that it would be impossible to get answers that would be widely acceptable. It would be better to use some measure of health to arrive at an optimum weight, but it would be hard to get a generally acceptable measure, since the values of some measures of health would vary differently than would the values of others. Probably the best generally acceptable measure would be longevity. You could reasonably consider the optimum weight to be that weight which is conducive to the longest life. Of course, you would have to take height and build into consideration because the optimal weight seems likely to be different for people of different heights and build.
That's what the Metropolitan Life Insurance Company did in 1943 when they published what became widely-used tables of "desirable", i.e. lowest-mortality-rate, weights for men and women aged 25 to 59 and of various heights. The subjects had taken life-insurance exams fully dressed, so the heights in the tables were considered to include one inch contributed by shoes and the weights were considered to include three pounds of clothing for women, five for men. The data were divided into columns for people with small, medium or large frames, based on the width of the bones at the elbow (different values used for men and women). Collection of the data was not done in a rigorously scientific manner: frame size was sometimes estimated by eye, and some of the other data were sometimes obtained by questionnaire rather than measurement.
Inspecting these tables, Reubin Andres was struck with the fact that people of different ages were all lumped together to get the data. What if the ideal weights varied according to age? To find out whether or not this was true, he examined the same data that had been used to construct the tables, but made separate analyses for men and women in different decades of life. What he found and reported in his book (Principles of Geriatric Medicine, Reubin Andres et al. McGraw-Hill (1985) pp. 311 ff) was that the optimal weight (remember, we're talking about mortality, not winning beauty contests) increased as one got older. He also found that the optimal weights as he determined them were very similar for men and women. In the Metropolitan Life charts, considerably lower optimal weights are given for women.
Having to tabulate both height and weight is inconvenient, and studies of optimal weight now avoid this by using a mathematical trick. Instead of recording heights and weights, a composite index called the body mass index (BMI) is used. This is a measure of weight divided by height squared, and would be a good measure of overweight if every body contained the same percentage of fat. However, women's bodies in general contain more fat than men's bodies, and there is great individual variation in body fat content, particularly in women. Since fat has a lower density than other body constituents, it affects the BMI differently than does an equivalent volume of other body constituents such as water, protein and bone. Moreover, the effect of body fat on mortality seems to be a function of its location in the body, with fat occurring in the abdominal area or above associated with hypertension and other undesirable conditions, while fat distributed primarily in the lower part of the body is relatively benign. Thus, although a 200-pound person who is six feet, three inches tall, and a 150-pound person who is 5 feet, six inches tall both have BMIs of about 25, they don't really represent similar mortality risks.
However, that's how the data are presented in the medical literature, so, until we have the resources to undertake original studies, let's see what's in the literature, but maintain a skeptical view of what's presented.
Another reason a skeptical view is warranted is that the data in some papers presented in medical journals are presented in such a way as to suggest that the authors are operating with a presumption that overweight is a bad thing and that their task is to demonstrate that this is so. I'd like to present two pieces of evidence for this. The first is a paper published in The New England Journal of Medicine in 2003 (Calle, E. E. et al. "Overweight, Obesity, and Mortality from Cancer in a Prospectively Studied Cohort of U.S. Adults." The New England Journal of Medicine 348:17 1625-38 (2003)). The title page lists "Conclusions" and this reads, in its entirety: "Increased body weight was associated with increased death rates for all cancers combined and for cancers at multiple specific sites." However, a glance at the data showing the relative risk of men of different body mass indices dying from cancer shows that the risk is lower for men with a BMI in the range of 25.0 to 29.9 (considered "overweight") than in men with a BMI which is lower (considered "normal") or higher (considered "obese") than this. Since the vast majority of subjects were in the "normal" or "overweight" groups, increased body weight in men (alas, not in women) was shown by this study to be associated with decreased death rates for all cancers combined. This was acknowledged by the Journal printing my letter in a subsequent issue (see Deutsch, M. E. "Obesity and Cancer." The New England Journal of Medicine 349(5): 502-4 (2003)).
There's something else we should consider. Since it appears that we all must die from something, maybe the apparent protective effect of "overweight" on cancer in men is caused by "overweight" increasing their chance of dying from something else, such as heart disease, and the apparent increase in cancer deaths in "overweight" women is a result of their reduced susceptibility to some other cause of mortality, such as heart disease. In our quest to determine optimum weight or BMI with respect to mortality, we must look for studies which report on total mortality.
Now let us consider a paper whose results suggest that what is now considered to be overweight should be considered normal weight for both men and women. Once again, you wouldn't know it from reading the misleading title or the paragraph entitled "Conclusions," but here, at least, you can determine the truth by reading the paragraph entitled "Results" on the front page.
This paper (Flegal, K. M. et al. "Excess Deaths Associated With Underweight, Overweight, and Obesity." JAMA 293: 1861–7 (2005) appeared last year in the Journal of the American Medical Association and it described studies of the relative death rates of subjects who were underweight, so-called "normal" (BMI between 18.5 and 25), overweight (what was referred to as grade 1 overweight in the previous paper) and obese (what the previous authors called grade 2 and higher overweight). As promised by the title, the authors provide estimates of the excess deaths associated with having a body-mass index not in the "normal" range, but the title (and the conclusions) are a bit misleading, since the excess deaths associated with being in the overweight group are a negative number. That's right, they found that there were 86,094 fewer deaths in the overweight group than in the same number of subjects in the "normal" group. If you define normal as the group with the lowest mortality, then you should award this title to the group they call overweight. You would not be able to come to this conclusion reading the title and conclusions, and it is only grudgingly and indirectly admitted in the results paragraph by the statement "Overweight was not associated with excess mortality." That's correct, of course. It's associated with lower mortality.
Okay, I've presented evidence, provided by investigators reluctant or unwilling to admit what is shown by their data, showing that the optimal range of BMI (for maximum longevity) is not the generally accepted normal range, but the internationally accepted "grade 1 overweight" range of 25 to 30. Before going on to suggest how one might achieve an optimal BMI and presumably an optimal weight (that is, one conducive to maximal longevity) I'd like to point why I am pleased that I've obtained my data from authors who have arrived at conclusions not concordant with mine.
The double-blind collection of data is widely used because many studies have shown that investigators unconsciously affect the data they collect. They may "accidentally" record an expected number rather than the one actually observed. They may even unconsciously reveal to experimental subjects (even to rats!) what they want them to show, and the experimental subjects may provide what is wanted, also unconsciously. The studies I have just referred to, however, would be hard to perform in a double blind manner, so this wasn't done. However, the fact that we were able to draw from the data conclusions which were apparently opposite to what the authors expected or desired suggests that these unconscious distortions of the data did not take place and that we should give more weight to the conclusions I have drawn than to the conclusions of other authors who have found what they wanted or expected to find.
Now for what you really wanted to find out from reading this article: what should you eat to achieve and maintain an optimal weight?
Sorry, that's the wrong question.
Like everything else about you, your appetite has been fine-tuned by evolution. Like all other animals, we have been shaped by evolution to seek out as food what seems palatable to us and to eat it in amounts which satisfy our hunger and optimize our life span. Unlike other animals, we subject foods to artificial processing, which I define as separating the palatability of food (which evolution has taught us to seek) from the nutrients of the food (which are the reason that the sought-after food has led to our thriving and passing on life-sustaining tastes to our descendants). And just as squirrels would not thrive on peanut-flavored sawdust, we cannot thrive on foods which lack the nutrients we need but mimic their palatability. As for the macronutrients, protein, fat and carbohydrates, which provide us with the calories we need, I would like to point out that there are many essential amino acids and essential fats, but no essential carbohydrates. The Inuit have demonstrated that people can live on a largely carbohydrate-free diet and Vilhjalmur Stefansson has demonstrated that this is possible by doing so under carefully controlled conditions on a hospital ward. But excess carbohydrate in the diet can lead to the metabolic syndrome or diabetes, while excess fat and protein are essentially harmless, except for the trans fats which occur in only tiny amounts in nature. So the next question is "Has evolution, which has resulted in our having tastes which direct us to the correct foods for maintenance of optimal health (if we don't mess up the system by artificial processing of foods), also directed us to having appetites which direct us to eating the amounts of these foods which will result in optimal weight and optimal lifespan?" And the answer is yes, if a certain condition is met.
Let us first consider experiments which were performed on rats. They have shorter lifespans than people do and they are easier to control and to obtain in genetically uniform groups. We'll get to people later. First let us consider an experiment carried out by the late Jean Mayer and described in his book Overweight, Causes, Cost and Control (Prentice-Hall (1968) pp. 73–74).
Jean Mayer kept rats in cages containing motorized exercise wheels, and allowed them to eat as much as they wanted, but forced them to exercise for various lengths of time. He found that rats which exercised less that one hour a day ate amounts of food which were inversely proportional to the amount of exercise they performed. And these rats had weights which were inversely proportional to the amount of exercise they took However, rats which exercised from one to six hours a day ate in proportion to the amount of exercise they got, and their weights were independent of the amount of exercise they got.
In other words, the curve relating length of time exercising (up to six hours a day) to amount eaten was shaped like a check mark, with the minimum at one hour of exercise a day. The poor rats forced to exercise more than six hours a day lost weight because they were too tired to eat.
So here's some advice for rats. Exercise from one to six hours a day and your appetite will lead you to eat what evolution has found to be the optimum amount of food, which presumably leads to optimum longevity. However, note that if you are a lazy rat (less than one hour a day on the wheel) and want to lose weight so that you weigh the same as the exercising rats, you will always be hungry. This is also true if an experimenter restricts your diet and doesn't provide exercise facilities for you. This might get your weight and longevity into the normal range, but provides no useful data for those interested in having optimal weight and an enjoyable and long life. These data also suggest why studies have shown that rats kept in cages which provide no exercise facilities live longer if their access to food is restricted, and suggests that this might not apply to rats which exercise for an hour a day or more.
People are more variable and less controllable than laboratory rats, but Dr. Mayer found a way to duplicate part of his curves with people. He found an Indian railway construction site which employed a variety of workers whose work required the expenditure of different amounts of calories, and who brought their food with them to the work site, so that he could estimate their caloric intake.
He was able to duplicate the beginning of the rat curve, but none of the Indian workers worked so hard that he failed to eat enough to maintain his body weight. Sedentary workers and workers in the groups performing light work ate amounts inversely related to their dietary needs, and like rats exercising less than an hour a day had body weights which were inversely related to the amount of work they did and directly proportional to their caloric intake. However, for all workers in six groups which expended larger amounts of energy, caloric intake was proportional to caloric needs and body weight was a constant value independent of caloric intake (This study was made before BMI was used for such studies. However, the groups seem to have been large enough to minimize errors owing to height differences.) Note that these workers, like the experimental rats, ate as much as they wanted to eat.
So there's your answer. Expend as much energy as an Indian railway mechanic and eat as much as you want to eat and you will maintain the body weight which evolution has found to be optimum – the body weight associated with maximum longevity. The only caveat is to avoid foods which have been artificially processed in the sense of nutritive value having been divorced from palatability.
But wait! Suppose you can't get a job on an Indian railway project. There's other evidence which suggests that the minimum exercise amount to get you on the upward curving portion of the curve is twenty minutes of hard-breathing heart-thumping exercise at least three times a week. This is called aerobic exercise to distinguish it from anaerobic exercise, which is so intense that it can't be carried out for more than minutes at a time. Longer periods of exercise are better, but their effect on appetite will simply be to make you want to consume more calories to replace the ones you worked off. I don't think that I have to warn you not to exercise so much that you're too tired to eat. And the right question is, of course, "How much should I exercise to maintain an optimal body weight?"
July 27, 2006
