Exercise Does Keep the Weight Down

The son of a famous French physiologist, JEAN MAYERcame to the United States before the war to pursue his studies; but the war called him home, and as a Gaullist he fought for five years with the Free French forces. He got a Ph.D. at Yale Medical School in 1948, a D.Sc. from the Sorbonne, and in 1950 joined the faculty of the Department of Nutrition at the Harvard School of Public Health, where his studies on obesity have attracted wide attention.



OBESITY has become a national obsession. Technical journals, newspapers, magazines, radio, and television daily dispense a barrage of propaganda. Much of this campaign is ineffectual. Occasionally it is harmful, because it is based on misstatements. Some of these are intentional mercenary lures, advertising “health foods” or ‟thinning foods.” Some are promises based on witchcraft (“Eat all you want and lose weight”).

Other inaccuracies are more serious yet, since they emanate from respected “experts.” Chief

among such pronouncements is the claim that exercise is of no value as a reducing aid.

The view that exercise expends relatively little energy is erroneous. If it were true, strenuous physical activity could be of only small importance in maintaining the balance between calorie intake and calorie outgo. This balance, of course, determines the extent of overweight. Another false idea is that, at any level of calorie intake, an increase of physical activity is automatically followed by an increase in appetite and is therefore self-defeating as a weight-control measure. The facts show that exercise is the great variable in energy expenditure and that exercise does not necessarily increase food intake. An increase in food intake follows an increase in exercise only under limited conditions.

The first misconception, the minimizing of the cost of physical activity, could be avoided by anyone who had occasion to look thoughtfully at a table of “Recommended Dietary Allowances” such as has been elaborated by the League of Nations, the United States National Research Council, and Other national and international agencies, For example, the daily allowances for men given by the National Research Council vary from 2400 calories for “sedentary” men to 4500 calories for ‟very active” men. Laborers, soldiers in the field, and athletes are advised by the NRC that they may require up to (and occasionally more than) 6000 calories. The range of 2400 to 6000 calories should dispel the myth that physical activity plays but a negligible role in the daily energy balance.

One of the most striking illustrations of what happens if you don’t compensate for the increased energy expenditure caused by physical activity is provided by the systematic studies made by the busy little nutritionists of the Third Reich. These happy hearts, while gallantly building for a thousand years, had set themselves the problem of finding out the degree of undernutrition compatible with continued production of coal by foreign miners impressed into service in the mines of the Ruhr. The Nazis discovered that it did not pay to try to reduce the intake of these prisoners to a level corresponding to that suitable for sedentary activities. The health of the victims disintegrated and their production fell to nothing—proof that steady physical activity consumes a perceptible quantity of calories.

And yet, how frequently we are exposed to assertions such as “A pound of fat can be worked off only by walking thirty-six hours, or splitting wood for seven hours, or playing volley ball for eleven hours.” The enemies of exercise visualize any given wearying performance as being accomplished in a single uninterrupted stretch. The energy expenditure accompanying physical activity takes place, however, whether the activity is performed in a day or a decade. Splitting wood for seven consecutive hours would be difficult for anyone other than Paul Bunyan, but splitting wood for half an hour a day — in no way an impossible assignment for a healthy man — will add up to the desired seven hours in a fortnight. If this thirty-minute lumbering operation represents a regular practice, it would be, according to the very reasoning of the foes of physical activity, calorically equivalent to 26 pounds of body fat a year. Similarly, a half hour per day of handball or squash would add up to, in the course of twelve months, a good 16 pounds of body fat.

Energy expenditure in most types of activity, where only parts of the body are moved, is directly proportional to body weight. A tennis player who weighs 150 pounds expends about one per cent of the cost of playing tennis in moving his racket, about 99 per cent in moving his body. In the case of a heavier man, expenditure would be proportionally greater. A 200-pound player going through the same movements would expend in work one third more than his 150-pound opponent. He will either lose more weight or need more food to cover the expense of his three sets than does the thin man. For the “mean” man, then, examples of energy expenditure per hour over that of sitting are: walking (not running), 100 to 550 calories, depending on the speed; swimming, up to 685 calories; skiing, up to 950; climbing, the same; skating, up to 685; and cycling, up to 585.

These hourly energy expenditures above the resting level of sitting are still lower than the peaks reached in athletic competition. For a sport like rowing such peaks may approach 1300 calories per hour. A caloric expenditure of 500 to 600 calories per hour above the resting level represents a degree of physical activity which can be endured by the average out-of-condition adult for a half hour without undue discomfort. A trained man should feel all the better after a full hour or more of such exercise. For those for whom translation into foods is more meaningful than caloric counts, the expenditure corresponding to thirty minutes of this kind of exercise is equivalent for our “mean” man to an average piece of pie decorated by a standard scoop of ice cream. Regular exercise, it becomes clear, can be a substitute for regular deprivation.

Moreover, if excess body weight is such that it impairs body movement, the cost of exercise will actually increase faster than does body weight. It follows that an overweight person will require more energy (and hence, unless fed more, burn a greater amount of body fat) for the same amount of exercise than will a person of normal weight. Twenty per cent overweight will increase the cost of walking, skiing, golfing, by at least 20 per cent, and it will increase the cost by more if the overweight makes the exerciser more clumsy and less efficient.

The dependence of the cost of physical activity on body weight has another important consequence. Any increase of calorie intake above the balance level will cause only a modest increase in weight in a physically active individual, because of the energy cost in moving the extra poundage. By contrast, in a sedentary individual, less energy will be expended moving the extra weight; weight gain, therefore, will be more rapid and more pronounced. If a Swiss mountaineer suddenly increases bis food intake by a moderate amount, he will quickly stabilize his weight. He will use up the increase to carry uphill the two or three pounds which he at first accumulates. His streetcaror auto-riding Zurich brother lacks such an automatic self-correcting mechanism. The latter may add five or ten pounds before the slow increase in heat loss (sometimes referred to as “increase in basal metabolism”) which follows the expansion of his waistline eventually starts matching the daily addition to his caloric consumption of, say, a dessert at supper. The active man has two brakes on weight gain: increased cost of exercise (a very potent one) and increased basal metabolism. The sedentary brother has only the less effective increased basal on which to rely, and he will curb his progressive fattening much more slowly.

Readers who are familiar with the conditioning of race horses and of boxers know that exercise, as much as or more than rationing, is relied upon to avoid overweight. By contrast, a constant universal practice in fattening young hogs, geese, or steers consists in restricting their activity by cooping them up in pens or tethering them. Whatever misguided “health educators” may preach, farmers all over the world agree that the first step in the production of lard or of pάté de foie gras is to prevent the producing animals from increasing their energy expenditure by unhampered wandering.


THE second widespread misconception, somewhat more difficult to dispel, is, regrettably, embodied in a proposition which not only sounds plausible but is also in part true. It is the oft-repeated allegation that exercise is of no value in weight reduction because an increase in physical activity always causes an increase in appetite and food intake which is at least as great in energy value as the energy expended in exercise.

That an increase in appetite follows an increase in activity in a normal animal or person is true enough. It explains why the weight of most adults is relatively constant. A fine adjustment of appetite prevents the body from burning away its substance when the individual is called upon to perform at a higher level of exertion than has been his custom. This adjustment of caloric intake to caloric expenditure admits of definite limitations even in a normal person. Energy expenditure must not be raised above a certain upper limit; it must not be lowered below a certain minimal limit.

These statements can be substantiated by observation of laboratory animals as well as of human beings. In the Nutrition Department at Harvard, my collaborators and I have studied the way the food intake of white rats varies when their exercise is varied. We used a motor-driven treadmill and accustomed a large group of rats to running on it. Then we divided the large group into a number of smaller groups, which were exercised, respectively, for one, two, three, up to ten hours daily; we measured their food intake during a few weeks of this regimen and their weights after it. Finally, we compared them with rats which had been left unexercised in their cages.

We learned that rats exercised one or two hours daily did not eat more than did the unexercised rats; indeed, they ate somewhat less. From two hours onward, increasing duration of exercise was accompanied by increasing food intake, up to a duration of eight hours of exercise, which represented the peak that rats could endure. Higher durations could not be maintained. The animals became exhausted, ate less, and lost weight. Swimming the rats, instead of running them, gave the same results.

The range of inactivity, in which decrease in food intake no longer responds to decrease in activity, can be truly termed the sedentary range. Above this comes the range of normal activity where appetite and exercise are attuned. Above the normal range is the exhaustion range, where an increase in activity is no longer followed by an increase in appetite but by a decrease. This last is obviously an unstable situation which cannot be endured indefinitely. Neither the sedentary nor the exhaustion range represents a normal mode of life. Animals are not meant to be caged. They are not designed to be pushed beyond the limits of what the body can stand. In the central zone, that of normal activity, appetite reveals itself as a sensitive and reliable mechanism for equating energy intake to energy expenditure.

Such conclusions, gathered from presumably reluctant rats, also apply to man. The sedentary range is presented in its extreme form by the studies of Dr. James H. Greene of Iowa City, who ‟collected” two hundred patients in whom the beginning of obesity could be traced directly to a sudden decrease in activity resulting from a change in occupation, blindness, fractures, and the like. A massive experiment immediately after the war, on millions of young men discharged from the active life of fighting units and “rehabilitated” in classrooms and offices, has perhaps not received enough attention. Returning veterans had a tendency to put on weight rapidly. This was not due exclusively to a return to home cooking and a peaceful atmosphere, but to a very sedentary life as well.

The role of decreased activity seems of particular importance in childhood obesity. Numerous articles and books have been written on why obese children eat more than non-obese: as an escape from tensions at home, as a substitute for the affection of one parent or of both, as a result of parental neglect or oversolicitousness, because of desire for importance, as a compensation for excessive shyness. But, although a few psychiatrists, such as Hide Bruch, have observed that obese children are often inactive, it is only recently that the basic assumption has really been questioned. Do obese children overeat, or do they get their surplus of calories from underexercising?

Penelope Peckos and Peggy Crooke Fry, two able nutritionists who studied Boston school children, concluded that lack of activity was the dominant feature in the development of obesity. The studies we conducted with Dr. Mary Louise Johnson, using high school girls from Newton and Brookline, Massachusetts, gave similar results. A very careful examination of the dietary intake of equal groups of overweight and normal-weight girls, matched for age and height, showed that the obese students fell into two groups. One, by far the larger, consisted of girls who ate a little less than the normalweight girls but who exercised considerably less. All the “sitting” activities were emphasized at the expense of walking and active sports. Watching television consumed four times as many hours in this group as it did in the normal-weight group. There was also a small group of active obese girls, who ate more than and exercised as much as the normal. This latter group, incidentally, was of the red-cheeked, cheerful variety. Dr. Johnson found that this group appeared more muscular, so that, while “overweight,” they were probably less “overfat ” than the inactive group.

All these findings inevitably bring us to the conclusion that, with respect to physical activity, obesity is in many instances truly a “disease of civilization.” Mechanization and the development of modern means of transportation combine to decrease physical exercise. For many individuals, physical activity is depressed to such an extent that the sedentary state is reached, and excessive calories accordingly accumulate as fat.

We eat less, probably, than our grandfathers did. The sight of an old-time wedding menu is enough to demonstrate this point. But, in order to get to the wedding, grandpa had to walk or ride horseback for long distances even in the dead of winter. Also, old-fashioned dancing was generally more strenuous than the modern variety. By the time our grandparents were home, they had expended a large part the surplus calories they had accumulated.

On a primitive farm, both the husband and the wife worked in the fields, plowing, hoeing, harvesting. The use of oxen for many of the farming operations imposed a slow rhythm on the farmer. As better plows and other improved implements became available and as tractors were introduced, the productivity of the farmer soared. Today he no longer requires the help of his wife for the heavy work of the fields; she has become a housewife, with perhaps only the relatively minor chores of a vegetable garden or the milking of cows and the care of rabbits or chickens. Meanwhile the physical expenditure of the farmer has hardly decreased; the new implements are heavy and continue to involve a lot of vigorous manual activity; driving a big tractor requires considerable muscular effort, and gone are the pauses at the end of the furrow. Now the farmer’s work is only slightly less arduous and it is much more continuous.

It is only when the degree of farm mechanization symbolized by, say, milking machines is reached that the energy expenditure of the farmer really drops. Meanwhile, if the appetite of the farm woman has declined too slowly, either because her activity has dropped into the nonresponsive sedentary zone or because customs and the necessity of still providing big meals for her menfolk have influenced her unduly, she has become fat.


IT is always a dangerous operation to tell modern suburbanized or urbanized women, young mothers or career girls, that in the physiologic sense of the term they don’t perform a great deal of work. It is prudent to add quickly that what is meant is that hard physical work and tiring activity are not necessarily synonymous. Most of the occupations of the modern active woman may be tiring, but they don’t involve a great deal of pushing, or of carrying considerable loads for long distances, or of picking up heavy objects several times a minute. Ironing and climbing stairs are perhaps typical of today’s common heavier expenditures. These involve, respectively, elevating repeatedly a 10-pound object and continuously (for a short period) the weight of the body. Although the care of several small children or, moving downtown, the strain of working for an exacting executive may be nerve-racking, it still does not compare with a day spent hoeing potatoes, as far as calories expended are concerned.

The result of all this is that, by and large, overestimates of the energy needs of women have been traditionally tremendous. In addition, caloric requirements of women were overestimated, because they were not measured on women, but were calculated for women. Several recent surveys in England, in Scotland, and in the Middle West, in which the caloric intake of normal-weight housewives and career women was determined, have shown that these women consumed only 1500 to 1900 calories, instead of the 2200 to 2400 calories which had been postulated for them. In our experience in Boston, the only women who ate what the textbooks and official tables prescribed for either sedentary or light activity were grossly overweight women who were getting rapidly more obese. Any woman who was conscientious enough to eat what is widely represented by nutritionists to be the ideal diet for the modern American woman would quickly find herself in this obese category.

There is one serious situation, as a matter of fact, where this dilemma arises; it is during pregnancy. To the normal diet, already overestimated calorically, are added, at least for the second half of the pregnancy, 300 or 400 calories for the growth of the baby. No second thought is given to the fact that, in Western societies at any rate, the mother’s physical activity is so far decreased during that latter period by rests and the slowness of her movements as to have already compensated, in large part, for her increased requirement.

The poor girl is nevertheless given a model diet, rich in milk, meat, eggs, butter, and warned of the terrible Consequences, for herself and for her child, of skimpy intakes. Further, she is weighed twice a month and threatened with even more terrible consequences, again for herself and for her child, if she puts on too much weight. In all this, the caloric intake of women is badly estimated, again fundamentally because of the lack of appreciation of the influence of exercise.

We — and nature will not permit us to forget this—are the sons (and daughters) of the cave man. For hundreds of thousands of years, natural selection succeeded in producing a group of tough, resourceful mammalians, who could roam the vast, empty stretches of wilderness, spend days in pursuit of herds of game, migrate from Central Asia to the shores of the Atlantic, cross deserts and climb mountains in search of a better environment, run for their lives before their enemies, remain on the go all day — sometimes, even, all night and all day.

We their children, modern Westerners, sleep all night in comfortable beds, ride to work, sit all day in front of our desks, or stand before our workbenches. We ride back home, sit before the dinner table, sit to read our papers and magazines, sit at a motion picture or in front of our television set and so to bed. We are using our bodies and their marvelous regulatory mechanism in a way for which they were never designed. Small wonder that, livnig thus on the fat of the land, so many of us become fat. The wonder is that, for many others, appetite does adjust to this extraordinary set of circumstances.

If we want to avoid obesity, we must either exercise more or feel hungry all our lives. To increase our exercising, we must be trained from youth in sports which we can pursue for a major part of the years ahead; typical of these are tennis, swimming, and mountain climbing. This necessary training requires a major reorientation of the athletic programs of our schools, and a multiplication of the generally inadequate facilities for adult exercise. The results will be worth the havoc visited upon our habits. We will be able to keep trim and hard — instead of being either obese and flabby or thin, flabby, and starved.

In the August Atlantic we shall publish a second article by Dr. Mayer, drawing the distinction between overweight and obesity.