There’s an old joke lumberjacks still love to tell:
“Why did the train stop?”
Answer: “To let the lumberjack off.”
This quip was coined around the same time that a famous study was conducted. It was a study that measured the caloric intake of lumberjacks, whose appetites are about as notorious as the size of their logs.
It turns out that the caloric intake of a lumberjack is, on average, about 5,000 calories per day.
By comparison, this same study measured the caloric intake of tailors. Tailors, it turns out, consume on average half that: 2,500 calories per day.
It was found in addition that those who change their occupation from light to heavy work, or vice-versa, develop corresponding changes in appetite.
All of which is by way of saying that physical activity makes you hungry. Not exactly news, and yet if it’s followed to its conclusion, the ramifications run deep.
The relationship between weight loss and exercise is a complex relationship, and no matter what anyone tells you, it is not well-understood.
Furthermore, despite prevailing wisdom, despite what you’ve been hammered with all your life, there’s not a shred of real evidence that suggests exercise promotes significant weight loss. As a matter of fact, at one time not so very long ago — up until 1962, to be precise — the medical prescription for obesity was bed rest.
An obesity and diabetes specialist named Russell Wilder, of the Mayo Clinic, lectured famously in 1932 on obesity. Among other things, Mr. Wilder told us that his “fat patients lost more weight with bed rest,” while “unusually strenuous physical exercise slows the rate of weight loss” (Russell Wilder, 1932).
As Wilder and his colleagues reckoned it, “Light exercise burns an insignificant number of calories — amounts that are undone by comparatively effortless changes in diet.”
A University of Michigan researcher named Louis Newburgh calculated, in 1942, that the average man “expends only three calories climbing a flight of stairs. He will have to climb 20 flights of stairs to rid himself of the energy contained in one slice of bread.”
Why then, ask some, don’t we simply skip the stairs and skip the bread? It’s a good question.
These physicians argued that the more taxing the physical activity, the more that the appetite increases. And study after study, beginning with those conducted on our previously mentioned lumberjacks and tailors, confirm this.
“Vigorous muscle exercise usually results in immediate demand for a large meal,” said Hugo Rony (not to be confused with Rice-a-Roni, the San Francisco treat), in a 1940 textbook titled Obesity and Leanness. “Consistently high or low energy expenditures result in consistently high or low levels of appetite. Thus men doing heavy physical work spontaneously eat more than men engaged in sedentary occupations.”
Mr. Rony here goes on to speak of our flapjack-eating lumberjacks, and ends, curiously enough, by asking the same question these men repeatedly asked him:
“Why did the train stop?”
Of course, the real question is not why the train did or didn’t stop, but why we’ve come to believe — and believe so overwhelmingly — the exact opposite of what was once the prevailing medical view?
Credit for that belongs to one Jean Mayer, initially of Harvard University, who then went on to become America’s most influential nutritionist.
As an authority on human-weight regulation, Mayer was among the very first of a new breed, a type that has since come to dominate the field. His predecessors — Wilder, Rony, Newburgh and others — had all been physicians who worked closely with obese and overweight patients. Mayer was not. His training was in physiological chemistry; he had obtained a doctorate at Yale with a dissertation on the interrelationship of vitamins A and C in rats. In the ensuing decades, he would publish hundreds of papers on different aspects of nutrition, including why we get fat, but he never had to reduce obese patients as part of his clinical obligation, and so his hypotheses were less fettered by anecdotal or real-life experience.
As early as 1953, after just a few years of research on laboratory mice, Mayer began extolling the virtues of exercise for weight control. By 1959, the New York Times was crediting him with having “debunked the popular theories” that exercise played little role in weight control. Mayer knew the obese often eat no more than the lean and occasionally even less. This seemed to exclude gluttony as a cause of their weight gain, which meant that these fat people had to be less physically active. Otherwise, how could they take in more calories than they expend and so become fat?
Through the sixties, Mayer documented the relationship between inactivity and the overweight. He noted that fat high-school girls ate “several hundred calories less” than lean classmates. “The laws of thermodynamics were, however, not flouted by this finding,” he wrote, because the obese girls expended less energy than the lean. They were much less active; they spent four times as many hours watching television. Mayer also studied infants. “The striking phenomenon is that the fatter babies were quiet, placid babies that had moderate intake,” Mayer reported, “whereas the babies who had the highest intake tended to be very thin babies, cried a lot, moved a lot, and became very tense.” Thus, Mayer concluded, “some individuals are born very quiet, inactive, and placid and with moderate intake get fat, and some individuals from the very beginning are very active and do not get particularly fat even with high intakes” (Gary Taubes, “We Can’t Work it Out”).
Jean Mayer pioneered the exercise and weight-loss practices that many people today consider axiomatic.
Jean Mayer cited “sedentary living” as the “most important factor” in obesity, and, for that matter, all other adverse health conditions appertaining thereunto.
“Modern people,” said Mayer, “are inert compared with their ancestors [who were] constantly engaged in hard physical labor…. The development of obesity is to a large extent the result of the lack of foresight of a civilisation [sic] which spends billions annually on cars, but is unwilling to include a swimming pool and tennis courts in the plans of every school” (Jean Mayer, 1968).
At that time, many doctors and nutritionists disagreed with Mayer’s pronouncements; and even now, a number of very reputable scientists still do.
“It is a common observation that many obese persons are lazy, i.e. they show decreased impulse to muscle activity. This may be, in part, an effect that excess weight would have on the activity impulse of any normal person” (Rony, 1941).
But isn’t it equally possible that obesity and physical inactivity are symptoms of the same cause?
And isn’t it obvious that the more physically active we are, the hungrier we get?
Mayer’s voracious attack on hunger completely masked the logical inconsistencies his arguments contain.
He did at one point acknowledge that “exercise could make us hungrier,” but in the same breath added “It wasn’t necessarily the case.”
This was the crux of Mayer’s nutritional philosophy.
He alleged a gap in the relationship between appetite and physical activity.
“If,” said Mayer, “exercise is decreased below a certain point, food intake no longer decreases. In other words, walking 30 minutes a day may be equivalent to four slices of bread, but if you don’t walk the half-hour, you still want to eat the four slices.”
This is untrue. And it’s the fatal flaw in his theory. As the lumberjack-tailor study makes very clear, physical activity has a direct and significant bearing on appetite.
And yet from his faulty premise, Mayer, unaware that he was upending the existing worldview on weight loss, wattled forward.
He based this conclusion on two (and only two) of his own studies from the mid-Fifties. The first purported to demonstrate that laboratory rats exercised for a few hours every day will eat less than rats that don’t exercise at all. But this was never replicated. In more recent experiments, the more rats run the more rats eat; weight remains unchanged. And when rats are retired from these exercise programmes, [sic] they eat more than ever and gain weight with age more rapidly than rats that were allowed to remain sedentary. With hamsters and gerbils, exercise increases body weight and body-fat percentage. So exercising makes these particular rodents fatter, not leaner.
Mayer’s second study was an assessment of the diet, physical activity and weights of workers and merchants at a mill in West Bengal, India. This article is still commonly cited as perhaps the only existing evidence that physical activity and appetite do not necessarily go hand in hand. But it, too, has never been replicated, despite (or perhaps because of) a half-century of improvements in methods of assessing diet and energy expenditure in humans. It helped that Mayer promoted his pro-exercise message with a fervor akin to a moral crusade (Gary Taubes, “We Can’t Work it Out”).
In 1977, coinciding with Mayer’s crusade, the New York Times spoke of the “exercise explosion” that had come about because the conventional wisdom of the sixties that exercise was “bad for you” had been transformed into the “new conventional wisdom — that strenuous exercise is good for you.”
The Washington Post as well estimated that “100 million Americans were partaking in the new fitness revolution” — coincident with the start of the current obesity epidemic.
Still, no matter how many billions believe it, the evidence that exercise promotes weight loss has simply never been produced.
My favorite study of the effect of physical activity on weight loss was published in 1989 by a team of Danish researchers. Over the course of 18 months the Danes trained non-athletes to run a marathon. At the end of this training period, the 18 men in the study had lost an average of 5lb of body fat. As for the nine women subjects, the Danes reported, ‘no change in body composition was observed’. That same year, F Xavier Pi-Sunyer reviewed the studies on exercise and weight, and his conclusion was identical to that of the Finnish review’s 11 years later: ‘Decreases, increases, and no changes in body weight and body composition have been observed,’ Pi-Sunyer reported (Ibid).
Here’s the main thing to realize: the relationship between exercise and diet is a complicated relationship, but the chemistry behind weight loss is not complicated:
To lose weight, you must simply use more calories per day than you take in. That’s it.
All the hype and all the fad diets and all the panaceas in the world won’t change that. Exercise does burn calories (even if it’s not quite as many as people think), but it also dramatically increases appetite. Thus, as often as not, exercise tips the scales in the wrong direction.
That’s the fact, Jack.
