Yesterday I saw this article in the Arizona Republic (from the LA Times) saying that the Journal of the American Medical Association released a new recommendation for women to exercise for 60 minutes per day every day in order to avoid gaining unwanted weight. Yahoo has the same basic story (from Reuters). I find the Yahoo article particularly offensive because it’s titled, “For women, battle of the buldge just got tougher”, as if the recommendations have changed how diet and exercise effect women’s body fat; and they have a picture of an obese woman in a bathing suit, as if someone reading the article might not know what a fat person looks like.
Whenever you see an article about any kind of scientific research, it’s best to skip to the actual science. Or in this case, “science.” From the Republic:
The study was based on surveys of more than 34,000 U.S. women who were, on average, age 54 at the start of the study. They reported their physical activity and body weight, as well as health factors such as smoking and menopausal status, over 13 years. On average, the women gained 5.7 pounds during the study.
What? They were 54 years old on average? That means the average age at the end was 67 (depending on who died). I don’t understand how or why they would derive recommendations for all women based on survey data from post-menopausal women. Nor do I understand how an average weight gain of less than half a pound per year is at all significant.
Only 13 percent of women in the study maintained a healthy weight throughout the study — and those who got an hour of exercise a day on average or more were by far the most likely to be in that group.
Something’s not right here if they all averaged a 13-year weight gain of 5.7 pounds while only 13% maintained a healthy weight. At this point, I’m inclined to dig into the actual numbers, but I’m not about to pay $15 for the privilege. Without getting into it, I can’t really tell, but it smells like the data do not fit the conclusion. I think what’s going on here is that current government recommendations (150 minutes of moderate exercise per week) aren’t working and instead of questioning whether exercise causes weight loss or prevents weight gain, the experts will just conclude that it’s not enough. This study is being used because it weakly shows the desired conclusion.
I’ve been convinced that exercise is not a reliable means of weight loss (or weight gain prevention) ever since reading this article by Gary Taubes:
There was a time when virtually no one believed exercise would help a person lose weight. Until the sixties, clinicians who treated obese and overweight patients dismissed the notion as naïve. When Russell Wilder, an obesity and diabetes specialist at the Mayo Clinic, lectured on obesity in 1932, he said his fat patients tended to lose more weight with bed rest, “while unusually strenuous physical exercise slows the rate of loss.”
The problem, as he and his contemporaries saw it, is that light exercise burns an insignificant number of calories, amounts that are undone by comparatively effortless changes in diet. In 1942, Louis Newburgh of the University of Michigan calculated that a 250-pound man expends only three calories climbing a flight of stairs—the equivalent of depriving himself of a quarter-teaspoon of sugar or a hundredth of an ounce of butter. “He will have to climb twenty flights of stairs to rid himself of the energy contained in one slice of bread!” Newburgh observed. So why not skip the stairs, skip the bread, and call it a day?
More-strenuous exercise, these physicians further argued, doesn’t help matters—because it works up an appetite. “Vigorous muscle exercise usually results in immediate demand for a large meal,” noted Hugo Rony of Northwestern University in his 1940 textbook, 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. Statistics show that the average daily caloric intake of lumberjacks is more than 5,000 calories, while that of tailors is only about 2,500 calories. Persons who change their occupation from light to heavy work or vice versa soon develop corresponding changes in their appetite.” If a tailor becomes a lumberjack and, by doing so, takes to eating like one, why assume that the same won’t happen, albeit on a lesser scale, to an overweight tailor who decides to work out like a lumberjack for an hour a day?
Credit for why we came to believe otherwise goes to one man, Jean Mayer…
It’s always one man.