Last week, Ezra Klein accused me of not having talked to more than a handful of obesity experts. Alas, had he done a little googling, he could easily have discovered that I was interviewing public health experts about obesity back when he was, by my count, finishing up Freshman comp. I've paid quite a bit of attention to the subject over the years, and over the years I've changed my mind about it quite a bit, in part because some of the science has changed, and in part because I've looked at different science. I don't agree with Paul Campos about everything, but I do agree with some of his core propositions:
- There is evidence to show that this is physiologic rather than pyschological--it is nearly impossible for very heavy people to simply "eat less and exercise more" to a "normal" weight (given that 2/3 of the country is overweight or obese, normal weights, aren't.)
- The fact that this often operates through the appetite system does not mean it's "all in their heads" or a lack of willpower. Appetite is a signal as powerful as thirst or pain. Most people can't ignore it.
- The largest environmental determinant of this trend is probably simply cheaper, tastier calories, which will be very hard to reverse
-Much of the panic about the obseity epidemic comes from lumping all weights together--everyone over a BMI of 30 becomes an obese people with high relative risks for various diseases, even though the whatever health risks exist among the lower overweight ranges are not anything like the dire health effects of morbid obesity
- At the moment, it's unclear whether there are any adverse health effects associated with overweight or even mild obesity, and to the extent that there are adverse effects, it is also unclear whether they are a result of the body fat, or a proxy for fitness levels and eating habits
- The emphasis on the visible proxy (obesity) is counterproductive in promoting healthier eating and exercise. Health has simply been approximated as a euphemism used by those pursuing society's ever-more-unrealistic expectations about weight. No matter what they say about being healthy, most people exercise to get thinner/more cut. If they don't get thinner, they may give up.
- The emphasis on the visible proxy may actually encourage counterproductive behavior. Upper class young women still smoke to stay thin (or go back when they gain post-quitting pounds); people take dangerous diet pills. There is some evidence that weight cycling (yo-yo dieting) leads to higher mortality, either directly, or because it increases your likelihood of becoming morbidly obese.
- The difference in observable mortality between people fifteen pounds apart (which seems to be at the edge of sustainable weight loss) is not large enough to merit either the hysterical headlines about America's weight gain, or really even dieting unless you're already afflicted with diabetes and heart disease.
I'm also convinced that obesity researchers often offer conclusions that are oddly at variance with the tone of their papers. Take this paper on weight cycling, which summarizes much of the literature regarding weight cycling, acknowledging both papers that say it adversely impacts mortality, and papers arguing that those papers suck. The paper says the evidence is equivocal, though it asserts that whatever effect weight cycling has on mortality probably comes because those who diet and regain end up gaining more weight than those who don't.
To me, that screams "do more research!" But the researchers couldn't . . . quite . . . bring themselves . . . to suggest that we might want to look into this further before continuing to recommend that people go on highly restrictive diets that they probably won't stick to.
More in general, the majority of epidemiologic studies on weight cycling and mortality have been carried out on either non-obese or only mildly obese subjects; the two studies that stratified sample by BMI showed that weight variability was more strongly related to mortality in lean than in obese subjects.4,6 Therefore, weight cycling may not have significant effects in a sample of obese subjects, about half of whom were morbidly obese, like the sample in the present study.
In conclusion, the present study shows that when examining the various components of weight cycling separately, weight loss has no adverse effects on cardiovascular risk factors that are associated with weight regain. Thus, patients should not be discouraged from trying to lose weight as for claims from the lay press,21 but the importance of avoiding weight regain should be stressed.
So we shouldn't tell people to stop dieting--we should tell them to stop regaining the weight! Why . . . it's so simple! How could we have missed it?
If 99% of the time the actual result of the course of action you recommend is that people diet, and then regain a bunch of weight, you need to take this into account before issuing further such recommendations. It doesn't seem like simply proclaiming that they shouldn't go and gain the weight back again is quite enough.
After all, people who have lost a bunch of weight are presumably aware of how they did it (and if not, they need to talk to an oncologist, not an obesity researcher). They are thus presumably also aware of what will cause them to gain it back. Nor are they usually uninterested in staying thin. They've usually worked very, very hard to lose all that weight, and are really quite desperate not to gain it back again. The idea that all that was missing was a doctor telling them that no, seriously, they should really keep that weight off--an incentive obviously far more powerful than, say, the horrific way that America treats fat people--has sailed beyond arrogant into fantasyland.