Secret Workout Routine: No, Exercise Really Can't Reduce Obesity
RealClearScience assistant editor and nutritionist Ross Pomeroy "strongly disagrees" with the argument I put forward in my most recent piece. Exercise, Pomeroy says, deserves its status as a weight loss tool. He makes several interesting points which deserve a response, but he's ultimately wrong. So here's a brief breakdown of each of his arguments.
Pomeroy begins his response by noting that my primary sources are all advocates of a low-carbohydrate diet. I'm not sure what his point is here, but I'll just note that three of the people I cited are physicians and the fourth (Taubes) has a physics degree from Harvard, and has spent 10 years writing about obesity. They all know what they're talking about, in case anybody is wondering.
Nonetheless, perhaps they're wrong, and Pomeroy cites some research which suggests that that's the case. A 1995 meta-analysis, for example, found that men participating in 28 different studies lost nearly 7lbs in 7 months (women lost even less) by engaging in regular aerobic exercise, without dietary restrictions. Response: big deal. Such an insignificant amount of weight loss would hardly make a dent in an obese individual's BMI.
Furthermore, multiple studies have demonstrated that diet and regular exercise may result in weight loss, but most people regain all of the lost weight, because the effects of calorie restriction and exercise are offset by a series of "metabolic, behavioral, neuroendocrine and autonomic responses," as one study put it. That should not be happening if exercise is so useful to dieters--hence my comment about an unworkable solution to obesity.
Pomeroy also calls my suggestion that exercise promotes hunger "distorted." But this point is also supported by plenty of clinical research, discussed in the New York Magazine article I cited in my piece. Exercise promotes hunger because our fat tissue wants to replace the calories that were given up to fuel the exercise we just engaged in. Following an hour at the gym or a long walk, this metabolic urge to eat occurs because an enzyme called lipoprotein lipase "works to return to the fat cells any fat they might have had to surrender...Our fat tissue is devoting itself to restoring calories as fat, depriving other tissues and organs of the fuel they need and triggering a compensatory impulse to eat." And since most people regain their lost weight, this response is certainly enough to replace the calories expended during exercise, contrary to Pomeroy's argument.
I also claimed, relying on four published trials, that endurance exercise can decrease resting metabolic rate, at least in overweight people. Pomeroy argued that this is likely false in the long term because "a habitual exercise program featuring resistance training may boost resting metabolism." But the sources I cited took this effect into account, and the reduced metabolic rate was observed despite the energy expenditure required to build and maintain muscle mass. More importantly, however, the research on this subject is contradictory, which means people don't all respond in the same fashion to exercise. And since that's the case, why do so many health authorities put so much emphasis on exercise as an anti-fat measure?
The truth is that (and Pomeroy concedes this as well) we really don't know how exercise affects everybody. As someone who tried and failed to lose weight following the boilerplate "eat less, move more" nutrition advice, all I want is for everybody to admit it.