Could we have been wrong about exercise and weight loss?
In a thought-provoking article in New York Magazine, Gary Taubes reviews the evidence for exercise and weight loss and the relationship turns out to be far more complex than most of us thought.
For years, conventional wisdom held that you lose weight by exercising (and, of course, by eating less). These two cornerstones of dietary strategy were rarely questioned, and it wasn't really until Dr. Atkins introduced the hormone connection to weight that anyone seriously considered that the relationship could be a bit more complicated than just calories in, calories out. Taubes reviewed the evidence that exercise "causes" weight loss and finds it, to put it mildly, wanting. Sure, lean people exercise more than those who are not lean, but, as he pointedly asks, "Does that mean that working out will make a fat person lean?" The science, says Taubes, suggests that there's more to it.
Let's be clear. No one—including Taubes—suggests that exercise isn't a good thing to do. It has proven benefits on the cardiovascular system. It has proven benefits on the brain. (In fact, aerobic exercise actually can cause new brain mass to grow!) But as many people know all too well, simply going to the gym for 20 to 30 minutes (or more) three times a week (or more) won't always cut it when it comes to fat loss. The results have been sorely disappointing for more than a few people, probably causing them to give up and go back to their sedentary ways.
Taubes suggests a couple of other mechanisms that may illuminate the exercise-weight loss relationship. One is the fact that exercise increases the appetite, causing many people to eat a lot more after working out, thus blunting the calorie-burning effects of the exercise. A second is the fact that some people may be genetically programmed to "store" and others to "burn"—perhaps Lance Armstrong sits on his bike because his body is programmed to find ways to burn off excess energy, and perhaps Mr. Jones sits on his couch after dinner because his body is programmed to store that Big Mac. And third—and most convincing—is the activation during exercise of an enzyme known as LPL (lipoprotein lipase), which is responsible for pulling calories into muscle cells during a workout. While this works great when we're exercising, afterwards, LPL just keeps on doing its job, but shifts to importing calories into the fat cells, working to return to them any fat they may have lost by exercising.
But the central point Taubes makes is that the biggest barrier to weight loss (whether fueled by exercise or diet) is one that Atkins readers have been hearing about for several decades: Over-secretion of the fat-storing (and LPL raising!) hormone insulin. "Because insulin determines fat accumulation, it's quite possible that we get fat not because we eat too much or exercise too little but because we secrete too much insulin or because our insulin levels remain elevated far longer than might be ideal" Taubes concludes.
The take-home point isn't that we shouldn't bother to exercise. Of course, we should. But if we are turning to exercise primarily as a way to lose body fat, we'll get much better results if we follow the Atkins program of eating: Controlled carbohydrate consumption, low sugar, no refined carbohydrates foods, no trans-fats, more protein and more fiber. That way of eating is least likely to keep insulin levels raised, and much less likely to sabotage your exercise efforts.