I’ve expressed skepticism in the past than any amount of exercise, short of an hour or more per day, will contribute to weight loss.
The main reason for this is that, as we exercise, our body tends to make us hungrier than we used to be, so that we make up for the calories consumed during exercise by simply eating more. On the balance, we don’t end up burning more than we eat, and our weight tends to stay even. Gary Taubes, author of Good Calories, Bad Calories, is a leading proponent of this view, and it’s easy to buy into this view when you exercise periodically and don’t lose weight.
But obviously, if we exercise enough, we do lose weight. Watch some Olympics soccer, and you won’t find anyone remotely heavy (unlike in sports like baseball where less exercise is required). Try training an hour to an hour and a half a day for a marathon or triathlon and you’ll also find it hard to keep up the weight you maintained before you started training.
My theory on this, though, was that you simply burn so many calories exercising this way that you don’t have enough time in the day, or tolerance for eating so much food, to get enough calories back in your body to make up for it.
But there are many reasons why I may well have been wrong in my theory on exercise. It may be far more effective than I’d thought. Here are some main reasons why:
1. Diets like Atkins, Ornish, raw and Paleo have made us accustomed to very rapid weight loss. Try any of these diets and, depending on what your diet was beforehand, you’re likely to lose five or more pounds in as little as a week.
Start exercising alone, and this is unlikely to happen.
The reason is, losing weight by exercising happens very slowly. And this is because truly losing weight happens very slowly. The body has to burn 3500 more calories than it consumes, in order to lose one pound of body weight. (The opposite goes for weight gain.) Since the typical American may eat only 2000 to 2500 calories per day, we’re not going to lose 5 pounds of true weight in one week even by eating zero calories per day. The math simply doesn’t add up.
So, how do you lose 5 pounds in one week on those other diets? Most of this initial weight loss is likely a drop in water weight (the modern American diet tends to cause us to retain more water than we should) and/or a drop in the amount of excretory matter we retain at any time (again, the modern American diet tends to retard normal bowel function). Because these diets resolve these modern issues very quickly, we see a big change right away on the scale.
But the true weight loss–the burning of excess retained fat–happens much, much more slowly. Just think: if you normally consume 2500 calories per day, and you cut that by a striking 20%, it’ll still take you a full week to lose just one pound. Most of us are unlikely to cut our calorie consumption even that drastically.
So, if you start exercising, and you don’t see a significant jump on the scale, as you would on any of these other diets, you tend to think exercise isn’t working, for weight loss. It may well be if you stay patient.
2. Exercise may also cause us to eat worse foods. I know that on a day when I run 8 miles I’m much more likely to eat foods that are not on my ideal diet. When I run 15, I’m much more likely to eat foods that I normally wouldn’t even dream of consuming. This deterioration in dietary quality can also tend to slow weight loss from exercise, and make us question whether it’s possible. But that’s really not exercise’s fault: if you recognize that you still shouldn’t eat bad foods, and you maintain the normal quality of your diet, you may well see meaningful weight loss from exercise.
3. My assumption that our bodies would want to make up for the calories lost through exercise, making us hungry so that we consume those extra calories, may be mistakenly based on the idea that we eat because we want calories.
Obviously, we need calories in order to undertake our daily tasks. Even breathing consumes calories. But we need more than just calories. We need vitamins and minerals and untold other nutritional compounds, like antioxidants, that we need to get from our food. And we may well simply be hungry until we get enough of these nutrients, rather than enough calories.
And while exercising may burn calories very quickly, it may not cause our bodies to use up nutrients as quickly. And so our bodies may not be as much hungrier for nutrients after exercise as it would be if it cared primarily about calories. So we may not end up eating as many additional calories after exercise as we would if our bodies got hungry primarily for calories rather than nutrients.
4. Finally: There’s a possibility that as we exercise more, our body starts to recognize that it needs to be ready for that exercise, and prefer a lean, athletic form. There’s no question that your body goes through changes when you exercise regularly. My arms are much thinner, and firmer, two months into marathon training, than they were when I was sitting around all day and exercising very little. And I’m barely even using those arms during training: certainly, marathon running doesn’t exercise my wrists so much that my forearms should have gotten so much more wiry.
So it may be that my body, recognizing the need for leanness if it wants to carry out my lengthy runs each day, tells me to not be so hungry and not eat so darned much, if I want to be in optimal shape to carry out my daily regimen: exercise may actually be programming my body to “think thin.”
So I’m rethinking my take on exercise. My current marathon training has contributed to this significantly, since I’ve already lost several pounds during training, without ever going hungry or trying to eat differently. (In fact, I’m even eating lower quality foods that would tend toward weight gain, largely because my heavily increased caloric demands have been tough for me to fulfill on the exclusively raw vegan diet I prefer.)
This experience may not be the best one on which to base a shift in philosophy toward exercise, because it involves an hour and a half a day of running, and so also fits into my earlier theory of burning so many calories there’s not enough time in the day to make up for it.
But the way my body looks and feels, it doesn’t seem that I’m simply starving myself, depriving myself of the necessary calories because there isn’t enough time in the day to eat them. Something else is going on, and I think it’s healthier than that. And I’m not sure I’d have to run an hour and a half every day to realize those results. Surely, I’d see less significant results if I cut my exercise regimen back significantly, but I’m guessing that, contrary to my earlier belief, even a half hour a day of exercise would have a meaningful impact on weight. This is a big shift from my earlier thinking.
Of course, weight loss isn’t a perfect measure of health, even when it comes to one individual’s own relative weight over time. We’ve all heard stories of skinny people getting heart attacks (see Malcolm Gladwell’s recent piece on former marathoner Alberto Salazar) or cancer. Surely, exercise alone doesn’t seem to be enough to make up for a questionable diet. (It’s hard to ever know what diet skinny people who have heart attacks followed, but I wouldn’t be surprised if it typically involves regular consumption of animal products, given stark statistical correlation between the two.) But exercise is generally considered to be very healthy, and it may be a decent sign that it’s doing something for you if it also brings down your weight.