I wasn’t going to post this week because I have some other things I need to attend to, but then this bit of empty clickbait popped up, a Vox article claiming “The science is in: exercise won’t help you lose much weight”. This is yet another example of people making money by misleading the public on the subject of weight loss.
To say that exercise won’t help you lose much weight is like saying that guns don’t kill people, people kill people: there’s just enough fact (as opposed to truth) to dupe the public into buying a falsehood. So let’s look—very quickly–at some of the assumptions this article makes and why they are incorrect, and ultimately destructive.
First and most important: Why are we talking about weight at all? Without context–meaning a broader set of data points—it is a meaningless abstraction. If you tell me you’re a woman who weighs 150 lbs., that tells me nothing about your health or how fat or skinny you are. What matters is your body composition: the ratio of fat to lean muscle you have. But even if I know that you’re 150 lbs. and relatively tall and skinny, this tells me nothing about your general health outlook, since you can still be skinny-fat, meaning you have too high a fat-to-muscle ratio. So ditch your scale and start focusing on your body composition: losing fat and gaining muscle (which may or may not change your weight).
Second: this article is stuck back in the antediluvian era of calorie burning as weight loss, an era that also, like this article, equated exercise exclusively with aerobic efforts. Both assumptions are extremely problematic.
But let’s grant the author her assumptions for the moment (and yes, she is relying on scientific studies, but they too can be quite misleading). She writes: “Exercise accounts for a small portion of daily calorie burn.” We are not machines: we do not burn calories, we metabolize food—and thus which foods those calories come from will significantly affect how we store the energy in them. And how we exercise will also affect how we metabolize our food. I’ll come back to this toward the end of this post.
“It’s hard to create a significant calorie deficit through exercise”: The operative word here is hard. Yes, folks, exercise, properly done, is not easy. She gives the example of a 200 lbs. man running 60 minutes 4 days per week at “medium intensity.” I don’t know what she means by medium intensity: when I run for 60 minutes, I burn between 800 and 1000 calories, which is plenty to put me in caloric deficit, given her model of eating 3500 calories per day. But her chart, which comes from NIH, claims that this hypothetical man will only lose about 5lbs over 30 days, so he’s losing about .16 lbs. per day. That sounds like extremely low-intensity running to me. To put it into perspective, when I work out, I’m “burning” far fewer calories than 800—I’m strength training, not running—but I lose a consistent 1.3 lbs. per day, that’s nearly a ten-fold difference. If he’s eating right and running fairly hard, he ought to lose at least 12lbs., per month.
So the author is assuming very low intensity exercise, or barely exercising at all, more like walking for 60 minutes. But really what she’s assuming is her next point: “Exercise can undermine weight loss in other, subtle ways”. Her tacit arguent is that many people overeat or eat the wrong things after exercise. So, if she weren’t just polluting the internet with clickbait, she’d have titled her piece “Exercise, without a healthful diet, won’t help you lose much weight.” She’d be more accurate, but then nobody would read the piece, and I wouldn’t have to blog about it.
But let’s go back to this notion of “exercise” in the first place, for as I said, how you exercise will also affect your body composition and calorie use. She only talks about aerobic exercise, which is again quite misleading because aerobic exercise might use up a bunch of calories, but it does nothing to help you gain muscle. And muscle is extremely important for carbohydrate metabolism. Muscle stores glucose, meaning it takes those pesky calories you’ve eaten and stores them as more muscle, rather than fat. In addition, muscle increases insulin sensitivity, which in turn affects how you store the energy you consume.
Muscle also is also active tissue, meaning it “burns” calories, whereas fat is inert, it uses no calories. Now, before you go and tell me that the amount of calories muscle uses is actually rather low, I have two retorts. One: how much muscle are we talking about? And two: all those estimates of how many calories resting muscle uses completely ignore the fact that to gain muscle at all, you need to constantly break it down and rebuild it: in other words, it is rarely at rest; most of the time it will be very actively rebuilding broken-down tissue (and if you have a diet with high micronutrient density, the more calories you consume—to a point—the more muscle repair will occur).
In conclusion: if you want to lean out instead of just losing weight, the answer is very simple: Do strength work as well as aerobic exercise and eat real foods, not too much (to quote Michael Pollen).