I eat more when i exercise? how to lose weight, but gain muscle
Won’t exercise make me eat more and gain weight?
In 2009, Time magazine ran a cover story called “Why Exercise Won’t Make You Thin,” in which journalist John Cloud described his unsuccessful attempts to lose weight through exercise. Cloud’s central theme, supported by his own fondness for post-workout blueberry bars and a rather selective sampling of research, was that exercise actually makes you hungrier. As a result, he warned, “fiery spurts of vigorous exercise could lead to weight gain.” The twisted logic that led to this conclusion was widely condemned by obesity researchers—but it did raise an important question. After all, it’s undeniably true that many people exercise diligently without losing weight. And exercise does make you hungrier.
Some simple math illustrates what you’re up against. Let’s say you go out and bike six miles in about half an hour, then chug a typical recovery shake. You’ve burned about 280 calories and immediately downed 270 calories—so you haven’t accomplished much. The number of calories burned through casual exercise almost always corresponds to a surprisingly small chunk of food. That means dropping weight is not an easy process. But there’s no evidence to suggest that exercise actually causes you to gain weight.
It’s true that increasing your physical activity levels can make you feel hungrier, but the same is true of eating less. Your body will respond to any change that results in you taking in fewer calories than you burn with a series of physiological and behavioral tactics that conspire to keep you at your current weight. That’s why almost none of the weight-loss interventions that have been tested in clinical trials achieve losses that the majority of participants sustain beyond a few years. It’s not just exercising to lose weight that’s hard—it’s losing weight by any means.
Of course, there’s no debate that elite athletes drop pounds and keep them off through exercise. In fact, for long-distance runners, swimmers, and Tour de France cyclists, eating enough to meet their caloric needs is a constant challenge. So it’s clear that exercise really can help you lose weight—the only question is how much. A recent Harvard University study offers some clues. Researchers followed 34,000 middle-aged women for 13 years, monitoring their diet, exercise, and weight and reporting the results in the Journal of the American Medical Association in 2010. Just 13 percent of these women (who were eating “typical” American diets with no intervention) managed to avoid significant weight gain throughout the study, and these women averaged a full hour of moderate exercise every day. Anything less was unsuccessful. That’s a lot of exercise—unless you compare it to the daily lives of our ancestors who didn’t spend most of the day sitting at desks or in cars.
In a sense, Cloud’s article was a wake-up call to anyone who thought that heading to the gym for half an hour a few times a week would, on its own, transform their bodies. You also have to pay attention to what you eat, both immediately after your workout and throughout the rest of the day. But the article’s most serious sin was underplaying the other benefits of exercise, from cardiovascular health to stress relief, that accumulate even if your weight isn’t changing. Exercise—and particularly “fiery spurts of vigorous exercise”—is the most powerful force for good health that we know of. And it won’t make you gain weight.
Can I lose weight while gaining (or maintaining) muscle?
In a perfect world, you’d be able to exercise and eat in a way to make your muscles grow bigger while your fat stores shrink. This is possible in some cases—but for most of us, a more realistic goal is to lose weight by dropping fat without losing useful muscle mass. This is particularly important for athletes who compete in weight classes, like wrestlers, who don’t want to weaken themselves while trying to “make weight.” Researchers have been studying the problem for the past few years, and they now believe that one of the keys is making sure you’re getting enough protein.
Protein gets a lot of hype for its weight-loss potential. For one thing, foods containing protein make you feel more full, so you’re likely to consume fewer calories overall. Some research suggests that protein helps maintain levels of a hormone called triiodothyronin, which counteracts the tendency of your resting metabolism to slow down when you lose weight. Protein is also a relatively inefficient fuel: your body has to burn 25 percent of the available energy just to convert it to a usable form. These factors all sound great, but it’s not yet clear that they make any appreciable difference in your attempt to lose weight and maintain muscle. There’s stronger evidence for the role of leucine, one of the essential amino acids provided by dietary protein, in stimulating your body to create more muscle protein.
In practice, several studies have found that higher protein diets help overweight or obese subjects lose more fat while retaining more muscle compared with diets with less protein. But it’s important to clarify what “higher protein” means in this context. For example, the diets in a 2005 study at the University of Illinois contained either 0.8 grams of protein per kilogram of body weight (g/kg/day) or 1.6 g/kg/day. In this case, the “high-protein” diet actually corresponded to the amount of protein in a “typical” North American diet, which is about 1.6 g/kg/day—equivalent to about three-quarters of a pound of chicken breast for someone who weighs 150 pounds. So the message isn’t to eat more protein; it’s just to avoid slashing your protein intake if you’re cutting calories.
Athletes in training face somewhat different challenges. They have less fat to start with, which means any weight loss is more likely to come from muscle. But the same basic pattern holds true, according to a 2010 study at the University of Birmingham. Researchers found that a diet containing 2.3 g/kg/day of protein (35 percent of calories) helped athletes maintain their muscle mass far better than a diet containing 1.0 g/kg/day (15 percent of calories). They lost roughly the same amount of fat on both diets.
Another key factor that athletes need to consider before ramping up their protein intake is that carbohydrates are the most important fuel for extended bouts of exercise. A study in New Zealand found that even a single week on a high-protein diet with 3.3 g/kg/day of protein was enough to slow endurance cyclists by 20 percent on a two-hour time trial, compared with a high-carbohydrate diet with just 1.3 g/kg/day of protein. This suggests that you shouldn’t emphasize protein at the expense of carbohydrate, which leaves fat as the only remaining candidate for reduction.
Ultimately, the message is balance. Too little protein, and you’ll lose muscle mass (assuming you’re also eating fewer calories overall than you’re burning). Too much protein at the expense of carbohydrates, and you’ll suffer at the gym. As long as you’re realistic about your weight-loss goals, aiming for no more than a pound a week, you can get there without dramatic deviations from a normal, balanced diet—one that doesn’t go heavy on the protein.