Can Exercise Make You GAIN Weight?

The logic is pretty simple: To lose weight, you need to burn more calories than you consume each day by eating less, increasing your general activity levels, and/or working out. But recent research is questioning the idea that burning calories by exercising can help you lose weight—even suggesting that it can lead to fat gain.

Whether you hit up the gym on the regular or are thinking about ramping up your exercise efforts to shed pounds, we delved into this research and previous studies on the subject to see if working out can possibly do more harm than good when you’re trying to lose weight.

How Burning Calories Might Lead to Weight Gain
It sounds so counterintuitive that torching extra calories each day could ever be correlated to fat gain, but that's exactly what a new study published in The Journal of Strength and Conditioning Research is claiming. Previous research examining exercise’s impact on weight loss also suggests that burning calories in the gym isn’t as helpful for weight loss as you would think.

For the study published last month, researchers enlisted 81 women aged 23 to 37 who were not meeting the public health guidelines for physical activity and were not actively trying to lose weight to participate in a 12-week exercise program. Three times a week, the women walked on a treadmill for 30 minutes at a moderate pace so that their heart rate reached 70 percent of their VO2 max—an activity level that is just above the American College of Sports Medicine's minimum recommendation for exercise, according to the study. They were asked not to change anything about their diet during the study. During weeks four, eight, and 12, researchers weighed the participants. At the end of the program, none of the women had lost a significant amount of weight—and 68 percent of them had gained weight. Plus, researchers failed to find any correlation between the women’s baseline measurements (like BMI, body weight, and waist circumference) and their ensuing weight loss (or gain). In other words, the women’s weights before the program were not a good predictor of whether they would lose or gain weight by exercising. 

Granted, this is just one study—so we looked at what other research has to say on the subject. Turns out, a review published in the Journal of Science and Medicine in Sport earlier this year looked at 75 studies about exercise and weight loss and found that the impact of working out on fat and body weight varies from person to person. Many participants in the studies lost much less weight than researchers predicted based on the number of calories they burned during their workouts. For example, one of the studies the review looked at found that participants lost only 30 percent of what they researchers thought they would.

Researchers in both of these studies claim that the mysterious weight gain or lack of weight loss is likely caused by the participants “compensating” for the energy they burned during the exercise program by either eating more or being less active when they weren’t working out.

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The Verdict on Working Out
Even though the newest research shows that the majority of women studied gained weight or didn’t lose anything while burning up to 7,481 calories over 12 weeks, other studies have shown that adding exercise to a weight-loss plan is beneficial.

A 2006 study published in the International Journal of Behavioral Nutrition and Physical Activity, for example, surveyed 4,345 U.S. adults to find out the most successful weight-loss and weight-maintenance strategies—and found that people who worked out more than 30 minutes a day were better at losing weight than those who didn't. Plus, people trying to drop pounds were 48 to 76 percent less likely to be successful if they had an excuse not to exercise, like having no time or being too tired to work out.

A more recent randomized study published in the journal Obesity suggests that exercise can in fact boost weight loss. Researchers studied 439 overweight or obese women between the ages of 50 and 75 over the course of a year. For the study, the women were split into groups: One group only dieted by eating a dietitian's recommendation of calories, the second group just did moderate to vigorous exercise five days a week, the third group used both diet and exercise, and the fourth group—the control group—made no changes. On average, the diet-only group lost about 15 pounds, the exercise group lost about four pounds, and the diet and exercise group lost nearly 20 pounds.

While members of the exercise-only group lost the least amount of weight, it's worth noting that, on average, they also didn't gain weight. Additionally, the diet-and-exercise group lost almost five pounds more than the group that only modified their diet, which shows that hopping on a treadmill probably won't cause you to gain weight.

The newest study casting doubts on the weight-loss benefits of exercise has a few important limitations, says Kristin Kirkpatrick, M.S., R.D., a wellness manager at the Cleveland Clinic Wellness Institute. First, the participants were encouraged not to change their diet so that researchers could see if exercise alone was enough to result in weight loss. But beyond telling the women not to alter their diets, the researchers didn't educate the women on what exactly that meant or ask them to record what they ate each day. That means there's no way to tell how much and what the women ate during the 12 weeks.  "A lot of people think that changing diet simply means adding a food or deleting a food, but even adding a bit more oil or another pat of butter to your meals constitutes a change in diet," she says. That means that the participants might have increased their portion sizes or the amount of calories they were consuming without even knowing it.

Additionally, the study used the minimum guidelines for physical activity—not the recommendation for weight loss, which is 200 to 300 minutes of moderate intensity activity per week, per the Journal of Medicine and Science in Sports and Exercise. So working out for 30 minutes three times a week might have not been enough of a workout to create a substantial calorie deficit, says Kirkpatrick.

Another potential issue with this study is that the people conducting it emphasized that the research was about fitness—not weight loss—to the women when they came in for each supervised exercise session, says Keri Gans, M.S., R.D., author of The Small Change Diet. "Since the women weren't trying to lose weight in the first place and the researchers encouraged them to keep up their current eating habits, they probably weren't keeping a very close eye on how much they were eating," says Gans.

Finally, the researchers did not track how much non-exercise activity the women were doing on their own, says study author Glen Gaesser, professor of exercise and wellness at Arizona State University. Without tracking their daily movements, it was impossible to tell if the women had started moving less or more during the day, which would impact the amount of calories they burned and possibly their weight loss, he says.

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The Benefits of Exercise Beyond Burning Calories
Clearly, the results of this study are a bit questionable due to all of its limitations. But one thing that the study authors want to emphasize is that exercise is a very beneficial tool for your body—even if you're not using it to lose weight. The researchers note in their study that the women were significantly more fit after the 12 weeks than they were beforehand, regardless of whether they lost weight. "It’s far more important health-wise to be fit than to be thin," he says. "The health benefits of exercise are independent of weight loss."

The man has a point; countless studies have shown that there are plenty of reasons to work out that have nothing to do with how you look. Research from the National Cancer Institute indicates that physical activity can lower your risk of breast and endometrial cancer; another study suggests that working out at least two to three times a week can help your body fight bacteria and viruses; and in one study, researchers found that people who lifted weights for 16 weeks increased their hip bone density.

"Don't let this new research make you think that exercise does nothing good," says Gans. "It makes you stronger and is good for your body and mind."

The Upshot If You're Trying to Lose Weight
While heading to the gym to boost your overall health is definitely a great idea, working out to lose weight can be equally beneficial—if you keep a close eye on your diet, says Gaesser.

His study—and others that question the weight-loss benefits of exercise—don't show that working out actually causes weight gain. Instead, most of them point to participants overeating to compensate for the calories they burned working out. Unfortunately, the mechanism behind why some feel the need to eat more and some don't is still unknown, says Gaesser.

With that in mind, you can still use the gym as a tool to help boost your weight loss by tracking how much you're eating, says Kirkpatrick "There's not enough evidence in this new study to say that we shouldn’t get on the treadmill anymore," she says. "This study just shows that to lose weight, you need to be conscious of your diet when working out. You cannot out-train a bad diet."

While the main findings of this study may be somewhat disappointing, the authors note that the weight of the women during week four of the exercise program predicted whether the women would gain or lose weight by the end of the 12-week program. In other words, if they dropped pounds by week four, they would probably continue to lose weight. If they gained, they would probably continue to put on pounds. In turn, the researchers suggest that if you're working out to lose weight, you should weigh yourself after four weeks of consistently exercising to see if you're losing weight or if you're gaining. If you notice the latter, you might be prone to post-workout overeating or need to make more changes to your diet in general, the authors write in in the text of the study. 

The bottom line: There's no evidence that exercise causes weight gain—but it may cause you to subconsciously or consciously take in more calories than you need, which can lead to weight gain (who hasn't felt like they've "earned" a slice of cake after a tough workout?). Don't let that keep you from hitting the gym, though. Instead, keep an eye on what you're eating and use exercise as a complement to a healthy diet.

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