Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.
Intro: Spoiler alert: swimming, a popular form of exercise that’s easy on the joints, turns out to not be good for weight loss. You’re working hard, burning calories, so why don’t the inches and pounds come off? Watch the video to find out.
Swimming and aquatic exercise in general are popular alternatives to land-based activities such as walking or biking. The buoyancy helps take some of the weight-bearing stress off of joints, but swimming appears to be less effective for weight loss. Obese women were randomized into an hour a day of walking, cycling, or swimming. Six months later, the walkers lost an average of 17 pounds, the cyclists lost an average of 19 pounds, and the swimmers didn’t lose an ounce (in fact, they actually gained 5 pounds). Gauging skin folds to estimate body fat, the measurements slimmed more than 40 percent in the walking and cycling groups, but there was no change at all in the swimming group. What’s going on? And check this out. The more the women walked, the more they lost weight. The more the women biked, the more they lost weight. But the more laps they did didn’t seem to matter. Even an hour a day. No weight loss. What is going on?
Well, it turns out that some exercise boosts appetite more than others. While land-based exercise does not stimulate a compensatory increase in appetite and calorie, the same cannot be said of water-based exercise. In contrast to walking, in contrast to running, and in contrast to cycling, swimming can significantly heighten hunger within hours. This may explain why swimmers tend to have more body fat than runners of equal caliber, even though they may be actually expending more calories during training. If anything, you’d think swimming might lead to even greater weight loss since you’re losing heat to the water. But swimming didn’t seem to work at all. The cold, it turns out, may actually be the culprit.
If you exercise in warm water (about 90º F) it doesn’t boost your appetite more than exercising on land. After the same workout in cool water (about 70ª F), people can end up eating more than twice as much at a meal an hour later. Maybe they’re just burning off extra calories to stay warm? No, even at the same number of calories expended, people eat hundreds of calories more after exercising in cold water. Offered a buffet after burning off about 500 calories in cool water, people eat nearly 900 calories, hundreds more than after exercising in warm water or just staying dry. So, they ended up taking in about twice as many calories as they exercised off. No wonder swimming doesn’t appear useful for weight loss.
Would the same thing happen under different temperatures on land? A team of British researchers sought to find out, randomizing people to briskly walk for 45 minutes on a treadmill in the cold (about 46º F) or at closer to room temperature (about 68º F). Participants were then presented with a buffet meal in which their eating was covertly recorded. And calorie intake was significantly greater after exercising in the cold. Though walking is often prescribed for overweight individuals, the researchers conclude, “if walking was to take place in a cold environment, such as in winter, then this may stimulate food intake.” In the warmer months, though, obesity researchers suggest exercising outdoors may be preferable to an air-conditioned gym.
All studies to date on the effects of hot and cold environments have found that exercising in cool water or under cool conditions on land led to an increase in post-workout calorie intake. What about a quick dip in the pool after you exercise? Australian researchers found that immersion in water for 15 minutes—cool or warm—after a running session resulted in increased calorie intake. What is it about getting wet that whets your appetite? Maybe they got a chill after getting out before they could change into dry clothes? This suggests that though a cool shower after a workout may be invigorating, it might be better to stick to hot.
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