Swimming uses almost all of your major muscle groups. It places a vigorous demand on your heart and lungs.

And when you swim breastroke or backstroke, you’re burning about the same number of calories as a fast walk or a slow jog.

But for some reason, swimming does have a reputation for being less effective than other forms of exercise when it comes to weight loss.

Professor Louise Burke, for example, Head of Nutrition at the Australian Institute of Sport, points out that competitive swimmers typically have body fat levels that are higher than those of runners or cyclists who expend a similar amount of energy when they train.

Many female swimmers have fought well-publicized battles with their body fat levels,” says Burke. “They are generally prescribed ‘land training’ (running or cycling) in addition to their many laps of the pool in the belief that it is a necessary treatment to produce lower skinfold levels.”

The research is a bit of mixed bag, with studies showing that swimming both helps and hinders weight loss.

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One study, published in the American Journal of Sports Medicine, shows that women following a six-month swimming program actually gained weight [1].

Professor Grant Gwinup compared three exercise programs (walking, cycling and swimming). Each program began with up to 10 minutes of daily exercise. The length of each workout was increased by five minutes every week until the women were exercising for 60 minutes daily.

Test subjects following the walking program lost 17 pounds of weight.

Those following the cycling program lost 19 pounds of weight.

However, subjects following the swimming program actually gained 5 pounds.

In other words, subjects who walked or cycled lost weight, while the swimmers put on weight.

But that’s only half the story.

In a similar study, University of Utah researchers found that swimming was just as effective as land-based exercise for weight loss [2].

A group of 38 middle-aged obese women was assigned to one of three groups; walking on land, swimming or walking in water at the shallow end of a pool.

After 13 weeks, all three groups lost, on average, 13 pounds in weight. There were no significant differences between groups, and the swimmers were able to lose just as much weight as those following the land-based walking program.

Why does one study show that swimming is just as effective as land-based exercise when it comes to weight loss, while the other doesn’t?

A closer look at the research reveals why.

The typical temperature range for a swimming pool is between 25.5 and 27.8 degrees Celsius.

In the first study where the swimmers gained weight, they swam in an outdoor pool where the water temperature varied between 23 and 25.5 degrees Celsius. That’s pretty cold.

But in the University of Utah study, the temperature of the water was 27 degrees Celsius, which is much closer to the temperature of most heated swimming pools.

Why does water temperature matter?

Swimming in cold water stimulates your appetite so that you want to eat more.

Many people feel extremely hungry after immersion in cold water [3]. As a result they simply replace all the calories they’ve burned with a large post-exercise meal, completely wiping out any potential weight loss benefits of the swimming.

In a University of Florida study, a group of men exercised for 45 minutes in both neutral (33 degrees Celsius) and cold (20 degrees Celsius) water [4]. They were then allowed to eat as much food as they wanted.

The men burned a similar number of calories in the cold and neutral water conditions, averaging 505 and 517 calories, respectively. However, calorie intake after exercise in the cold water averaged 877 calories, which was 44% more than for the neutral temperature.

The bottom line

When you boil it down, losing weight is all about burning more calories than you eat. Any form of exercise, swimming included, will get the job done.

If you enjoy swimming, then stick with it. It’s far better to be consistent with an exercise program you enjoy than inconsistent with one you hate. But if you’re swimming in cold water, there’s a good chance you’ll come out of the pool with a stomach that feels as empty as a hermit’s address book.

References

1. Gwinup G. (1987). Weight loss without dietary restriction: efficacy of different forms of aerobic exercise. American Journal of Sports Medicine, 15, 275-279

2. Gappmaier E, Lake W, Nelson AG, Fisher AG. (2006). Aerobic exercise in water versus walking on land: effects on indices of fat reduction and weight loss of obese women. Journal of Sports Medicine and Physical Fitness, 46, 564-569

3. Halse RE, Wallman KE, Guelfi KJ. (2011). Postexercise water immersion increases short-term food intake in trained men. Medicine and Science in Sports and Exercise, 43, 632-638

4. White LJ, Dressendorfer RH, Holland E, McCoy SC, Ferguson MA. (2005). Increased caloric intake soon after exercise in cold water. International Journal of Sports Nutrition and Exercise Metabolism, 15, 38-47