Behavior / Exercise / running

Hungry, Hungry Hippos

Picture taken from a recently submitted question in the New York Times, a reader asked about the health benefits of swimming versus other aerobic exercises.  Reporter Gretchen Reynolds responded that swimming bestows many of the same cardiovascular benefits as activities such as running and walking, and has some additional attributes in that the incidence of orthopedic injuries and over-heating are lower in an aquatic environment. However, one detriment of swimming, she reported, is that swimming may stimulate appetite, making it less appealing for long-term weight maintenance.  I was immediately capitivated because I’ve noticed an unusually strong hunger after swimming, despite the fact that I typically burn fewer calories swimming than running. I was also curious about the answer because as winter encroaches on the Northeast, outdoor exercisers often take to the pool.  Consequently, the question of swimming and appetite seems particularly pertinent to weight maintenance in a cold climate.

Some of the initial evidence that swimming may not be effective for preventing long-term weight gain comes from a study tracking 15,000 adults over 10 years in Washington State.  Interestingly, whereas activities such as running, aerobics and cycling were associated with little to no weight gain over the decade, swimming did not have the same protective effect on weight maintenance. Similarly, in an intervention study in which obese young women were assigned to 60 minutes of daily brisk walking, riding a stationary cycle, or  swimming for 6 months, the walkers and cyclists lost 10-12% of initial body weight, but the women who swam lost no weight. Reductions in body fat were also observed in the walkers and bikers but not swimmers, consistent with observations that adiposity is higher in elite swimmers than runners.  Why?

The answer seems to lie in appetite.  Almost all forms of exercise are associated with appetite suppression during exercise, and after land-based exercise, this appetite suppression persists such that participants do not compensate for caloric expenditure with increased appetite, hunger or caloric intake. This in part explains the role that land-based exercise plays in long-term weight maintenance. Swimming, however, has a slightly different effect on eating.  Researchers in England found that after a bout of swimming laps, study participants reported that “ratings of hunger and prospective food consumption were higher…whilst ratings of fullness were reduced…indicating that swimming stimulated a delayed increase in appetite.” Why the difference between water and land?  Authors of the latter article speculate that temperature may play in important role in appetite control, because prior research found that athletes who cycled on a bike submersed in cold water consumed more food following exercise than after cycling on the same bike submersed in neutral water.  In other words, water temperature may be an important influence on post-exercise calorie consumption. The colder the water, the more you eat afterwards.

So, take-home message? Swimming has many health benefits, but long-term weight maintenance may not be equivalent to that achieved with other forms of moderate intensity land-based exercise. And, if you do swim, seek out a warm pool…with no vending machines nearby.


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