Why Swimming Makes You Hungry
Two years ago I attended a very interesting lecture on what science had to say about swimming and your health. The speaker was Dr. Hirofumi Tanaka, Ph.D., the director of the Cardiovascular Aging Research Laboratory at the University of Texas at Austin. According to Dr. Tanaka, a highly respected researcher, there is little to no scientific evidence that swimming is good for your health. Swimmers tend to be “fatter” than other athletes, especially ultra-distance swimmers. Swimming decreases blood pressure, but not as much as cycling or running. Swimmers rank between sedentary people and runners on blood insulin levels, but intervention studies have shown no change. Swimmers’ HDL (high-density lipoprotein - also known as “good cholesterol”) levels are very close to sedentary populations, while runners have very high HDL (Tanaka, 2010). The available research seems to suggest swimming is a lazy sport, but I think otherwise.
There isn’t enough research on swimming, mostly because it’s difficult to take scientific measurements of subjects swimming, or control their absolute workload as can be done on a stationary bike or treadmill. While technology such as heart rate monitors and GPS devices allow the average athlete to assess their relative effort, imagine a scientist running along the length of a pool, pushing a metabolic cart as his subject swims. Though this has been done before, for obvious reasons it’s not common practice. The kind of technology that facilitates this reliable research has a ways to go before we’ll be able to compile the actual evidence.
Swimmers and Body Fat
Why do swimmers tend to have higher adipose (fat) stores than other athletes? Yes, fat is good for floatation and insulation, but the typical age-group triathlete isn’t thinking, “Oh, I better add a thicker layer of fat to increase my swim efficiency,” right? The answer may be buried deep in your brain. One theory is that submerging your body in cold water (68F and below) triggers a hunger response. Your brain doesn’t realize this is a temporary situation, and a cascade of hormones signal tissues to store more fat for insulation, which in turn signals a need for fuel to store. The actual calories utilized during a swim session are comparable to that burnt while cycling or running at the same relative intensity, but due to the immersion in cold water, our appetite may be increased, and therefore our post-swim caloric intake could greatly exceed actual needs.
I’ve often wondered why it is that swimming, though seemingly lower in intensity than cycling and running, leaves me ravenous. No matter how long or short my swim workout, I always leave the pool feeling like I could… eat my young. Luckily, I have no young, so no toddlers have ever been sacrificed in the name of my Ironman training.
So unless you’re in need of a little extra insulation, plan your post-swim nutrition ahead of time, and stick to your plan. Unless you’re training at a moderate-to-high intensity for over 90 minutes or have another workout within 24 hours, your usual balanced meals will replenish any depleted glycogen or fat stores within your muscles before your next session. If you aren’t swimming right before a meal, bring a healthy snack to stave off post-swim hunger. Include some protein and healthy fats for increased satiety and better blood sugar regulation. If you continue to struggle with cravings, try adding a post-swim run to your workout, as running typically suppresses appetite via hormonal responses and an increase in body heat (Russell, Willis, Ravussin, & Larson-Meyer, 2009).
Tanaka, Hirofumi. “Swimming and Cardiovascular Risks”. McCraw Lecture at The University of Texas at Austin. February 26, 2010.
Russell RR, Willis KS, Ravussin E, & Larson-Meyer ED. (2009). Effects of endurance running and dietary fat on cirbulating ghrelin and peptide YY. J Sports Sci Med. 8(4):574-583.