If you were like me as a kid, you probably resented having to wait after eating — seemingly an eternity — before you could go back in the pool. Some parents said to wait an hour; others recommended less time. And what would happen if you disobeyed? Would you really develop a cramp and drown?
If you are now a parent, do you still promote this poolside wisdom? Do you follow it yourself? If so, you might wonder:
- What is the ideal time to wait after eating before returning to the pool?
- Does it matter how much or what you eat?
- Should you wait at all?
The medical literature does not provide ready answers for any of these questions. Specifically, research provides no compelling support for a prolonged waiting period before swimming after eating. On the other hand, no studies clearly refute the recommendation either. Perhaps this lack of published information is because documentation of the specifics of recent meals in cases of drowning or near-drowning is simply unavailable and unrecorded. Alternatively, it may reflect the rarity of the problem, especially in waters that are easy to leave (such as a hotel pool) if problems do develop.
Considering how food is digested, waiting for complete absorption of a meal is clearly unnecessary. After you consume food, enzymes in saliva and the stomach begin the digestive process right away. About half of the consumed food remains in the stomach for two hours; it takes about four hours for the stomach to completely empty. Food spends another two hours in the small intestine and 14 hours in the large intestine. Moreover, what you eat makes a difference in terms of digestion. Simple carbohydrates (such as the sugar in an apple or a carbonated beverage) may be digested more quickly than a fatty meal (for example, a cheeseburger).
After a meal, there is an increased flow of blood to the stomach and intestines to absorb nutrients. This increased blood flow leaves less blood available to deliver oxygen and to remove waste products from exercising muscles, including those muscles involved with breathing. Trying to exercise after eating thus sets up competition for blood flow between the digestive organs and the muscles. It is thought that some abdominal or muscle cramps (including what is often called a stitch) might be caused by an inability to meet the increased demands of both areas.
Is this situation dangerous? If cramping occurs, will it paralyze or otherwise incapacitate a person so suddenly that he or she could drown if in the water? It is possible. However, if drownings or near-drownings have ever occurred because a person did not wait long enough after eating, these events are rare. More important risk factors for drowning include not knowing how to swim, alcohol use, a lack of safety gear on boats and a lack of protective fencing and covers for pools.
The notion that swimming soon after eating is dangerous may be a medical myth based on commonsense, intuition and the oral tradition that passes "wisdom" down from generation to generation. Strenuous exercise after a large meal is often uncomfortable, so taking some time to digest (more time for larger meals) makes sense, but failing to do so is probably not the enormous danger about which we are often warned.
Age-old wisdom may not always be based on sound scientific reasoning, but listening to signals from your body does makes sense — if you experience pain, cramping or severe fatigue when swimming, perhaps you did go back in the pool too soon.
Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.