Everyone I know was told as a small child not to swim within an hour of eating. Why is this?
Several people suggested that this is a groundless old wives鈥� tale, although our understanding of physiology suggests otherwise. A few pointed to carbohydrate loading, performed by marathon runners before a race, as evidence that the body copes well with eating and exertion after only a short interval. The question is, how short should that interval be? See Jon Richfield鈥檚 answer below 鈥� Ed
鈥� I swam competitively throughout my school years and still maintain a fitness routine. I frequently consume a large meal and hop back in the pool with no noticeable effects during or after a prolonged casual swim. However, if I were to do a long-distance workout, I would find myself fighting uncomfortable reflux from my recently consumed meal. I鈥檝e found that pickles are the worst. The problem seems to stem from the abdominal twisting that precedes shoulder rotation. Butterfly stroke doesn鈥檛 seem to work 鈥� it feels like doing rapid sit-ups after stuffing yourself. Swimming on a full stomach is undoubtedly less efficient and markedly slower, although I鈥檝e never experienced the cramping that some people report.
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鈥淪wimming on a full stomach is undoubtedly less efficient and markedly slower鈥�
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鈥� The admonition is certainly no longer taken very seriously, as many a postprandial, pandemonic children鈥檚 pool demonstrates every summer. Still, our physiology does adjust radically to meet the challenges of exertion and digestion. Each requires resources to be concentrated on particular functions: we need a lot of blood to process food and transport it from the gut, and that competes with the need for blood to transport oxygen and fuel to muscles.
In nature therefore, a full stomach inclines one towards torpor. Any need for heavy exertion at such times implies an emergency that may justify vomiting to jettison the burden. Snake handlers soon learn that their animals may regurgitate recent meals under stress, and human recruits under military training commonly leave their breakfasts by the roadside during heavy exertion.
One rationalisation for the idea is that because both exertion and digestion demand extra blood supply, swimming after heavy eating may be dangerous for anyone prone to fainting. Anyway, why risk vomiting during a strenuous swim instead of waiting a while? The stomach absorbs very little food, so it is an uncomfortable handicap when full, whereas food in the small gut continuously maintains your stamina while you assimilate it.
Jon Richfield, Somerset West, South Africa