Copyright 2007 www.DrMirkin.com.
Used by permission.

Gabe Mirkin, M.D.

During World War II, Dr. James Gamble of Harvard Medical School showed that you have to take huge amounts of salt when you exercise for several hours, particularly in hot weather. Nobody has improved on his research in the last 60 years.

After Gamble published his studies, people who work in the heat were given salt tablets, which is such a concentrated form of salt that it can cause nausea, so some doctors stopped prescribing salt tablets. In the 1960s, doctors became concerned that too much salt can cause high blood pressure, so many doctors stopped recommending heavy salting of food, causing many people to die of heat stroke and dehydration during hot weather work and exercise.

A low-salt diet does not lower high blood pressure in most people with high blood pressure. A high-salt diet causes high blood pressure usually only in people with high blood insulin levels. Heavily salting food and drinking salty drinks when you exercise for more than 2 hours in the heat should not raise blood pressure anyway. If you don't take salt and fluids during extended exercise in hot weather, you will tire earlier and increase your risk for heat stroke, dehydration and cramps.

Schmidt W et al. Plasma-electrolytes in natives to hypoxia after marathon races at different altitudes. Medicine and Science in Sport and Exercise. 1999 (October);31(10):1406-13.




Copyright 2007 www.DrMirkin.com.
Used by permission.

Gabe Mirkin, M.D.

If you watch a major bicycle race on TV, you have to be impressed by how the riders can eat enough to sustain them through races that require more than five hours of near maximum effort. If they do not get enough food during their ride, they can fall off their bikes, lie on the ground unconscious and start to shake all over in a in a massive convulsion. This is called bonking: passing out from low blood sugar.

Your brain gets almost all of its fuel from sugar in your bloodstream. When your blood sugar level drops, your brain cannot get enough fuel to function properly, you feel tired and confused and can pass out. There is only enough sugar in your bloodstream to last three minutes. To keep your blood sugar level from dropping, your liver must constantly release sugar from its cells into your bloodstream, but there is only enough sugar in your liver to last 12 hours at rest. During intense exercise, your muscles draw sugar from your bloodstream at a rapid rate. Your liver can run out of its stored sugar and your blood sugar level can drop, and you bonk.

Bonking is common in bicycle races if a rider does not eat frequently, but is rare in long distance running races. When you run, your leg muscles are damaged from the constant pounding on the roads and you must slow down. However, you pedal in a smooth rotary motion which does not damage your muscles, so you can continue to pedal at a rapid cadence for many hours.

To prevent your blood sugar from dropping too low during intense exercise lasting more than two hours, eat at least every 15 minutes. It doesn't matter what you eat: salted peanuts, a peanut butter and jelly sandwich, chicken, an apple, a banana or anything else. Almost all fit people can take small amounts of food frequently during exercise without developing stomach cramps.


Also read this article from Runner's World magazine on bonking.



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