(19 of 20)
-- W --
WAIST Your belt size may have more to do with your health than your vanity. New research showed that a large waist is associated with insulin resistance and metabolic syndrome--a precursor condition to cardiovascular disease and diabetes--in children and adults. A study of 27,270 men found that thick-in-the-middle guys--with 40-in.-to-62-in. waists--are 12 times as likely to develop Type 2 diabetes as men measuring 29 in. to 34 in. around. Studies also supported the contention of many experts that the waist-to-hip ratio is a more accurate measure of obesity and a better predictor of heart-attack risk than the widely used body mass index.
TIM DE WAELE / CORBIS
WATER Staying hydrated while exercising is important, but drinking too much water can be as dangerous as not drinking enough. Research showed that hydrating too much over the long haul--during a marathon, say, or a long-distance bike ride--dilutes the blood's salt content and can lead to hyponatremia. The body's cells, including brain cells, absorb the excess fluid and swell, and growing pressure in the skull can cause permanent damage or death. Hyponatremia is surprisingly common; in a study of 488 runners of the 2002 Boston Marathon, 13% were over-hydrated. Many of the symptoms of hyponatremia--nausea, dizziness, confusion, lethargy--mimic those of dehydration. The authors of the Boston study offered a handy way to test yourself: if you weigh more after exercising than before, you're drinking too much.