Some ideas in bodybuilding are accepted as fact and rarely questioned. One example is the frequent warning that you can’t digest large amounts of protein in one meal. Somewhere along the line the figure of a maximum of 30 grams per meal was established for everyone. Although I’ve studied nutrition for 40 years, I’ve yet to see a study confirming that amount of protein; however, I have seen studies showing that protein uptake relates to need, as is true with other nutrients. That means if you require more protein, your body will absorb more.
Another classic example of nutritional dogma is the notion that you must drink at least eight eight-ounce glasses of water every day. People who espouse that, including many nutritionists, also warn that coffee and alcoholic beverages, though fluids, don’t count. They say that caffeine and alcohol have a diuretic action.
But are such assertions based on fact? In a provocative review that will be published in the American Journal of Physiology, Heinz Valtin, of the department of physiology at Dartmouth Medical School, examines the origins of the 8×8 water requirement. He notes that the emphasis on water intake is so widespread that it’s common to see people carrying water bottles around with them everywhere.
Valtin traces the water admonition to advisories from the Food and Nutrition Board of the National Research Council in 1945. Another possible source: a casual statement in a 1974 book by Frederick Stare, who headed the nutrition department at Harvard University.
Even so, Valtin could find nothing in any scientific publication proving the need for 8×8. Nor does any research support the idea that caffeine and smaller amounts of alcohol don’t count toward daily fluid intake. Rather, existing data show that the body is capable of accurately monitoring adequate fluid levels.
What about the much-touted benefits of a high water intake? Many such claims make sense initially, based on the composition of the human body. Water represents 50 to 70 percent of bodyweight; muscle alone is nearly 80 percent water. Water lost through normal physiological mechanisms every day should be replaced; hence the 8×8 rule.
Some research connects health benefits to increased water intake. One study shows that you can reduce the risk of bladder cancer by 7 percent for each additional eight-ounce glass of water you drink, though that finding applies only to men. Other studies show that increased fluid intake helps prevent the onset of colorectal cancer, presumably by easing the passage of food through the intestines. A few studies show that increased water intake may even help prevent cardiovascular disease, a function of decreased blood viscosity, or thickness, which helps prevent blood-clot formation. Sufficient water intake may help relieve or prevent bladder infections and kidney stones.
Research suggests that increasing water intake helps people lose fat by lessening appetite and flushing fat-based ‘poisons’ out of the body. Insufficient water and fiber will cause constipation in most people. According to Valtin, the long-accepted view that more water may help protect kidney function isn’t necessarily true, either, though it does help those with existing kidney disease.
What about the flip side, the dangers of too much water? Water intoxication leads to a loss of vital electrolytes in the brain and can result in anything from convulsions to death. That’s happened to teens at raves who drank copious amounts of water after taking the drug Ecstasy, which induces intense thirst but also promotes secretion of vasopressin, an antidiuretic hormone.
Valtin notes that increased water intake may expose you to environmental pollutants in the water. Drinking too much water will also lead to increased urination, which could prove problematic under some circumstances.
Among other myths that Valtin discusses is the idea that once you experience thirst, you’re already dehydrated. But he points out that the body has an exquisite system to monitor the increased concentration of solids in the blood under low-fluid conditions. Thirst begins when the blood concentration level rises by 2 percent, while true dehydration begins when the level is at 5 percent.
Another misconception is that dark urine represents dehydration. Valtin cites the body’s ability to monitor the osmolarity, or level of solids in the blood, and make adjustments accordingly. Taking in more protein and other nutrients, such as riboflavin, or vitamin B2, can also darken the urine color, but it’s a harmless effect.
Valtin observes that while most healthy people are likely getting enough water, adjustments in fluid intake are necessary in some circumstances: certain diseases, strenuous physical activity, long airplane flights, hot climates. And you should be aware not only that caffeine-containing drinks and small amounts of alcohol-based drinks do count toward daily fluid intake but also that food counts too. Fruits and vegetables are mostly water.