By E. J. Mundell

NEW ORLEANS, Apr 22 (Reuters Health) - High-protein diets place such a strain on the kidneys that even very fit athletes can become dehydrated, according to researchers.

"Personally, I would not recommend a protein intake of over 2 grams of protein per kilogram of weight per day, as it may have negative long-term effects," said researcher William Forrest Martin, a graduate student at the University of Connecticut in Storrs. He presented the findings here Monday at the Experimental Biology 2002 conference. (Note - 1 kg = 2.2 lbs ... Doreen)

High-protein diets have surged in popularity in recent years for their purported potential for quick weight loss. Most of these plans promise prompt results if devotees fill up on steak, bacon, fried eggs and other high-protein foods, while cutting back on carbohydrates such as potatoes, pasta, vegetables and fruit.

But the diets have their critics. For example, the American Heart Association recently issued a report that found that there was "no scientific evidence" that the diets actually worked to keep pounds off over the long term, and they may trigger unwanted side effects such as fatigue or dizziness.

In their study, Martin and his colleagues sought to determine the effects of such diets on hydration--the body's ability to distribute and retain a healthy amount of water. They had five very fit endurance runners consume low-, medium- and high-protein diets over three successive 4-week periods. During the high-protein diet phase, participants consumed about 30% of their total calories from foods such as eggs, steak and "power bars."

Blood tests conducted on the athletes 3 weeks into the diets revealed "that increasing protein intake led to a progression toward hypo- (low) hydration, and that a greater strain was placed upon the kidney due to the excessive levels of protein intake," according to Martin.

Speaking with Reuters Health, he explained that increased protein intake leads to an excess build-up of nitrogen in the blood. "In the end, the nitrogen ends up at the kidney in the form of urea where it needs to be filtered out and excreted in the urine."

The excessive urination triggered by high protein intake can easily lead to a hypohydrated state, even in the absence of symptoms. In fact, all of the runners in the study said they felt no more thirsty while on the high-protein diet compared with other regimens--even though their levels of hydration had fallen to below healthy levels.

Based on the findings, Martin advised active individuals to avoid getting a large percentage of their calories from meat, eggs and other protein-rich foods. But "if one does embark on a diet greater than about 1.8 grams per kilogram of body weight per day, I would suggest they increase their daily fluid intake to protect against dehydration," he said.

According to the American Dietetic Association, the average adult should consume between 8 to 12 cups of water per day.

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