High Protein Diets Cause Dehydration, Even in Trained Athletes

Why you need to drink more water with a high protein diet

A plate of protein sources.
A plate of protein sources. Adam Gault/Getty Images

High protein, low carbohydrate diets are popular for weight loss, but could they cause dehydration? A small study put that question to the test. Beyond weight loss, bodybuilders and others who want a lean, muscular physique often use a high protein, low carbohydrate diet. Does this put them at risk of dehydration?

On the opposite side, endurance athletes such as marathon runners and cyclists are usually told to eat a balanced diet that includes carbohydrates to maintain their energy stores.

Their training often adapts them to dehydration more than the average person, according to the study researchers. They designed a study to see how a high protein diet affected trained endurance athletes.

"We found that certain hydration indices tended to be influenced as the amount of protein in their diets increased," said Nancy Rodriguez, an associate professor in nutritional sciences who oversaw the study, in a press release.

High Protein Diet Study

The study was conducted at the University of Connecticut by graduate student William Martin. He presented his research to the Experimental Biology 2002 meeting. The test subjects were five student athletes from the university who were well-trained runners. These endurance athletes were put on diets that varied in the amount of protein, based on a 150-pound person. Their diet was closely monitored to ensure they were adhering to the study protocol.

For four weeks, each first had a low protein diet of 68 grams daily. For another period of four weeks they had 123 grams of protein for a moderate protein diet. In the last four weeks, they had a high protein diet with 246 grams of protein daily. This last diet matched what many popular high protein diet programs recommend, with 30 percent of the calories coming from protein.

These regimens span the range of what is recommended. At the time of the study, the USDA recommended daily allowance for protein was 70 grams for a 150-pound person. That matches the low protein diet given to the test subjects. The moderate and high protein diets given were twice and three times the RDA.

Protein Up, Hydration Down, But No Thirstier

The study subjects were tested for their blood urea nitrogen (BUN), urine concentration and other lab values every two weeks during the study. The BUN test is one performed routinely as an indicator of kidney function. It measures the breakdown products of protein that are cleared by the kidneys. Alarmingly, the BUN reached the abnormal range when the student athletes ate the high protein diet. Their urine was also more concentrated, which is a sign of dehydration. Their values returned to normal when they went back to their usual diet. They didn't feel thirstier when on the high protein diet, and so they might not have been drinking enough water to meet the needs of their kidneys to dispose of the waste products of digesting protein.

Drink More Water on a High Protein Diet

"Based on our findings, we believe that it is important for athletes and non-athletes alike to increase fluid intake when consuming a high protein diet, whether they feel thirsty or not because our study subjects said they did not feel a difference in thirst from one diet to the next," said Rodriguez in a press release.

The American College of Sports Medicine's position stand on nutrition and athletic performance recommends staying well-hydrated before, during and after exercise to balance fluid losses. Sports drinks with carbohydrates and electrolytes can decrease the risk of dehydration and hyponatremia.

As little as a two to three percent decrease in body water has been found to negatively affect performance and cardiovascular function. Whether you are exercising or not, it is important to make sure you are drinking enough to prevent dehydration.


High Protein Diets Can Lead to Dehydration. Apr. 22, 2002, University of Connecticut.

High protein diets cause dehydration, even in trained athletes. 22 Apr. 2002. Federation of American Societies for Experimental Biology. Meeting, Experimental Biology 2002.

American Dietetic Association; Dietitians of Canada; American College of Sports Medicine, Rodriguez NR, Di Marco NM, Langley S. "American College of Sports Medicine position stand. Nutrition and athletic performance." Med Sci Sports Exerc. 2009 Mar;41(3):709-31. doi: 10.1249/MSS.0b013e31890eb86.

Continue Reading