Dehydration: Why Does a Higher Protein Diet Necessitate More Water?

High-protein, low-carbohydrate diets are popular for weight loss. Bodybuilders and others who want a lean, muscular physique often use a high-protein, low-carbohydrate diet as well.

Does this put them at risk of dehydration? In 2002, researchers put that question to the test by designing a small study to see how a high-protein diet affected trained endurance athletes.

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


Thirst isn’t always a reliable early indicator of the body’s need for water. Many people, particularly older adults, don’t feel thirsty until they’re already dehydrated. That’s why it’s important to increase water intake during hot weather or when you’re ill.

The signs and symptoms of dehydration also may differ by age.

Infant or young child

  • Dry mouth and tongue
  • No tears when crying
  • No wet diapers for three hours
  • Sunken eyes, cheeks
  • Sunken soft spot on top of skull
  • Listlessness or irritability


  • Extreme thirst
  • Less frequent urination
  • Dark-colored urine
  • Fatigue
  • Dizziness
  • Confusion

When to see a doctor

Call your family doctor if you or a loved one:

  • Has had diarrhea for 24 hours or more
  • Is irritable or disoriented and much sleepier or less active than usual
  • Can’t keep down fluids
  • Has bloody or black stool


Sometimes dehydration occurs for simple reasons: You don’t drink enough because you’re sick or busy, or because you lack access to safe drinking water when you’re traveling, hiking, or camping.

Other dehydration causes include:

  • Vomiting and diarrhoea. Severe, acute diarrhoea, or diarrhoea that appears abruptly and violently, can result in a massive loss of water and electrolytes in a short period of time. You lose much more fluids and minerals if you have both vomiting and diarrhoea.
  • Fever. The higher your fever, the more likely you are to become dehydrated. If you have a fever along with diarrhoea and vomiting, the situation becomes more worse.
  • Sweating excessively. Sweating causes you to lose water. You can become dehydrated if you engage in vigorous activity and do not refill fluids as you go. The amount of perspiration you produce and the amount of fluid you lose increase in hot, humid weather.
  • Increased urination. This may be due to undiagnosed or uncontrolled diabetes. Certain medications, such as diuretics and some blood pressure medications, also can lead to dehydration, generally because they cause you to urinate more.

High Protein Diet Study

William Martin, a graduate student at the University of Connecticut, did the research. He presented his findings at the Experimental Biology symposium in 2002. Five university student-athletes who were well-trained runners served as test subjects.

These endurance athletes were put on a variety of different protein-based diets. Their diets were meticulously monitored to verify that they were following the study’s guidelines.

For the first four weeks, each participant followed a low-protein diet (e.g. a 150-pound person would have 68 grams of protein daily). They were on a moderate-protein diet for another four weeks (e.g. 123 grams daily).

In the last four weeks, they had a high protein diet (e.g. 246 grams daily). This last diet matched what many popular high protein diet programs recommend, with 30% 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 are given had twice and four times the RDA respectively.

Protein, Hydration, and Thirst

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.


To prevent dehydration, drink plenty of fluids and eat foods high in water such as fruits and vegetables. Letting thirst be your guide is an adequate daily guideline for most healthy people.

People may need to take in more fluids if they are experiencing conditions such as:

  • Diarrhea or vomiting. Start offering extra water or an oral rehydration solution to your child if he or she is vomiting or has diarrhoea at the first sign of illness. Don’t wait until you’re dehydrated.
  • Exercising is difficult. It’s advisable to begin hydrating the day before a heavy workout. It’s a positive sign that you’re hydrated if you have a lot of clear, dilute pee. Replace fluids at regular intervals throughout the exercise, and continue to drink water or other fluids after you’ve completed.
  • Weather might be hot or chilly. In hot or humid conditions, you should drink more water to help lower your body temperature and replace what you lose via sweating. In cold weather, you may need more water to prevent moisture loss from dry air, especially at higher altitudes.
  • Illness. Older adults most commonly become dehydrated during minor illnesses — such as influenza, bronchitis or bladder infections. Make sure to drink extra fluids when you’re not feeling well.

Why Drink More Water

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 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 2% to 3% decrease in body water has been found to negatively affect athletic performance and cardiovascular function. Whether you are exercising or not, it is important to make sure you are drinking enough to prevent dehydration.

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