High-protein diets used as a means of losing weight could be damaging to the kidneys, according to a warning from the American Kidney Fund (AKF).
The diets place such a significant strain on the kidneys that even conditioned athletes can become dehydrated, the AKF said, citing researchers at the University of Connecticut.
Paul W. Crawford, the AKF's chairman of medical affairs, said: "We have long suspected that high-protein weight loss diets could have a negative impact on the kidneys, and now we have research to support our suspicions. Dehydration forces the kidneys to work harder to clean toxins from the blood. Kidneys not only filter the blood, but they also help regulate blood pressure and the number of red blood cells."
According to the AKF, the Connecticut researchers studied five fit endurance runners who consumed a low, then a medium, and finally a high-protein diet. During the high-protein phase, the runners consumed about 30 per cent of their total calories from foods such as eggs, steak, and so-called 'power bars'.
Blood tests showed that increasing the protein intake led to a progression toward dehydration, and that a greater strain was placed on the kidneys due to the excessive amount of protein.
"Increased protein intake leads to a build-up of nitrogen in the blood. The nitrogen ends up at the kidney in the form of urea, where it needs to be cleaned from the blood and got rid of in the urine," explained Crawford. "The resulting increase in urination can cause dehydration, further straining the kidneys," he added.
In otherwise healthy individuals, a protein intake of no more than two grams of protein per kilogram of body weight was recommended by the researchers in order to avoid negative long-term effects.
Crawford also discussed the risk that body builders take in eating high-protein diets while building muscle. "Bodybuilders could be predisposing themselves to chronic kidney disease because hyperfilteration (the strain on the kidneys) can produce scarring in the kidneys, reducing kidney function."
He continued: "Chronic kidney disease is not to be taken lightly, and there is no cure for kidney failure. The only treatments are kidney dialysis and kidney transplantation. This research shows that even in healthy athletes, kidney function was impacted and that ought to send a message to anyone who is on a high-protein weight loss diet."