High-protein diet is not good for all organs in our body
High-protein diet is bad for kidney health.
Doctors, nutritionists and other healthcare professionals often comment on the benefits of a high-protein diet, such as rapid weight loss, greater calorie burn, reduced appetite, obesity prevention, and diabetes treatment.
If we went back in time, we would see that the human diet was a diet with less than 2,500 calories per day (on average), with proteins contributing to less than 10–15% of the total energy. Protein intake for our ancestors was less than 1 gram per kilogram of body weight per day, and most likely 0.6-0.8 grams per kg of weight per day. Carbohydrates and fat made up the remaining 85% of the calories in each person’s daily diet. But we do not need to go that far back in time, since these numbers were true for times as recent as the World War II.
It is worth noting that until the recent 1960s, obesity was not a problem and type 2 diabetes was very rare.
The current trend is to eat more meat and animal foods, following diets with higher amounts of proteins. These diets often prescribe daily protein intakes of 20–25%, and sometimes even more, of total calories per kilogram of body weight per day — effectively twice the amounts mentioned before.
What are the consequences of these diets?
High-proteing diets make our kidneys work harder, and cause what is known as glomerular hyperfiltration — that is, the increase in glomerular filtration rate (GFR). To fully understand what this means, we need a little sidetrack.
Aging is a phenomenon almost universal in biology, only partially controlled by genetic endowment. Individuals and their organs age at different rates. The kidneys manifest the process of aging through the constant loss of nephrons and a corresponding decrease in GFR from age 30 — which can be reasonably qualified as decreased kidney function. Starting at age 40, humans experience a gradual loss of kidney function, a small annual loss of about 1% of the function of these organs. But this is no cause for concern. The “modest” reduction in GFR observed in the elderly — which is 45–59 ml/min/1.73 m² and are values that can be roughly equated to about half of kidney function — does not seem to have much effect on life expectancy or produce adverse effects (as long as no other kidney changes are detected, especially in urine tests). This is to say older kidneys are not “sick” kidneys.
For those with normal kidney function, high-protein diets may not be harmful. Nonetheless, research has shown these diets can contribute to small additional loss of kidney function, even for people with initially normal kidney function.
For people with impaired kidney function, diabetics with impaired kidney function, or for those with any clinical condition where loss of kidney function is already present, high-protein diets can accelerate the loss of kidney function. Studies show that for these cases, the annual loss of renal function may be 3%. According to other studies, a high-protein diet can accelerate the annual loss of kidney function by 3 to 5 times more than a diet with lower amounts of protein. All of this explains why a low-protein diet is recommended for those with chronic kidney disease (CKD) or at risk for CKD, such as diabetics or obese people with initial changes in urine tests (slightly elevated presence of urine albumin) and even people with a solitary kidney.
Dr. J.P.Merrill, one of the greatest nephrologist doctors, commented in one of his brilliant lectures that felines did not have kidney disease. He argued that felines eat a lot in a single meal and then went 3–4 days without feeding (he must have been talking about felines in the wild…). This would make the feline kidneys suffer from protein overload, followed by a resting period. According to the professor, this would protect the kidneys of these animals.
But what was Prof. Merrill’s suggestion for humans?
Although it is difficult to change human eating habits, he suggested that we concentrate protein intake to one of the meals of the day, aiming at making the kidneys only work hard once a day. This could ease the work of the kidneys and decrease the impact of the high-protein diet.
If you intend to start or have already started a high-protein diet, seek medical advice. Make sure to check with your doctor if this diet is suitable for your overall health, paying particular attention to its effects on your kidneys.
References:
- Kalantar-Zadeh, Kamyar, Holly M. Kramer, and Denis Fouque. “High-protein diet is bad for kidney health: unleashing the taboo.” (2020): 1–4.
- Glassock, Richard, Aleksandar Denic, and Andrew D. Rule. “When kidneys get old: an essay on nephro-geriatrics.” Brazilian Journal of Nephrology 39.1 (2017): 59–64.
