We are often told to eat more protein to maintain a healthy and balanced diet. But new research shows that eating too much can actually be harmful to your health.

Protein is an essential macronutrient and is important for growing and maintaining muscle mass. It has also been proven to reduce appetite and boost metabolism. However, the amount of protein our bodies actually need to perform these functions is much lower than modern marketing would lead you to believe.

All proteins are made up of a series of individual units called amino acids, like beads on a string. Each amino acid has unique properties and is present at varying levels from different protein sources.

In a new study published in the journal natural metabolismresearchers found that consuming too much of a certain amino acid called leucine may increase the risk of cardiovascular disease.

“We first became interested in this topic because high-protein diets are popular with both clinicians, nutritionists, and the general public for weight loss, building muscle mass, and overall metabolic health. ,” said co-author Babak Razani, professor of medicine and chair of cardiology. he said at the University of Pittsburgh School of Medicine. newsweek. “However, there are large, well-conducted epidemiological studies (based primarily on dietary questionnaires) showing that increased protein intake is correlated with cardiovascular disease.”

In 2020, Razani’s team published a paper in mice showing that a high-protein diet is associated with an increased risk of atherosclerosis, a buildup of fat, cholesterol and other substances inside and outside the walls of arteries. showed that.

“We went further and uncovered the exact mechanism: Protein intake fills the bloodstream with amino acids,” the study says. “Immune cells called macrophages are important drivers of atherosclerosis and take up amino acids. [which is sensed by] important [molecule] It’s called mTOR. mTOR initiates deleterious signaling pathways within macrophages, leading to dysfunction and, in turn, exacerbation of atherosclerosis. ”

In other words, a high-protein diet activates a molecular machine called mTOR, which activates immune cells and can increase the accumulation of fat and cholesterol within artery walls.

“In this study, we tested the responses of these proteins, amino acids, and immune cells in real human studies and found that human immune cells react in exactly the same way as they did in animal studies.” said Professor Razani.

One amino acid in particular appears to drive this signaling pathway.

“Many amino acids increase in the bloodstream after ingesting protein, which activates mTOR and harmful signaling pathways in macrophages, immune cells that are the main cause of atherosclerosis (or cardiovascular disease). We found that it was primarily leucine that oxidized,” Razani said.

But how much protein do we need to consume to trigger this response?

“We used different doses of protein in the form of smoothies and mixed meals to get an estimate of the protein intake needed to activate immune cells,” Razani said. “It turned out to be about 22 percent [of total] kilocalorie intake. For reference, the USDA recommends a balanced diet with 15 calories of protein, healthy fats and complex carbohydrates, which largely reflects the Mediterranean diet. ”

Of course, different protein sources have different concentrations of leucine.

“Some animal proteins, like whey, which many of the protein powders sold in nutrition stores are made of, have high leucine content,” Razani says. “But overall [i.e. in whole meats]the difference in leucine content between animal and vegetable proteins is not very large.

“The more complex issue lies in how these proteins are digested and absorbed, and the kinetics of leucine entering the bloodstream. We’re working on this issue. We’re talking about it.”

Further research is also needed to understand the true impact of dietary protein on human health.

“It’s clear that long-term human studies are needed to influence dietary guidelines, but for overall metabolic health, blindly increasing your protein intake in your diet is the answer. The important message is that this is not the case,” Razani said. “As a cardiologist, I still encourage people to follow the Department of Agriculture’s nutritional recommendations. This diet is a Mediterranean diet that combines about 15 calories of dietary protein per day with healthy fats and complex carbohydrates. It is one of the most balanced diets for a vast majority of the population.

“Additionally, you should not take our study results with a grain of salt and make major changes to your diet without consulting your doctor, especially if you already have cardiovascular disease. It should increase debate on the topic and stimulate the nutritional, metabolic, and medical communities.”Such mechanistic studies need to be conducted to provide a more comprehensive understanding of the role of diet in heart health. ”