It's touted for its muscle-building and appetite-stimulating properties, but scientists worry that protein could be harmful to the arteries.
Researchers at the University of Pittsburgh showed that consuming more than a fifth of calories from protein can activate cells that clog arteries with plaque, a process that leads to a higher risk of strokes and heart attacks.
The team first showed in 2020 that protein could lead to hardened arteries, but recent research confirmed these findings using small human trials as well as experiments on mice and cells in a Petri dish.
It's because high-protein diets are at the peak of their popularity, which has been linked to the rise of fitness culture. Almost a quarter of the population gets over 22 percent of all daily calories from protein alone.
Dr. Babak Razani, a cardiologist who led the research, warned that their study suggests “higher” protein intake is “not a panacea” (stock image)
But Dr. Babak Razani, a cardiologist who led the research, warned that “higher” protein intake is “not a panacea” for good nutrition.
He suggested that people instead needed to eat a “balanced” diet with enough carbohydrates, fats and essential nutrients.
Americans are recommended to consume about 0.36 grams (g) of protein per pound of body weight daily.
For an average man weighing 199 pounds, that's about 71 grams per day – the equivalent of two chicken breasts or one and a half salmon fillets.
And for an average woman weighing 170 pounds, that's 61.2 g per day.
But fitness culture encourages consumption far more, with some plans suggesting doubling or even tripling that amount.
After consumption, protein is broken down into amino acids, which are used to repair torn muscle fibers and support the growth of new muscle fibers.
But when someone doesn't exercise, the unused proteins are filtered out of the body by the kidneys and excreted in the urine. The body cannot store proteins.
In the new study, published in the journal Nature Metabolism, scientists found that when the body breaks down high amounts of protein, it deactivates a type of white blood cell responsible for clearing cell debris called macrophages.
This leads to the accumulation of a “graveyard” of these cells within the vessel walls and the plaques to worsen over time.
The study initially gave 23 people high-protein meals or shakes and found that this led to an increase in levels of a particular amino acid, leucine.
This stimulates white blood cells and causes inflammation, which increases the risk of plaque buildup in the arteries.
In a separate part of the study, they also fed mice a high-protein diet – with up to 45 percent of calories coming from the macronutrient – and again found increases in leucine levels and activated white blood cells.
Dr. Bettina Mittendorfer, a metabolism expert at the University of Missouri who was also involved in the research, said: “We have shown in our mechanistic studies that amino acids, which are actually the building blocks of protein, can trigger disease through specific signals. “Mechanisms and then also change the metabolism of these cells.'
“For example, small immune cells in the vascular system, so-called macrophages, can trigger the development of arteriosclerosis.”
Dr. Razani added: “Perhaps blindly increasing protein load is wrong.” [especially in hospital patients].
“Instead, it is important to look at the diet as a whole and suggest balanced meals that do not unintentionally worsen cardiovascular disease, especially in people at risk for heart disease and vascular disease.”
But other scientists not involved in the research also railed against the study, saying more research was needed.
Dr. Duane Mellor, a nutritionist at Aston University in the UK, said: “Although these data are interesting, interpretation needs to be done carefully as this study only shows changes in plasma levels and…activation.” [white blood cells] after a single meal in humans
“The effect of daily food intake is not known from this human study.”
Dr. Bryan Williams, medical fellow at the British Heart Foundation, added: “Further studies over a longer period of time will help us better understand how protein affects our heart.”
“Eating a healthy diet, including consuming proteins in moderation, is still one of the most important things you can do for heart health.”
Limitations of the study include that it was only conducted on mice and over a short period of time, and the research now needs to be repeated in humans.
It's also not clear whether other factors, such as stress and other substances in the diet, could have driven plaque formation.
Dr. Robert Storey, a cardiologist at the University of Sheffield, UK, who was not involved in the study, said: “This research provides evidence that a high-protein diet could trigger reactions in the body that contribute to the risk of heart attack due to stroke.” a specific protein component that is present in higher amounts in animal proteins compared to plant proteins.
“We know that most heart attacks and strokes are caused by the buildup of fat in the blood vessels that supply the heart and brain.”
“They also show that leucine is the protein component that increases arterial calcification when fed to mice.”