Eating a lot of protein is a trend. Some fitness websites recommend getting as much as 40 percent of your calories from protein. But isn’t that too much? New American research points in that direction: eating excessive protein could lead to arteriosclerosis.
The researchers are quite certain: increasing your protein intake “could be causing damage to your arteries,” says cardiologist Babak Razani of the University of Pittsburgh on the science website Eurekalert. In the study itself, in Nature Metabolism, that link is made less directly and with the necessary reservations. But the two research groups involved do show which mechanism has the potential to cause arteriosclerosis.
It has long been known that rabbits, mice, rats, hamsters and even monkeys develop thickenings in the blood vessel wall, so-called plaques, if they are fed a lot of protein. And it is clear: arteriosclerosis increases the risk of a heart or cerebral infarction. The American researchers had previously seen in mice that a high protein intake activates certain immune cells (macrophages) that play a role in plaque formation in the arteries. But what actually causes waste from these cells to not be cleaned up properly and to stick to the cell wall?
High protein experiment
To find out, fourteen test subjects took part in experiments with protein-rich food. In one meal, half of the energy consisted of protein. Another meal corresponded to the minimum intake of almost a quarter of Americans: 25 grams of protein in a meal, about 22 percent of the total energy in that meal.
Both eating moments resulted in an increased concentration of amino acids in the participants’ blood and both showed that the immune cells involved in plaque formation were activated. This involved monocytes, the precursors of macrophages, a certain type of white blood cells.
The amino acid leucine in particular turned out to be an important driver of this process. Leucine is an essential amino acid: the body does not produce this protein building substance itself, but obtains it from meat, dairy, nuts and legumes, among other things. Leucine is also contained in powders that many athletes take to maintain and build muscle mass.
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Speculating about the outcome
The blood samples did not show higher concentrations of fat (tryglycerides) – high cholesterol is a known risk for cardiovascular disease.
In new experiments with mice, the researchers saw that high protein consumption also initiated arteriosclerosis through this mechanism. They did not take that last step in humans, where they could see in culture dishes no more than the activation of the immune cells by amino acids – and could only speculate about the consequence: the development of plaques. This study also did not look at differences between animal and vegetable proteins.
Bram Slütter, who conducts research into arteriosclerosis and the immune system in Leiden, had already heard about this research at a conference. “It is interesting that they have looked at what proteins do on a certain type of immune cells at a fundamental level.” But he wouldn’t draw any big conclusions. “Everything happens faster with laboratory animals than with humans and you can isolate other factors. In humans, they only looked at blood values and the study was too short to say anything about the development of arteriosclerosis. You cannot simply extend the findings in mice to people.”
For large groups
This research should actually be conducted on large groups of people over a long period of time, says Slütter. “But with the resources they had, the researchers have painted a nice, complete picture.”
Although you cannot say that eating a lot of protein causes arteriosclerosis in people, something can be done with their observations, the researchers themselves write. Currently, 35 percent protein as a share of total energy intake is still considered acceptable. The Nutrition Center considers twice the recommended amount to be safe. And it is also recommended for people who want to lose weight, because protein satisfies better than other ‘macros’ (fat and carbohydrates).
Add to this the fact that most people already eat more than the minimum recommended amount of 0.8 grams per kilo of body weight (there is no upper limit in the Netherlands) and it is understandable that the researchers urge caution. Even though the risks, they themselves write, still have to be explored in larger groups, with different diets.