It has been hyped up for its muscle-building and appetite suppressing qualities, but scientists fear that protein could be bad for your arteries.
Researchers at the University of Pittsburgh found that mice fed diets high in the macronutrient had dangerous levels of plaque linked to strokes and heart attacks.
They suggested this had been caused by high protein levels causing dysfunction in the immune system, leading to white blood cells collecting inside artery walls and causing fatty deposits to build up.
It comes as high protein diets are at the height of the popularity, which has been linked to the rise in gym culture.
Dr Babak Razani, a cardiologist who led the research, warned their study suggested that ‘dialing up’ protein intake was ‘not a panacea’ (stock image)
Dr Babak Razani, a cardiologist who led the research, warned their study suggested that ‘dialing up’ protein intake was ‘not a panacea’ for a good diet.
He suggested that, instead, people need to ensure they are eating a ‘balanced’ diet containing enough carbohydrates, fats and vital nutrients.
Americans are advised to eat about 0.36 grams (g) of protein per pound of body weight per day.
For the average man at 199lbs, this is about 71g per day — equivalent to two chicken breasts or one-and-a-half salmon fillets.
And for the average woman who weighs 170lbs, this is 61.2g per day — equivalent to one-and-a-half tuna steaks or two cups of chickpeas.
But gym culture promotes consuming far more, with some plans suggesting double this amount — or about 0.8g per pound of bodyweight per day.
Once consumed, the protein is broken down into amino acids which are used to repair torn muscle fibers and to help to grow new ones.
But if someone is not working out, then the unused proteins are filtered out of the body by the kidneys and excreted in the urine. The body cannot store protein.
In their theory, revealed in the journal Nature Metabolism, the scientists warned that a high level of protein in the diet could activate macrophages — a type of white blood cell responsible for clearing out cellular debris.
They suggested that these activated cells would not function correctly, however, and instead collect in ‘graveyards’ inside artery walls.
Their study — which involved giving humans a protein shake and mice a high-protein diet — showed that after consuming these meals levels of one amino acid, leucine, surge in the bloodstream.
This stimulated white blood cells and caused inflammation, they said, which could cause the formation of plaques.
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 really the building blocks of the protein, can trigger disease through specific signaling mechanisms and then also alter the metabolism of these cells.’
‘For instance, small immune cells in the vasculature called macrophages can trigger the development of atherosclerosis.’
Dr Razani added: ‘Perhaps blindly increasing protein load is wrong [especially in hospital patients].
‘Instead, it’s important to look at the diet as a whole and suggest balanced meals that won’t inadvertently exacerbate cardiovascular conditions, especially in people at risk of heart disease and vessel disorders.’
Limitations of the study include that it has only been carried out in mice and over a short period, with the research now needing to be repeated in humans.
It is also not clear whether other factors, such as stress and other substances in the diet, could have driven the build up of plaques.
Dr Robert Storey, a cardiologist at the University of Sheffield, UK, who was not involved in the paper, said: ‘This research provides evidence that a high-protein diet might trigger responses in the body that contribute to the risk of heart attack or stroke as a result of a particular component of protein that is present at higher quantities in animal protein compared with plant proteins.
‘We know that the majority of heart attacks and strokes are caused by the build-up of fat in the blood vessels supplying the heart and brain.
‘They also show that leucine is the component of protein that increases furring in the arteries when fed to mice.’