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 build-ups of plaque in their arteries.
They suggested this had been caused by high protein levels causing dysfunction in the immune system, leading to white blood cells collecting in ‘graveyards’ inside artery walls and causing fatty deposits to build up.
It comes as a high protein diet becomes ever more in demand, with bars, cereals and yogurts hitting the shelves that claim their high protein content helps them build muscle.
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 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.
This would cause fatty deposits to start to build-up within them and a plaque to emerge — linked to atherosclerosis.
In particular, they suggested the amino acid leucine — one of the three types — could trigger the troublesome activation.
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 results now needed from humans to confirm the findings.
It is also not clear whether other factors, such as stress or other substances in the diet, could have been involved in the build-up of plaques in the blood vessels of mice.
