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 showed consuming over a fifth of calories from protein can activate cells which clog up the arteries with plaque – a substance that damages the vessels, disrupting blood flow.
A lack of healthy blood flow around the body leads to a higher risk of strokes and heart attacks.
The latest research confirmed findings from previous lab research, and added new evidence using small human trials and experiments in mice and cells in a petri dish.
It comes amid the booming popularity in high protein diets linked to the rise in gym culture. Nearly a quarter of the population receives over a fifth of their total daily calories from protein alone.
Dr Babak Razani, a cardiologist who led the research, warned their study suggested that ‘dialing up’ protein intake was ‘not a panacea’ (stock image)
But Dr Babak Razani, a cardiologist who led the research, warned 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.
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For the average man at 199lbs, this is about 71g per day — equivalent to about 12 percent of daily calories, two chicken breasts or one-and-a-half salmon fillets.
And for the average woman who weighs 170lbs, this is 61.2g per day or 10 percent of daily calories.
But gym culture promotes consuming far more, with some plans suggesting double or even triple this amount.
Once consumed, 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 exercising, the unused proteins are filtered out of the body by the kidneys and excreted in the urine.
In the new study, published in the journal Nature Metabolism, the scientists found that when the body breaks down high levels of protein, it activates a type of white blood cell responsible for clearing out cellular debris, known as macrophages.
This leads to the accumulation of a ‘graveyard’ of those cells inside the vessel walls and the worsening of plaques overtime.
The study first administered high protein meals or shakes to 23 people and tested their blood just before the meals and at one and three hours afterward. Each had fasted for 12 hours beforehand.
Results showed that protein consumption caused a rise in a particular amino acid, leucine, and an uptick in a substance that activates the immune system.
The scientists suggested that with more immune cells activated, this would have raised inflammation levels — increasing the risks of plaques.
In a separate part of the study, they also fed mice on a high protein diet — with up to 45 percent of its calories from the macronutrient — and tested their blood.
This also showed a spike in levels of leucine and a rise in a substance which activates 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 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 called macrophages can trigger the development of atherosclerosis [plaques in the arteries].’
Dr Razani added: ‘Perhaps blindly increasing protein load is wrong.
‘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.’
But other scientists not involved in the research have railed against the study, saying that more research is needed.
Dr Duane Mellor, a dietician at Aston University in the UK, said: ‘The effect of a day’s food intake is not known from this study in humans.’
Dr Bryan Williams, a medical officer at the British Heart Foundation, added: ‘Further studies over a longer period of time will help us better understand how protein affects our heart.
‘A healthy diet, which includes eating protein in moderation, is still one of the most important things you can do for heart health.’
Limitations of the study include that it was carried out over a short period and that it involved a small sample size.
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.’