When appraising our diet, we tend to look at fats and carbs, especially sugars. But protein is also worth a look.

A 2018 report from the CSIRO looked at the benefits of eating protein for weight loss.

These included better appetite control, metabolic enhancement, reduced food cravings and improved body composition (more muscle, less fat).

But how much protein we actually need to get these results has been up for debate.

The CSIRO says “more recent research shows protein intakes should be personalised to an individual’s body weight”.

The CSIRO suggests that Australians aren’t getting enough quality protein in their diet. And that remains an issue.

But it’s made more complicated by startling new research that finds you can easily have too much protein.

University of Pittsburgh School of Medicine researchers have discovered that “excessive dietary protein could increase atherosclerosis risk”.

That is, too much protein causes heart disease

You probably know atherosclerosis as the build up of fats, cholesterol and other substances in and on the artery walls.

This build up is called plaque. The plaque can cause arteries to narrow, blocking blood flow. The plaque can also burst, leading to a blood clot.

The new research, though, showed that “consuming more than 22 per cent of dietary calories from protein can lead to increased activation of immune cells that play a role in atherosclerotic plaque formation, driving the disease risk”.

These findings came from small human trials and experiments in mice and cells in a Petri dish.

Further, the scientists showed that “one amino acid – leucine – seems to have a disproportionate role in driving the pathological pathways linked to atherosclerosis, or stiff, hardened arteries”.

In other words, they discovered the molecular mechanism that’s causing the trouble.

What the researcher says

Dr Babak Razani is professor of cardiology at Pitt, and senior and co-corresponding author of the new paper.

He said in a statement: “Our study shows that dialling up your protein intake in pursuit of better metabolic health is not a panacea. You could be doing real damage to your arteries.”

He said the researchers hope “that this research starts a conversation about ways of modifying diets in a precise manner that can influence body function at a molecular level and dampen disease risks”.

Early days

Dr Razani said many questions remain unanswered.

The big question: Is there a ‘sweet spot’ for maximising the benefits of protein – such as muscle gain – while avoiding kick-starting a molecular cascade of damaging events leading to cardiovascular disease?

He said the findings were particularly relevant in hospital settings, where nutritionists often recommend protein-rich foods for the sickest patients to preserve muscle mass and strength.

“Perhaps blindly increasing protein load is wrong,” he said.

“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.”

What to do?

As a guide, the CSIRO advises that the average Australian women weighs 71 kilograms, and requires 85 to 114 grams of protein per day for weight loss.

However, the Nutrient Reference Values for Australia and New Zealand, developed in 2006, recommends only 45 grams per day.

The average Australian man now weighs 86 kilograms and requires 103 to 138 grams of protein per day for weight loss. The recommended daily intake is only 64 grams of protein a day.

Given that most adults eat and drink up to three kilograms of foods and liquid a day, the CSIRO protein intake is well within a safe range.

But, according to a 2018 paper from the University of Sydney: “In Australia and New Zealand the acceptable macronutrient distribution range (AMDR) is 15 to 25 per cent of energy …”

All up, this suggests that those of us eating at the top end of this range are potentially at a higher risk of heart disease.