Don't Make Protein Your Full-time Job

Protein has been a big focus in nutrition over the past few years. But new research suggests that people may be going overboard on the macronutrient – and scaling back could extend your life.

The scientific review, which was published in the Cell Press journal Cell Press Blue, analysed data from more than 350 studies on humans, mice, insects, yeast and other organisms, and found several biological mechanisms that suggest cutting back on protein could improve a person's health and lifespan. Among other things, a lower protein intake was linked to better metabolic function, nutrient signalling and cellular health.

However, protein is a macronutrient – one of the main nutrients your body needs to stay healthy – so you still definitely need some of it. Here's what the experts want you to keep in mind.

Why might scaling back on protein support healthy aging?

It's too early to say for sure. However, the researchers laid out a few different theories in their scientific review.

One piece of the puzzle seems to be fibroblast growth factor 21 (FGF21), a hormone that rises as protein intake drops. FGF21 can increase energy use, improve blood sugar management and reduce inflammation. The review cited mouse studies in which mice with higher levels of FGF21 lived longer than typical mice.

A trio of amino acids – methionine, isoleucine and valine – also seem to be a factor here. (Amino acids are the building blocks of protein.) Some research suggests that ingesting too many of these amino acids activates biological pathways that can increase the risk of obesity, inflammation and other health conditions linked with ageing.

Still, “it's hard to make a conclusion that you should limit protein intake,” says Dr Mir Ali, a bariatric surgeon. “Protein is important for overall health, and we still need to see a lot more research to determine the optimal protein intake for each stage of life,” he adds.

Lisa Moskovitz, a dietitian and the author of The Core 3 Healthy Eating Plan, agrees. “When research like this comes out that majorly contradicts what consumers are being told, it worries me that people will start to get overwhelmed again and go back into the all-or-nothing pitfall with healthy eating,” she says. “This study is interesting, but that doesn't mean you should throw away all your protein bars.”

What are current protein recommendations?

In Australia, the recommended dietary intake is 0.75 grams of protein per kilogram of body weight a day for women and 0.84 grams for men – about 46 grams a day for the average woman. Those figures, set by the National Health and Medical Research Council, rise after the age of 70, to 0.94 grams per kilogram for women and 1.07 grams for men.

Much of the recent noise about eating more protein has come out of the United States, where the latest dietary guidelines lifted the target to 1.2 to 1.6 grams per kilogram a day – up to double the previous recommendation of 0.8 grams. Australia has not followed.

And while the message that we're all falling short keeps circulating, the local data suggests otherwise. The Australian Bureau of Statistics found that almost all Australians – 98.5 per cent – were getting enough protein in 2023. The median intake for women was 75 grams a day, double the average requirement for women aged 30 to 64. The share of Australians getting more of their energy from protein than the recommended range has more than tripled since 2011–12.

“Many are taking the protein message overboard,” says Keri Gans, a dietitian and the author of The Small Change Diet.

Some groups need more protein than others

The researchers noted in the study that there are “many unknowns” about ideal protein intake. “While many individuals are likely eating substantially more than the recommended dietary allowance for protein and could benefit from protein or amino acid restriction, some individuals may have a greater demand for protein,” they wrote. Those with increased need include pregnant women, children, people following a kilojoule-restricted diet and people recovering from injuries, according to the study. Individuals who exercise may also have higher protein needs – or at least be able to take in more protein without seeing a negative impact on their health, the researchers wrote.

Additionally, this was a systematic review that analysed a series of studies, and each study had a slightly different definition of a ‘low’ protein intake. (For example, one study on rats had those in the high-protein group take in 20.4 per cent of their kilojoule intake from protein, while the low-protein group took in four per cent.) This made it difficult for the researchers to pinpoint what ‘low’ level of protein might be beneficial.

How to figure out your own protein needs

Experts say it may be helpful to consider your activity level and age when determining the right amount of protein for your needs. Active people usually need more protein than those who are inactive, Dr Ali says. But more research is needed to figure out exactly what those amounts are.

It can also be tricky to know if you're getting too little or too much protein based on how you feel, Dr Ali says. “Lack of protein may make you feel tired or weaker, but that's not always the case,” he says. “And, unless you have a kidney disorder or trouble metabolising protein, it's hard to overdo it.”

At a minimum, it's important to ensure you're getting an adequate amount of protein. “Protein, along with strength training, is important for preserving muscle mass, strength and independence as we age,” Keri says. “Cutting back too much could increase the risk of muscle loss, so this is not a reason to drastically reduce protein intake.”

Dr Ali agrees. “People still need protein,” he says.

If you're having trouble figuring out the right amount of protein for you, it may be helpful to consult your GP or an Accredited Practising Dietitian (APD). They can order tests to help determine whether you're meeting your needs, Dr Ali says.

Overall, Lisa recommends aiming for balance in your diet. “Overly obsessing or prioritising any one nutrient is never the answer,” she says. “Protein is still important, and eating too little can have deleterious health effects, but that doesn't mean you need to eat protein like it's your full-time job. The message here is everything in moderation.”