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Moderate protein intake from a range of plant- or animal-based sources could help you live longer, a new study suggests. Jordan Lye/Getty Images
  • A new study in mice suggests that consuming a moderate amount of protein may be most conducive to improved metabolic health.
  • In the study, the sweet spot for moderate protein consumption was between 25% and 35% of a mouse’s daily diet.
  • Older people need more protein due to the body no longer being able to process the macronutrient efficiently.

It only makes sense that a person’s nutritional needs change as they go through life from childhood through adulthood. As we grow, reach maturity, and age, our bodies are occupied with different tasks.

As researchers seek to extend our healthy lifespans — periods free of serious disease — they have been hoping to identify the optimal balance of macronutrients that promote good health at each life stage.

A new study of mice investigates the role of protein at different stages of life.

The study finds that consuming moderate amounts of protein in youth and middle age may be the key to good metabolic health.

The study is published in Geroscience.

Using a mouse model, the researchers studied the effects of protein intake on biological aging.

They fed young (6-month-old) and middle-aged (16-month-old) mice diets with varying levels of protein for two months.

Their diets consisted of 5%, 15%, 25%, 35%, or 45% protein. The moderate amounts identified in the study were 25% and 35%.

All mice were fasted for three hours before being euthanized for tissue harvesting and analysis.

In mice, a diet low in protein resulted in the development of fatty liver, and middle-aged mice exhibited higher levels of lipids, or fats, in their systems than younger mice. The moderate-protein diets also lowered lipid and blood sugar levels in the mice.

A moderate-protein, therefore, was equated to improved metabolic health in mice.

As to whether the study’s findings will carry over to humans, Stuart Phillips, PhD, a professor at McMaster University, told MNT that it’s “always hard to know, but as short-lived mammals, mice are a proxy for humans, but much of what’s seen in mice may not be readily translatable to humans.”

Conner Middlemann, the nutritionist behind Modern Mediterranean, said she felt the study nonetheless had value.

“Even though this is a mouse study, it reinforces my view that most of us — especially anyone over 50 — stand to benefit from getting around 25% of the energy we consume from protein. This is significantly more than the average American currently consumes. Some people need even more protein.”

– Conner Middlemann, nutritionist

Of special note are people practicing resistance training. To maximize lean mass, the average required amount, Conner said, is about 1.6 grams per kilogram of body weight, and “some people may need 2.2 g/kg or more.”

For people wishing to burn fat while still retaining muscle, 1.6 to 2.4 grams per kilogram may be in order.

Middlemann explained to MNT that older people require more protein than younger individuals.

“Sarcopenia is the primary age-related cause of frailty, which is associated with a higher risk of disabilities, having to go to a nursing home, and of falls, fractures, hospitalizations, and premature death,” Middlemann said.

It occurs with age-related muscle loss, she said, ranging “anywhere from 0.5% to 2% of total muscle mass each year, starting around age 50 (though in folks who are largely inactive, it can start even earlier).”

Middlemann added said that her clients have been able to increase “muscle mass, cardio-metabolic health, and overall quality of life” by consuming 25–35 grams of protein at each meal and practicing resistance training.

Protein is critical at all stages of life.

“The word ‘protein’ is derived from the Greek word proteios, meaning ‘first’ or ‘primary,’ which reflects its top-drawer status in human nutrition,” Middlemann noted.

Dr. Phillips explained protein’s importance:

“When we’re growing, protein provides the building blocks (amino acids) to make new bones, skin, teeth, muscles, etc. Basically, every tissue requires protein to grow. Once we’re fully grown, protein still provides building blocks — it’s not for growth, but to replace proteins that are being turned over (broken down). Body protein turnover happens during our entire lives.”

In the United States, the required daily amount (RDA) of 0.8 grams of protein per kilogram of body weight falls far short of the body’s actual needs, said Middlemann. She clarified that the figure represents only the required amount of protein to avoid malnutrition, not the amount to promote good health.

Middlemann noted that the RDA is a holdover from a time when nitrogen-balance studies that are no longer considered valid formed the foundation of such recommendations. She said one could get a more accurate understanding of nutritional needs using the Indicator Amino Acid Oxidation (IAAO) technique.

The IAAO technique, said Middlemann, provides a more reasonable daily recommendation. It suggests 1.2 grams of protein per kilogram of body weight is appropriate for healthy young men, older men, and older women.

The difference between the two recommendations is significant. The RDA for a 150-pound person is 54 g of protein daily, while according to IAAO measurement, it would rise to 81 g of protein.

But can one consume too much protein?

“We have a high capacity to digest and absorb protein, so I’m not sure you can get so much that it’s ‘too much’,” said Dr. Phillips.

He noted that some have suggested an excess of protein can lead to kidney and bone issues, “but those are largely debunked.”

“For the most part, proteins are relatively equal, but an axiom that’s true is that animal-derived protein is higher quality than plant-derived protein,” Dr. Phillips noted but added “Most work shows that this difference is likely quite small.”