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Is moderate protein diet the key to youth as we age?

A new study in mice suggests that improved metabolic health may be most conducive to us when a moderate amount of protein is consumed.

In the study, the sweet spot for moderate protein consumption was found to be between 25% and 35% of a mouse’s daily diet.
More protein is needed by older people due to the macronutrient no longer being efficiently processed by the body.

It only makes sense that nutritional needs change as individuals go through life, from childhood through adulthood. As we grow, reach maturity, and age, different tasks occupy our bodies.

As researchers seek to extend our healthy lifespans — periods free of serious disease — the optimal balance of macronutrients that promote good health at each life stage is being sought.

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

The study concludes that good metabolic health may be promoted by consuming moderate amounts of protein in youth and middle age.

How is biological age affected by protein?


In a mouse model, the effects of protein intake on biological aging were studied by the researchers.

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

Diets consisting of 5%, 15%, 25%, 35%, or 45% protein were provided to them. 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, the development of fatty liver was observed with a diet low in protein, and higher levels of lipids, or fats, were found in the systems of middle-aged mice compared to younger ones. The moderate-protein diets also led to a reduction in lipid and blood sugar levels in the mice.

Improved metabolic health in mice was thus associated with a moderate-protein diet.

Can protein potentially extend human lifespans?


Regarding whether the study’s findings will be applicable to humans, Stuart Phillips, PhD, a professor at McMaster University, mentioned to MNT that it’s “always hard to know, but as short-lived mammals, mice are a proxy for humans, though much of what’s observed in mice may not be easily transferable to humans.”

Conner Middlemann, the nutritionist behind Modern Mediterranean, expressed the opinion that the study still holds value.

“Even though this is a mouse study, it reinforces our view that most of us — especially those over 50 — could benefit from obtaining around 25% of our energy from protein. This is considerably more than what the average American currently consumes. Some individuals may require even higher protein intake.”

Notably, individuals engaging in resistance training have specific considerations. To optimize lean mass, Conner stated that the average required amount is approximately 1.6 grams per kilogram of body weight, with “some individuals potentially needing 2.2 g/kg or more.”

For those aiming to burn fat while preserving muscle, a protein intake ranging from 1.6 to 2.4 grams per kilogram might be advisable.

More protein is needed by older adults.


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

“Sarcopenia is the primary cause of frailty related to age, and it is associated with a higher risk of disabilities, the need for nursing home care, falls, fractures, hospitalizations, and premature death,” Middlemann said.

Age-related muscle loss is the underlying factor, she noted, occurring at a rate ranging “from 0.5% to 2% of total muscle mass per year, starting around age 50 (although it can begin even earlier in largely inactive individuals).”

Middlemann further mentioned that “muscle mass, cardio-metabolic health, and overall quality of life” have been improved in her clients by the consumption of 25–35 grams of protein at each meal and the practice of resistance training.

The significance of protein consumption


Protein holds critical importance throughout our lifespan.

“The term ‘protein’ finds its origins in the Greek word proteios, signifying ‘first’ or ‘primary,’ highlighting its paramount status in human nutrition,” as observed by Middlemann.

The significance of protein was elaborated upon by Dr. Phillips:

“During our growth phase, protein supplies the fundamental building blocks (amino acids) needed for the formation of new bones, skin, teeth, muscles, and more. Essentially, every tissue relies on protein for growth. Even after we reach full maturity, protein continues to provide building blocks — not for growth but for the replacement of proteins undergoing turnover (breakdown). Body protein turnover occurs throughout our entire lifetime.”

In the United States, the recommended daily intake (RDA) of 0.8 grams of protein per kilogram of body weight is insufficient to meet the actual requirements of the body, as mentioned by Middlemann. It should be noted that this figure solely represents the minimum protein intake necessary to prevent malnutrition and does not encompass the amount necessary for promoting good health.

How much protein do we need?


Middlemann pointed out that the RDA is a remnant of a time when recommendations were primarily based on nitrogen-balance studies that are no longer considered valid. She mentioned that a more accurate understanding of nutritional needs can be obtained through the Indicator Amino Acid Oxidation (IAAO) technique.

According to Middlemann, the IAAO technique provides a more reasonable daily recommendation. It suggests that 1.2 grams of protein per kilogram of body weight are suitable for healthy young men, older men, and older women.

The contrast between the two recommendations is significant. The RDA for a 150-pound individual is 54 g of daily protein, while the IAAO measurement indicates it should be raised to 81 g of protein.

But can one consume an excess of protein?


“We possess a high capacity for digesting and absorbing protein, so it’s uncertain whether you can have so much that it becomes ‘excessive’,”

– as stated by Dr. Phillips.

He mentioned that there have been suggestions that an excess of protein might lead to kidney and bone issues, “but most of those claims have been debunked.”

“For the most part, proteins exhibit relatively similar qualities, but it’s worth noting that animal-derived protein is generally considered of higher quality than plant-derived protein,”

Dr. Phillips acknowledged, while also adding,

“Most research indicates that the difference is likely quite minimal.”