Does the Protein You Eat in Midlife Influence How Well You Age?

1. Higher protein intake in midlife was associated with healthy aging, but the associations differed by protein source

Of the 48,762 women, 3,721 (7.6%) met all four criteria for healthy aging approximately three decades later.

In the fully adjusted analyses, every additional 3% of daily energy from protein was associated with:

5% higher odds of healthy aging for total protein,

7% higher odds for animal protein,

14% higher odds for dairy protein,

38% higher odds for plant protein.

These estimates came from models that accounted for multiple demographic, lifestyle and health factors. The models for individual protein sources also accounted for other protein sources.

The results therefore suggest that the relationship between protein intake and later healthy aging varied substantially according to protein source.

2. Plant protein showed the strongest association with overall healthy aging

The strongest association was observed for plant protein.

For every additional 3% of daily energy coming from plant protein, the odds of meeting the complete healthy-aging definition were 38% higher in the fully adjusted model.

The association remained statistically significant in multiple sensitivity analyses, including analyses using protein intake expressed in grams per day or grams per kilogram of body weight.

The association was weakened after adjustment for fruit and vegetable intake but remained statistically significant. This suggests that other characteristics of plant-based foods may contribute to the observed relationship.

3. Plant protein was particularly associated with preserved physical function

When the four components of healthy aging were examined separately, the strongest result for plant protein concerned physical function.

Every additional 3% of daily energy from plant protein was associated with 41% higher odds of having no physical-function limitations in the fully adjusted model.

Plant protein was also associated with 16% higher odds of good mental health.

In contrast, after full adjustment, plant protein was not significantly associated with being free of the 11 chronic diseases or with absence of memory complaints.

Animal protein showed a smaller positive association with preserved physical function: 5% higher odds per additional 3% of energy.

4. Replacing other nutrients with plant protein was associated with better outcomes

The researchers also performed isocaloric substitution analyses. These models estimate what happens statistically when calories from one nutrient are replaced with the same number of calories from another.

Replacing 3% of daily energy from several other nutrient sources with plant protein was associated with approximately 22% to 58% higher odds of healthy aging, depending on what was replaced.

Favorable associations were observed when plant protein replaced animal or dairy protein and several sources of dietary fat.

Plant protein substitutions were also associated with better physical-function outcomes. Replacing calories from the other macronutrients examined with equivalent calories from plant protein was associated with approximately 20% to 60% higher odds of having no physical limitations.

These analyses are important because they examine protein within the context of the whole diet. Eating more of one nutrient necessarily changes the relative contribution of another.

5. The findings were robust, but they do not establish causality

The study had several important strengths. It included almost 49,000 women, assessed diet before older age and separated dietary assessment from the final health evaluation by approximately three decades.

The researchers also performed multiple sensitivity analyses. The overall pattern of findings remained similar when protein intake was evaluated in different ways and when alternative measures of physical and cognitive function were used.

However, this was an observational study. It cannot demonstrate that increasing plant protein causes healthier aging.

Residual or unmeasured confounding remains possible. Plant-protein foods contain other potentially beneficial components, including fiber, micronutrients and polyphenols, which may partly explain the associations.

The population was also predominantly White women who were registered nurses. The findings therefore require confirmation in men and more diverse populations.

This study addresses an important question in longevity medicine: how early can nutrition be associated with health decades later?

The women were in midlife when their protein intake was assessed. Healthy aging was evaluated approximately 30 years later, when participants were in older adulthood.

The outcome also went beyond lifespan. Healthy aging required survival together with freedom from major chronic disease and preservation of physical, cognitive and mental health.

The results suggest that protein should not be considered only in terms of total grams consumed.

Protein source and the foods providing that protein may also be important for long-term health.

Plant protein showed the strongest association with the overall healthy-aging outcome and particularly with preserved physical function.

The findings support including plant sources of protein as part of a healthy dietary pattern across adulthood.

They do not show that animal protein should be eliminated. Animal protein was also positively associated with overall healthy aging after full adjustment and showed a modest positive association with preserved physical function.

Nor does this study establish an optimal amount of protein or an ideal ratio of plant to animal protein.

The study also cannot separate the effect of plant protein itself from the complete nutritional profile of plant foods. Foods providing plant protein also contain fiber, micronutrients and bioactive compounds, and the authors specifically acknowledge that these may contribute to the observed associations.

A separate clinical question becomes increasingly important with age: how much protein is needed to preserve muscle mass and function, and can increasing protein intake help when muscle has already been lost?

Answering that question requires intervention studies and evidence examining protein together with resistance exercise.