meldrego.com
All Articles | HomePage

(I am, in a way, an ongoing experiment: showing, in myself, albeit a test case of only one, how choosing to "do the right things" can make a difference to (my) ageing.  And yes, I eat a diet high in protein. And that's me, Mel Drego, up here.)

 

Recent headlines have claimed that eating less protein may slow ageing and extend lifespan. These claims stem largely from laboratory studies in worms, flies and rodents, and from research showing that reducing certain amino acids can influence biological pathways such as mTOR, IGF-1 and FGF21. 

While these findings are scientifically intriguing, they have often been extrapolated beyond what current human evidence supports. More importantly, they overlook one of the greatest threats to healthy ageing in humans: the progressive loss of skeletal muscle, known as sarcopenia, a topic I harp on regularly (hey, this site is about quality ageing!) in this site (meldrego.com) and its sister site groevolve.com

A careful examination of the scientific literature suggests that, for most older adults, the argument that "less protein is better" is not supported by the balance of human evidence. Rather than extending healthy lifespan, chronically inadequate protein intake can accelerate frailty, disability and loss of independence.

 

The Biology of Ageing: More Than Longevity

Discussions surrounding protein restriction often focus on lifespan. However, longevity is only one measure of successful ageing. Equally important is healthspan—the number of years lived free from disability and chronic disease, what I call in so many places "Quality Ageing" or "Quality of Life".

For older adults, preserving muscle mass is central to quality of life because skeletal muscle influences:

  • mobility and balance

  • insulin sensitivity

  • glucose disposal

  • immune function

  • recovery from illness

  • bone health, and

  • independence in daily living.

Loss of muscle mass is associated with increased falls , fractures, hospitalisation and mortality.

 

Why Protein Requirements Increase With Age

Ageing muscles become resistant to the normal anabolic effects of dietary protein, a phenomenon known as anabolic resistance. As a result, older adults require a larger amount of high-quality protein to stimulate muscle protein synthesis than younger adults.

The current Recommended Dietary Allowance (RDA) of 0.8 g/kg/day was designed to prevent deficiency in healthy adults—not to optimise muscle preservation during ageing. Hence, many expert groups recommend approximately 1.0–1.2 g/kg/day for healthy older adults, with even higher intakes (1.2–1.5 g/kg/day) for those with illness, frailty or who perform regular resistance exercise.

 

Human Evidence Strongly Links Low Protein Intake to Sarcopenia

Perhaps the strongest evidence against low-protein diets in older adults comes from research on sarcopenia.

A 2022 systematic review and meta-analysis involving more than 3,300 adults aged over 60 found that individuals with sarcopenia consistently consumed significantly less protein than those without sarcopenia. The authors concluded that inadequate protein intake is associated with increased risk of age-related muscle loss.

Similarly, a 2024 systematic review and meta-analysis of Korean older adults reported that consuming less than 0.8 g/kg/day was associated with significantly higher risks of sarcopenia and reduced hand-grip strength compared with intakes of 0.8–1.2 g/kg/day or higher.

These findings suggest that protein inadequacy may compromise one of the most important determinants of healthy ageing.

 

Muscle Is More Than Strength

Muscle functions as a major metabolic organ.

Healthy muscle:

  • removes glucose from the bloodstream

  • improves insulin sensitivity

  • stores amino acids during illness

  • produces beneficial signalling molecules (myokines)

  • supports immune function

Ironically, excessive protein restriction intended to improve metabolism helps reduce muscle mass, thereby worsening glucose regulation over time.

 

What About IGF-1 and mTOR?

Advocates of low-protein diets frequently cite reduced activation of mTOR and lower circulating IGF-1 as mechanisms for slowing ageing.

These pathways are regulators of cellular growth and longevity. However, in the argument for less protein, they are too often presented without sufficient context.

Both mTOR and IGF-1 are essential for:

  • muscle repair

  • wound healing

  • immune competence

  • maintenance of bone

  • adaptation to exercise

The question is therefore not whether these pathways should be "turned off," but whether they should be appropriately regulated.

Resistance exercise provides an elegant example. Exercise transiently activates mTOR, promoting muscle repair and adaptation, while simultaneously improving insulin sensitivity, mitochondrial function and overall health. Chronic overnutrition is biologically different from periodic activation associated with exercise and adequate protein intake.

 

Animal Studies Do Not Necessarily Translate to Humans

Much enthusiasm for protein restriction originates from studies in rodents and short-lived organisms.

These models have demonstrated that restricting total protein—or specific amino acids such as methionine—can extend lifespan.

However, important limitations exist:

  • rodents have very different metabolic rates

  • their lifespan differs dramatically from humans

  • laboratory animals live in controlled environments

  • muscle loss has different consequences

To date, there is no convincing long-term randomized trial demonstrating that chronically reducing protein intake extends human lifespan.

 

Protein Is Only One Part of the Equation

Another common misconception is that protein alone determines muscle health.

In reality:

Protein PLUS resistance training produces far greater benefits than either intervention alone.

Exercise sensitises muscle to dietary amino acids, allowing more efficient muscle protein synthesis.

Older adults who remain physically active and consume sufficient protein consistently maintain greater muscle mass and function than sedentary individuals consuming lower protein diets.

 

Protein Quality Matters

Not all protein sources are equal.

High-quality proteins containing adequate leucine stimulate muscle protein synthesis more effectively.

Excellent sources include:

  • dairy foods

  • eggs

  • fish

  • lean meats

  • soy

  • combinations of legumes and grains

Plant-based diets can absolutely support healthy ageing, provided total protein intake and essential amino acid intake remain sufficient.

 

Is High Protein Dangerous?

Healthy individuals often worry that higher protein intake damages the kidneys.

Current evidence does not support this concern in people with normal kidney function.

Protein restriction is appropriate in selected individuals with chronic kidney disease under medical supervision, but these recommendations should not be generalized to healthy older adults.

Likewise, concerns surrounding high protein often reflect diets rich in processed meats rather than well-balanced diets containing dairy, fish, legumes and lean protein sources.

 

A Balanced Perspective

Recent reviews have argued that moderate protein restriction may improve metabolic health in younger, sedentary adults by influencing nutrient-sensing pathways. These hypotheses deserve continued investigation. However, even those reviews acknowledge that older adults represent an important exception because preserving muscle becomes increasingly critical with age.

Ageing shifts nutritional priorities. For a healthy 30-year-old, reducing excess protein intake may have different implications than for a 75-year-old attempting to preserve strength, mobility and independence.

 

Finally...

The proposition that "less protein is better for ageing" oversimplifies a complex area of nutritional science.

Current human evidence does not support chronic protein restriction as a universal strategy for healthy ageing. Instead, inadequate protein intake is consistently associated with sarcopenia, reduced muscle strength, frailty and diminished physical function. Older adults exhibit anabolic resistance, making adequate protein intake even more important than in younger populations.

The strongest evidence suggests that healthy ageing is best supported not by indiscriminately reducing protein intake, but by combining adequate high-quality protein with regular resistance exercise, sufficient energy intake and an overall healthy dietary pattern.

Future research may refine our understanding of amino acid composition, meal timing and personalized nutrition. Until then, recommendations advocating broadly reduced protein intake for older adults should be interpreted with caution, as they risk undermining one of the most powerful protectors of healthspan: the preservation of skeletal muscle.

 

Mel Drego

=================================

References (APA 7)

Bauer, J., Biolo, G., Cederholm, T., Cesari, M., Cruz-Jentoft, A. J., Morley, J. E., Phillips, S., Sieber, C., Stehle, P., Teta, D., Visvanathan, R., Volpi, E., & Boirie, Y. (2013). Evidence-based recommendations for optimal dietary protein intake in older people: A position paper from the PROT-AGE Study Group. Journal of the American Medical Directors Association, 14(8), 542–559. https://doi.org/10.1016/j.jamda.2013.05.021

Beaudart, C., Dawson, A., Shaw, S. C., Harvey, N. C., Kanis, J. A., Binkley, N., Reginster, J.-Y., Chapurlat, R., Cooper, C., & Rizzoli, R. (2017). Nutrition and physical activity in the prevention and treatment of sarcopenia: Systematic review. Osteoporosis International, 28(6), 1817–1833. https://doi.org/10.1007/s00198-017-3980-9

Coelho-Junior, H. J., et al. (2022). Protein intake and sarcopenia in older adults: A systematic review and meta-analysis. International Journal of Environmental Research and Public Health, 19, 8718. https://doi.org/10.3390/ijerph19148718

Cruz-Jentoft, A. J., Bahat, G., Bauer, J., Boirie, Y., Bruyère, O., Cederholm, T., Cooper, C., Landi, F., Rolland, Y., Sayer, A. A., Schneider, S. M., Sieber, C. C., Topinková, E., Vandewoude, M., Visser, M., & Writing Group for the European Working Group on Sarcopenia in Older People 2 (EWGSOP2). (2019). Sarcopenia: Revised European consensus on definition and diagnosis. Age and Ageing, 48(1), 16–31. https://doi.org/10.1093/ageing/afy169

Deutz, N. E. P., Bauer, J. M., Barazzoni, R., Biolo, G., Boirie, Y., Bosy-Westphal, A., Cederholm, T., Cruz-Jentoft, A., Krznariç, Ž., Nair, K. S., Singer, P., & Calder, P. C. (2014). Protein intake and exercise for optimal muscle function with aging: Recommendations from the ESPEN Expert Group. Clinical Nutrition, 33(6), 929–936. https://doi.org/10.1016/j.clnu.2014.04.007

Han, M., Woo, K., & Kim, K. (2024). Association of protein intake with sarcopenia and related indicators among Korean older adults: A systematic review and meta-analysis. Nutrients, 16. https://doi.org/10.3390/nu16244306

Tournadre, A., Vial, G., Capel, F., Soubrier, M., & Boirie, Y. (2019). Sarcopenia. Joint Bone Spine, 86(3), 309–314. https://doi.org/10.1016/j.jbspin.2018.08.001

Additional Highly Relevant References

These are among the strongest papers supporting the case for adequate protein intake in ageing.

Morton, R. W., Murphy, K. T., McKellar, S. R., Schoenfeld, B. J., Henselmans, M., Helms, E., Aragon, A. A., Devries, M. C., Banfield, L., Krieger, J. W., & Phillips, S. M. (2018). A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength. British Journal of Sports Medicine, 52(6), 376–384. https://doi.org/10.1136/bjsports-2017-097608

Moore, D. R., Churchward-Venne, T. A., Witard, O., Breen, L., Burd, N. A., Tipton, K. D., & Phillips, S. M. (2015). Protein ingestion to stimulate myofibrillar protein synthesis requires greater relative protein intakes in healthy older versus younger men. The Journals of Gerontology: Series A, 70(1), 57–62. https://doi.org/10.1093/gerona/glu103

Phillips, S. M. (2017). Current concepts and unresolved questions in dietary protein requirements and supplements in adults. Frontiers in Nutrition, 4, 13. https://doi.org/10.3389/fnut.2017.00013

Phillips, S. M., & Fulgoni, V. L. (2016). Assessment of the protein quality of foods and implications for human health. Applied Physiology, Nutrition, and Metabolism, 41(5), 565–572. https://doi.org/10.1139/apnm-2015-0549

References Representing the Opposing View

To fairly address the argument, it is worth citing some of the literature that has motivated interest in protein restriction.

Fontana, L., & Partridge, L. (2015). Promoting health and longevity through diet: From model organisms to humans. Cell, 161(1), 106–118. https://doi.org/10.1016/j.cell.2015.02.020

Levine, M. E., Suarez, J. A., Brandhorst, S., Balasubramanian, P., Cheng, C.-W., Madia, F., Fontana, L., Mirisola, M. G., Guevara-Aguirre, J., Wan, J., Passarino, G., Kennedy, B. K., Wei, M., Cohen, P., Crimmins, E. M., Longo, V. D., & others. (2014). Low protein intake is associated with a major reduction in IGF-1, cancer, and overall mortality in the 65 and younger but not older population. Cell Metabolism, 19(3), 407–417. https://doi.org/**10.1016/j.cmet.2014.02.006**

This paper is particularly important because it found that the association reversed in adults over 65 years, with higher protein intake becoming protective—an important nuance often omitted in popular discussions