Clinical Guide to Protein’s Effects on the Brain and Cognition

Valeria Medina, NeuronUP neuropsychologist, reviews the scientific evidence on the protein craze and its real effects on brain health and cognition.

The rise of “proteinization” in eating habits

In just a few years, protein has gone from being associated almost exclusively with bodybuilding to becoming one of the major symbols of healthy eating. The “high protein” label now appears on cereals, breads, desserts, snacks, and drinks, and for many people it functions as an automatic seal of quality.

The phenomenon reflects the rise of strength training, concerns about body composition, fear of losing muscle mass with age, and the popularity of satiating diets. In 2025, 70% of surveyed U.S. consumers said they were trying to eat more protein, and 23% reported following a high-protein diet. “Good source of protein” also became the most frequently selected criterion for defining a healthy food. The industry has responded with fortified products, although a food does not become healthy just because it includes the word “protein”. Its value depends on its overall composition, degree of processing, and the needs of the person consuming it (Clinthorne et al., 2026).

Protein is essential: why more is not always better

Protein provides essential amino acids, contributes to tissue repair, maintains muscle mass, and is part of enzymes, hormones, and antibodies. Some amino acids also act as neurotransmitters or as precursors to serotonin, dopamine, norepinephrine, glutamate, GABA, and glycine, so their role goes far beyond muscle (Kim et al., 2025). 

Adequate intake can promote satiety, help preserve lean mass during weight loss, and support muscle protein synthesis when combined with strength training. These benefits are especially relevant for athletes, older adults, people at risk of sarcopenia, and those following a calorie-restricted diet (Clinthorne et al., 2026). The problem arises when a context-specific benefit becomes a universal recommendation. Supplementation alone has modest effects on strength and performance in the absence of training. For a sedentary person who already meets their needs, increasing protein is likely to provide little additional benefit (Kim et al., 2025).

It is also important to distinguish between adequacy and excess. Needs vary with age, activity level, pregnancy, illness, and risk of muscle loss. Therefore, an amount that is adequate for a young, sedentary person may not be sufficient for an older adult or someone who strength trains frequently (Knopf & Lamming, 2026).

What does the scientific evidence say about high-protein diets?

Evidence on the metabolic and longevity effects of protein

Observed benefits of high protein intake

One of the best-known effects of high-protein diets is increased satiety. By reducing hunger and making it easier to control food intake, they may promote weight loss as part of a calorie-restricted diet. In this context, they also help preserve fat-free mass and may produce a slight increase in energy expenditure (Kim et al., 2025).

High intake may also be useful when there is an adequate muscle-building stimulus. Combined with strength training, greater amino acid availability promotes muscle protein synthesis and recovery. This effect is especially important for athletes and physically active people, but also for older adults, who have a lower anabolic response and a greater risk of losing muscle mass with age (Clinthorne et al., 2026).

Observed adverse effects of high protein intake

Some observational studies, such as Kim et al. (2025), have shown that the effects described above diminish when high intake is not accompanied by exercise, calorie restriction, or increased physiological needs. For sedentary people who already meet their requirements, adding more protein has little impact on muscle mass, strength, and performance. Likewise, high animal protein intake has been linked to an increased risk of type 2 diabetes, cancer, or mortality. These associations are not consistent and may depend on age, health status, physical activity, and the type of food from which the protein comes. There is also a risk that a protein-centered diet will displace other important foods. If fruit, vegetables, whole grains, or legumes are excessively reduced to increase protein intake, consumption of fiber, vitamins, minerals, and bioactive compounds necessary for metabolic health may decline.

In experimental models, high availability of amino acids such as methionine, leucine, isoleucine, and other branched-chain amino acids can continuously activate pathways associated with cell growth, including mTORC1. This activation has been linked to insulin resistance, reduced autophagy, and processes associated with aging, although its direct relevance in humans has not yet been fully established (Knopf & Lamming, 2026).

Similarly, high protein intake could be associated with less favorable effects in middle age, while at older ages it may protect against sarcopenia, frailty, and malnutrition (Kim et al., 2025).

Evidence on the effects of protein on the brain

Observed benefits of high protein intake

Protein provides the amino acids needed to maintain neuronal structure and produce neurotransmitters. Tyrosine and tryptophan contribute to the synthesis of dopamine, norepinephrine, and serotonin, while other amino acids are involved in the glutamate, GABA, and glycine systems, all of which are essential for brain communication (Nagao, 2024). 

Branched-chain amino acids also contribute to glutamate regulation. This neurotransmitter plays a central role in synaptic plasticity, learning, and memory, so adequate amino acid availability could contribute to maintaining these processes (Coelho-Júnior et al., 2021).

Structurally, a longitudinal study using UK Biobank data found that a higher proportion of animal protein was associated with less reduction in hippocampal volume. The relationship also emerged when comparing the proportions of animal and plant protein, and was especially favorable among those who ate fish and shellfish (Cui et al., 2024).

Some interventions involving protein-rich foods have also observed improvements in blood flow in brain regions related to memory and psychomotor speed. These changes were described mainly in studies of nuts and soy, although the foods analyzed contained nutrients other than protein (Adams et al., 2025).

Observed adverse effects of high protein intake

Total protein intake has not been consistently associated with better preservation of brain structure. The UK Biobank study found no significant associations with total brain volume, gray matter, white matter, or white matter hyperintensities. The findings were almost exclusively concentrated in the hippocampus. In addition, the observed associations were not always linear. In some analyses, increasing intake above certain levels did not produce additional benefits, so it cannot be assumed that more protein provides greater brain protection (Cui et al., 2024).

Nor can these findings be attributed to protein alone. Fish provides omega-3 fatty acids, nuts contain unsaturated fats and polyphenols, and other protein-rich foods can provide vitamins and minerals with their own effects on brain health (Adams et al., 2025).

Amino acid availability must also remain balanced. Glutamate is essential for neurotransmission, but an excessive extracellular concentration can cause excitotoxicity and neuronal damage. Therefore, the relationship between protein and the brain cannot be reduced to the idea that greater amino acid availability is always beneficial (Coelho-Júnior et al., 2021).

So far, there are few studies on long-term consumption of high-protein diets, concentrated supplements, or fortified foods and their effects on brain structure. Nor is there a specific recommended amount to prevent atrophy, Alzheimer’s disease, or other neurodegenerative diseases (Nagao, 2024).

Evidence on the cognitive effects of protein

Observed benefits of high protein intake

Studies on cognition have found some favorable effects, although not consistently. A review of clinical trials found improvements in psychomotor speed in three of nine studies that compared a protein intervention with a control without protein or with a lower amount. Positive results were found with peanuts, soy nuts, and milk protein concentrate. 

Studies on cognition (Adams et al., 2025) have found some favorable effects, although not consistently:

• Improvements have been reported in working memory, declarative memory, and visuospatial memory, mainly after eating walnuts, peanuts, or mixed nuts.
• These findings suggest that certain protein-rich foods could have a favorable influence on specific cognitive domains, although their effects cannot be attributed to protein alone.
• In clinical populations, some findings have been more pronounced: protein-calorie supplementation improved global cognition in people with subacute stroke, while an intervention with lactoferrin was associated with better scores in patients with Alzheimer’s disease. 

In older adults without dementia, some studies have found positive associations between higher protein intake and memory, visuospatial skills, verbal fluency, processing speed, and sustained attention (Coelho-Júnior et al., 2021).

Over the long term, a prospective study involving more than 77,000 participants found that higher total, animal, and plant protein intake was associated with a lower likelihood of subjective cognitive decline. The most favorable associations were found with legumes, fish, and lean poultry, as well as when some carbohydrates or animal protein were replaced with plant protein (Yeh et al., 2022).

Observed adverse effects and limitations of high protein intake

Despite these findings, most trials in healthy adults found no overall improvements in attention, executive function, memory, or global cognition. Positive effects were limited to specific tests, foods, and participant groups (Adams et al., 2025).

The meta-analysis by Coelho-Júnior et al. (2021) also found no significant association between higher protein intake and global cognition in older adults. This result was similar in men and women, although some specific domains showed favorable associations.

Negative effects have also been described in specific contexts. A high-protein, low-carbohydrate diet did not improve global cognition in people with type 2 diabetes, and in one trial, psychomotor speed worsened compared with a conventional diet (Adams et al., 2025).

Food sources also affect the findings. While legumes, fish, and lean poultry were associated with better subjective cognitive function, processed meats were associated with greater decline. These differences may be related to the amount of advanced glycation end products, fats, and cooking methods, not just protein (Yeh et al., 2022).

Finally, Adams et al. (2025) note that the benefits observed in studies involving nuts cannot be attributed to their protein content alone, since these foods provide fiber, polyphenols, healthy fats, and micronutrients. The heterogeneity in doses, duration, protein sources, populations, and cognitive tests makes it impossible to establish a dose-response relationship or identify a high intake that improves cognition.

The benefits and drawbacks of the protein craze for health

The protein craze has increased awareness of the importance of preserving muscle mass, preventing sarcopenia, and meeting nutritional needs at different stages of life. It has also expanded the availability of convenient foods and supplements for athletes, older adults, and people with increased needs. Enriched products can make it easier to consume protein when appetite is low, time is limited, a calorie-restricted diet is being followed, or there is a specific clinical need. They can also help distribute intake throughout the day and after exercise (Clinthorne et al., 2026).

The problem arises when protein is treated as an automatic indicator of health. A cookie, bar, or dessert does not become nutritionally appropriate simply because it contains added protein. Some products still contain high amounts of sugar, fats, sweeteners, and other additives. The constant pursuit of more protein can displace foods rich in fiber, healthy fats, vitamins, minerals, and plant compounds. It can also encourage a less varied diet that is excessively focused on a single macronutrient (Kim et al., 2025).

For sedentary people who already meet their needs, additional intake through shakes, bars, or fortified products has not shown meaningful benefits for muscle mass, performance, or cognition. The usefulness of these products depends on individual circumstances, not just the amount of protein they provide.

Conclusions on protein intake for health professionals

Protein is essential, but its importance does not automatically make every fortified product healthy or justify recommending increased intake for the entire population. In addition to quantity, quality, source, and amino acid profile also matter. Not all proteins have the same composition or digestibility, or provide the same nutrients, so their effects may vary according to age, health, physical activity, and personal goals.

Therefore, a label stating “high protein” should not be interpreted as a guarantee of nutritional quality. Some fortified products are still ultra-processed and may contain high amounts of sugar, fats, sweeteners, or additives. It is also important to consider what type of protein they contain and which foods may be displaced when they are added to the diet.

The current “proteinization” of eating habits is too recent for us to know its long-term effects on the brain. We have studies on protein, aging, brain structure, and cognition, but we still do not know what will happen after decades of regular consumption of supplements and fortified products, especially among sedentary people who already meet their requirements. 

For now, the evidence suggests avoiding extreme messages. Neither “more protein is always better” nor “reducing protein extends life” applies to everyone. The most sensible approach is to eat a varied, balanced diet, prioritize high-quality sources, and adjust the amount and type of protein to individual needs. Not all sources or formulations are equally suitable for everyone, especially when allergies, intolerances, illnesses, or specific physiological needs are present. 

For this reason, decisions about increasing, reducing, or supplementing protein should be made in consultation with a nutrition or health professional and in accordance with the recommendations of leading nutrition organizations, which incorporate this nutrient into an overall dietary pattern rather than treating it as the absolute centerpiece of the diet.

References

• Adams, M. S., Mensink, R. P., & Joris, P. J. (2025). Effects of dietary proteins on cognitive performance and brain vascular function in adults: A systematic review of randomised controlled trials. Nutrition Research Reviews, 38, 450–464. https://doi.org/10.1017/S0954422424000271
• Clinthorne, J., Leidy, H. J., & Sollid, K. (2026). A modern take on protein nutrition meets evolving consumer perceptions. The Journal of Nutrition, 156(5), 101477. https://doi.org/10.1016/j.tjnut.2026.101477
• Coelho-Júnior, H. J., Calvani, R., Landi, F., Picca, A., & Marzetti, E. (2021). Protein intake and cognitive function in older adults: A systematic review and meta-analysis. Nutrition and Metabolic Insights, 14, 1–10. https://doi.org/10.1177/11786388211022373
• Cui, F., Li, H., Cao, Y., Wang, W., & Zhang, D. (2024). The association between dietary protein intake and sources and the rate of longitudinal changes in brain structure. Nutrients, 16(9), 1284. https://doi.org/10.3390/nu16091284
• Kim, S. Q., Spann, R. A., Hill, C. M., Berryman, C. E., Berthoud, H.-R., McDougal, D. H., He, Y., Münzberg, H., Yu, S., & Morrison, C. D. (2025). Protein-restricted diets and their impact on metabolic health and aging. Annual Review of Nutrition, 45(1), 269–297. https://doi.org/10.1146/annurev-nutr-121624-114918
• Knopf, B. A., & Lamming, D. W. (2026). The hallmarks of protein and amino acid restriction in aging and longevity. Cell Press Blue, 1, 100079. https://doi.org/10.1016/j.cpblue.2026.100079
• Nagao, K. (2024). Cognition and nutrition: The role of dietary protein and amino acids in cognitive health. Current Opinion in Clinical Nutrition & Metabolic Care, 27(1), 40–46. https://doi.org/10.1097/MCO.0000000000000987
• Yeh, T.-S., Yuan, C., Ascherio, A., Rosner, B. A., Blacker, D., & Willett, W. C. (2022). Long-term dietary protein intake and subjective cognitive decline in US men and women. The American Journal of Clinical Nutrition, 115(1), 199–210. https://doi.org/10.1093/ajcn/nqab236

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