As we navigate the complexities of ageing, it becomes increasingly evident that nutrition plays a pivotal role in maintaining cognitive function and overall brain health. Among the myriad nutrients that contribute to our wellbeing, protein stands out as a critical component that can significantly influence the rate of brain ageing. In this article, we will explore the essential role of protein and amino acids in cognitive function, the potential risks associated with protein malnutrition, and practical dietary recommendations to enhance longevity and brain health. From supporting hormone function to ensuring oxygen delivery, balancing blood sugar, and even building brain tissues, protein plays a critical role in maintaining cognitive health and overall well-being. Plus, it helps reduce hunger and build brain tissues, making it an indispensable part of a brain-healthy diet.

Understanding the Role of Protein in Brain Health

Proteins are composed of amino acids, which are the building blocks that help our bodies function optimally. Notably, certain amino acids are crucial for the synthesis of neurotransmitters chemicals that transmit signals in the brain. Amino acids such as tryptophan, tyrosine, histidine, and arginine are vital for the production of serotonin, dopamine, and norepinephrine, all of which play roles in mood regulation, memory, and cognitive performance.

Emerging evidence suggests that protein malnutrition may be a risk factor for conditions such as senile dementia. While the precise relationship between protein intake and cognitive decline remains to be fully elucidated, studies indicate that inadequate consumption of specific amino acids can adversely affect brain function. For example, tryptophan depletion has been linked to increased feelings of depression and aggression, highlighting the importance of maintaining optimal amino acid levels for cognitive wellbeing.

The prevalence of dementia is rising globally, making initiatives aimed at preventing it essential for creating a society that accommodates individuals with dementia (1). As there is currently no ideal medication for dementia prevention, developing easily accessible preventive strategies for everyday life is crucial. Dementia is linked to aging and the buildup of various risk and protective factors throughout a person’s life. Cognitive decline can emerge as a social issue even in healthy individuals prior to a dementia diagnosis. To postpone the onset of dementia or mitigate cognitive decline, it is important to focus on middle-aged individuals and younger seniors.

The Impact of Amino Acids on Cognitive Function

Research has shown that the ingestion of essential amino acids—specifically leucine, phenylalanine, and lysine—can positively affect cognitive and psychosocial functions. A daily intake of these amino acids, in conjunction with isoleucine, histidine, valine, and tryptophan, has demonstrated improvements in attention and cognitive flexibility. In particular, a daily dose of 6 grams of these essential amino acids has been associated with enhanced mental performance.

During periods of undernutrition or high stress, the brain’s requirements for these amino acids may become even more pronounced. Studies involving soldiers under energy-deficient conditions have revealed that reductions in tryptophan correlate with impaired cognitive performance. This indicates that maintaining adequate levels of specific amino acids is essential for optimal brain function, particularly in stressful situations.

Branched-chain amino acids (BCAAs) are recognized for their neuroprotective properties following traumatic brain injury (TBI). Although there are significant clinical benefits observed in severe TBI patients treated with BCAAs, this treatment remains largely overlooked. Arginine, a crucial component of collagen, aids in minimizing fine lines and wrinkles and is also known for its wound-healing properties, making it beneficial for those with damaged skin.

The brain requires over 20 amino acids to maintain protein and peptide synthesis. Four of these (glutamate, aspartate, glycine, and GABA) function as neurotransmitters, while three others (tryptophan, histidine, and tyrosine) serve as precursors to neurotransmitters, and two derivatives of thyronine (T3 and T4) act as hormones. As individuals age, protein synthesis in the body diminishes, and this decline is particularly pronounced in the brain, where amino acid metabolism shows significant regional variability.

Aging affects the metabolites produced from l-tyrosine (which form catecholamines), l-tryptophan (which produces serotonin, melatonin, and kynurenic acid), and l-arginine (which generates nitric oxide). Additionally, the metabolism of amino acids is altered, and levels of glutamate receptors, including N-methyl-d-aspartate (NMDA), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), kainate subreceptors, and nitric oxide synthase, are modified. The levels of d-serine, an essential amino acid that regulates NMDA receptor activity, decrease with age. The mechanistic target of rapamycin (mTOR) plays a role in integrating various environmental and intracellular signals and responds to l-leucine and l-arginine, with mTOR inhibition associated with increased lifespan. Furthermore, gut microbiota affects brain function by influencing amino acid metabolism in a manner that varies with age.

Dietary Recommendations for Optimal Protein Intake

To support cognitive health and promote longevity, it is crucial to ensure a balanced intake of protein from a variety of sources. Here are some dietary recommendations:

1. Incorporate High-Quality Protein Sources: Include lean meats, fish, eggs, dairy products, legumes, and nuts in your diet to provide a rich array of essential amino acids.
2. Consider Plant-Based Proteins: For those following a vegetarian or vegan diet, combining different plant-based proteins (e.g., beans ) can ensure a complete amino acid profile.
3. Supplement with Amino Acids: For older adults or those at risk of cognitive decline, consider amino acid supplements, particularly those rich in tryptophan and tyrosine, to support brain health.
4. Probiotic Supplementation: A healthy gut microbiota has been linked to improved cognitive function. Incorporating probiotics, such as Lactobacillus and Bifidobacterium strains, can enhance gut health and, by extension, support brain function.
5. Stay Hydrated: Adequate hydration is essential for nutrient absorption and overall cognitive performance.

My thoughts

As a clinical dietitian, I believe that the journey toward longevity extends beyond merely counting calories or macronutrients. It is about creating a balanced, nutrient-rich environment that nurtures both the body and mind. Adequate protein intake, alongside a focus on essential amino acids and gut health, can play a significant role in delaying cognitive decline and promoting overall wellbeing. By prioritising these dietary strategies, we can help pave the way for a healthier, more vibrant future.