Amino Acids

Amino acids and aging: building blocks of longevity

Amino acids are the 20 molecular units that make up every protein in the human body. Nine of them are "essential," meaning we can't produce them ourselves and must get them from food. Beyond building muscle and tissue, amino acids act as raw material for neurotransmitters, hormones, immune cells, and the signaling pathways that regulate how we age. Getting the right amino acids in the right amounts becomes more important with each passing decade.

The nine essential amino acids

The essential amino acids (EAAs) are leucine, isoleucine, valine, methionine, threonine, tryptophan, histidine, phenylalanine, and lysine. Of these, leucine, isoleucine, and valine are the branched-chain amino acids (BCAAs), named for their chemical structure. Complete protein sources like meat, fish, eggs, and dairy contain all nine in adequate proportions. Plant-based eaters can achieve full coverage by combining legumes, grains, and seeds throughout the day, though individual plant foods often lack one or more EAAs ^[1].

Why amino acids matter more as you age

After age 40, the body gradually loses muscle mass at a rate of roughly 3-8% per decade, a process called sarcopenia. One reason is "anabolic resistance": aging muscles become less responsive to the protein synthesis signal from amino acids, particularly leucine. Overcoming this requires both higher protein intake (1.0-1.2 g/kg/day for adults over 65, versus the standard 0.8 g/kg) and a threshold of about 30-35 g of protein per meal ^[2]. A 2021 randomized controlled trial found that daily EAA supplementation improved grip strength, walking distance, and lean mass in older adults with low physical functioning ^[3].

Leucine and the mTOR pathway

Leucine is the strongest dietary activator of mTOR (mechanistic target of rapamycin), the master switch for muscle protein synthesis. This makes leucine-rich foods and EAA supplements particularly effective for preserving muscle after exercise. But here's where longevity science gets complicated: chronic mTOR activation is also linked to accelerated aging and reduced autophagy. The current evidence suggests that pulsed mTOR activation through protein-rich meals timed around exercise, followed by periods of lower amino acid intake or fasting, may offer the best balance between muscle maintenance and longevity ^[4].

Amino acids beyond muscle: neurotransmitters, sleep, and immunity

Tryptophan is the precursor to serotonin and melatonin, directly influencing mood, sleep quality, and circadian rhythm. Brain serotonin levels decline with age, and dietary tryptophan can partially counteract this ^[5]. Histidine gives rise to histamine, which regulates immune responses. Methionine feeds into the methylation cycle, affecting DNA repair and gene expression. Glycine, a conditionally essential amino acid, is gaining attention in longevity research through GlyNAC (glycine + N-acetylcysteine) supplementation, which in a 2023 randomized clinical trial reversed multiple hallmarks of aging in older adults, including mitochondrial dysfunction, oxidative stress, and cellular senescence ^[6].

The amino acid restriction paradox

Interestingly, restricting certain amino acids can also extend lifespan. Reducing isoleucine intake by two-thirds increased median lifespan by 33% in male mice in a 2023 study ^[7]. Methionine restriction has shown similar longevity benefits across species, likely by reducing mTOR and IGF-1 signaling. BCAA restriction started at midlife led to a 30% lifespan increase in male mice ^[8]. These findings don't contradict the need for adequate protein. They suggest that the specific ratio and timing of amino acid intake matters: enough leucine around exercise to build muscle, but not constant excess that keeps mTOR permanently activated.

Practical amino acid strategy for healthy aging

For most people, the priority is getting enough high-quality protein distributed across meals. Aim for 1.0-1.6 g/kg/day depending on activity level and age, with 30+ grams per meal. If you train regularly, consuming EAAs or a leucine-rich protein source within two hours of resistance exercise maximizes the anabolic response. EAA supplements can be useful for older adults who struggle to eat enough protein, those on restricted diets, or people who want to stimulate muscle synthesis with fewer total calories. Whole-food sources remain the foundation, as they provide the full spectrum of amino acids plus co-factors needed for absorption.