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Everyone's obsessed with peptides right now. GLP-1 agonists, BPC-157, the whole alphabet soup. And yet, amino acids are basically peptides' younger, scrappier siblings. Peptides are chains of amino acids. That's it. You're already hearing about the chains. This issue is about what happens when you zoom in on the individual links.

The amino acid story in longevity is far more interesting and important than I expected. You've got one amino acid combo that reversed seven aging hallmarks in a single human trial. Another gym bros take that is actually speeding up their aging. One that extends lifespan in mice by mimicking starvation, without the starvation part. And the cheapest option on the list costs about 70 cents a day.

Some claims about amino acids online check out. Some really don't. Here's the evidence, ranked by quality, with a framework for what to actually do about it.

You probably remember amino acids from high school biology. "Building blocks of protein."

True, but here's the more interesting version.

Your body uses a combination of 20 amino acids to build every protein it makes. Nine of them are "essential," meaning your body can't synthesize them. You have to eat them to have them.

The other eleven, your body can make on its own, which is why they're called "non-essential." (Terrible name. They're not unimportant. Your body just figured out how to DIY them.)

Think of it like LEGO. Amino acids are individual bricks. So where do the ever-popular peptides come in? Peptides are small structures made from a few bricks, like pre-built LEGO buildings. Proteins are the elaborate castle on the box cover.

When people get excited about peptide therapies, they're excited about specific small structures doing specific things. But some of the individual bricks, on their own, turn out to be surprisingly powerful.

In the longevity world, amino acids don't just build things. Just like peptides, they also signal. Leucine, for example, activates mTOR, a master growth switch inside your cells. mTOR activation is great when you’re trying to build muscle. It's a lot less great when it stays chronically elevated and accelerates cellular aging.

Same molecule, opposite problem depending on when and how much.

That tension between growth and degeneration is the entire story of amino acids in longevity science. And it's why the "take more protein" advice that's everywhere right now is both right and incomplete.

Also, amino acids show up in places you might not expect. Magnesium glycinate, the sleep supplement half of the longevity world seems to be taking? That's magnesium bound to glycine. The glycine isn't just a carrier molecule. It's doing things on its own. Taurine, the ingredient in energy drinks? It's technically an amino sulfonic acid, and it might extend lifespan. Creatine, which bodybuilders have used since the 90s? An amino acid derivative that turns out to be good for your brain, not just your biceps.

The amino acid world is bigger than most people realize. Let's get into what the evidence actually says.

Not all amino acid research is created equal. I'm ranking these by evidence quality: human RCTs at the top, animal studies in the middle, mechanistic data at the bottom. The goal is to get clarity beyond the hype.

If I could only tell you about one amino acid finding in aging research, this would be it.

Kumar et al. (2023) ran a placebo-controlled human RCT (n=36) on GlyNAC supplementation, which is just glycine plus N-acetylcysteine. The results? GlyNAC corrected 7 aging hallmarks — including mitochondrial dysfunction, oxidative stress, inflammation, insulin resistance, endothelial dysfunction, genomic damage, and body composition — compared to no change in placebo.

The protocol: Glycine 3-5g/day plus NAC 600-1200mg/day for 16-24 weeks. Total cost: $20-30/month. An earlier open-label pilot (2021, n=8) by the same Sekhar group at BCM had showed similar improvements in glutathione, cognition, and muscle strength over 36 weeks.

Now, caveats: this is one research group with small sample sizes. We need replication from independent labs. But the breadth of effects is unlike anything else in the amino acid literature. It's not one biomarker moving in the right direction. It's the biological equivalent of your whole house getting cleaned at once.

I've been taking GlyNAC myself for the past several months. No dramatic subjective changes, which honestly is what you'd expect. You don't feel your mitochondria improving. I take it based on evidence, plus it’s an excuse to get a full glass of water each morning.

This is one of my favorite mechanisms in longevity biology because it's so elegant (and non-obvious).

Methionine restriction is one of the most replicated life-extension findings in animal research: 30-40% lifespan extension in rodents, replicated across multiple labs and species.

Where we credit caloric restriction for lifespan benefits, we should probably be crediting methionine restriction instead.

The problem is that achieving meaningful methionine restriction in humans means eliminating essentially all animal protein. Not practical for most people, nor desirable considering other health effects (sarcopenia).

Glycine offers a back door. When you supplement glycine, it upregulates an enzyme called GNMT (glycine N-methyltransferase) that diverts methionine away from growth signaling pathways. You’re not restricting methionine intake, but rather redirecting where it goes. It’s like diverting traffic instead of closing the road.

This is likely why glycine supplementation extended median lifespan 4-6% in the NIA Interventions Testing Program (Miller et al., Aging Cell 2019) — in both male and female mice, which is notable because most longevity interventions show sex-specific effects.

Singh et al. (Science, 2023) showed taurine declines with age in mice, worms, and monkeys, and supplementation extended lifespan and healthspan in mice and worms. The human data in the paper showed taurine also declines with age in people — which is what got everyone in longevity excited.

Then Marcangeli et al. (Aging Cell, 2025) measured taurine levels in humans across age groups and found no association between taurine levels and aging markers. None. The NIH NIA echoed this conclusion that same year — taurine is unlikely to be a reliable aging biomarker in humans.

The animal data is interesting, plus the safety profile is excellent (you've been drinking taurine in Red Bull since college). But the gap between mouse longevity and human aging is glaring.

I took taurine for about some time before deprioritizing it. Not because of safety concerns, but because the human data just isn't there yet. Supplement fatigue is real. When you're choosing what to drop, you drop the ones with the weakest evidence.

This one is important for the fitness community.

Richardson et al. (Nature Aging, 2021) showed that lifelong BCAA restriction (leucine, isoleucine, and valine — the branched-chain amino acids in your protein shake) significantly extended lifespan in male mice and reduced frailty.

Side note: the effect was sex-specific. Male mice benefited, female mice did not see the same lifespan extension (a recurring story in longevity research).

But the problem is that leucine (a BCAA) supplementation is the standard-of-care recommendation for sarcopenia prevention in older adults.

The same amino acid that might accelerate aging is also the one preventing your grandmother from losing muscle mass.

It's a genuine paradox that makes a lot of sense. At 30, chronically elevated mTOR from protein shakes and BCAA supplements may be paying a long-term cost. At 75, the immediate risk of muscle loss outweighs the theoretical longevity cost of mTOR activation.

Different decades, different math.

For practical purposes, BCAA restriction as a longevity strategy is real in animals but practically unimplementable in humans outside of controlled settings. You'd have to restructure your entire diet. The more actionable version is to think about protein quality and timing rather than trying to restrict specific amino acids.

Essential amino acid supplements are everywhere right now, and the marketing is disproportionately aimed at women.

The pitch usually sounds like: fewer calories than protein powder, faster absorption, no carbs or fat, supports lean muscle without "bulking." Products are often pastel-colored and feature words like "toning," "recovery," and "hormonal support."

Here's the actual science.

Your body can't synthesize nine amino acids — they're called essential because you have to eat them. EAA supplements deliver exactly those nine in free form, bypassing the digestion step protein requires.

The faster absorption claim is technically true, but for most people eating adequate protein, this doesn't translate into a meaningful advantage.

The women's targeting isn't entirely fabricated. There are real sex-based differences in amino acid metabolism: women tend to oxidize less leucine at rest and may have a slightly different leucine threshold for triggering muscle protein synthesis.

But the practical implication of this finding is "women may need to be more deliberate about leucine-rich protein sources" — not "buy this new supplement."

Also, what is the difference between EAA and BCAA supplements? BCAAs are only three of the nine essentials, so they can trigger muscle protein synthesis signaling without supplying all the building blocks to finish the job, so EAAs are slightly more complete.

But EAA supplements do not beat a quality protein source that contains all nine essentials plus some, and costs less. Whey isolate, eggs, and most animal proteins already deliver everything EAA supplements do, plus the non-essential amino acids that do their own work.

When do EAA supplements make sense? If you can't stomach protein powder, want a very low-calorie amino acid hit around a workout, or are eating a plant-based diet with inconsistent protein coverage. They're not harmful. They're just mostly unnecessary if your diet is already doing its job.

(Plus, subjective opinion perhaps, but they do not taste great 🤢.)

Creatine needs no introduction. And it does have legitimate, supported benefits for muscle. For the brain, there’s some new evidence, although that is much earlier.

A 2026 systematic review in Nutrition Reviews (Marshall et al.) found cognitive benefits from creatine supplementation in older adults across memory, attention, and processing speed — now supported at the systematic-review level. Muscle and strength benefits have been established for longer. Note: a methodological critique of this review was published in late 2025 — the signal is real but effect sizes remain modest.

I should mention: creatine and I did not get along. It worsened my insomnia, specifically early morning awakening, and I suspect that's because I don't have an energy problem in my brain. I have the opposite, having genetically defined low sleep pressure. But I still recommend creatine to most of my patients because the data is genuinely strong, and my experience is an N of 1.

Ergothioneine is another animo acid with emerging evidence — a dietary antioxidant concentrated in mushrooms. Katsube et al. (GeroScience, 2024) showed ergothioneine extends median lifespan and promotes healthy aging in male mice. Cheah & Halliwell have published extensively on ergothioneine’s antioxidant and neuroprotective properties, and human observational data links higher ergothioneine levels to reduced cardiovascular mortality (Smith et al., Heart, 2020).

Eat shiitake or king oyster mushrooms to get egothioneine through your diet. It’s still early days for supplementation in humans — not yet a strong human RCT.

OK, now let’s talk about how to use all this evidence about amino acid supplementation in real life.

First rule: amino acid supplements generally work best taken separately from protein-heavy meals. Why? Because amino acids compete for the same transporters in your gut.

When you take glycine alongside a steak, the glycine is competing with 20 other amino acids for absorption. It’s like one lonely voice trying to shout over a barbershop quartet. Take it between meals or before bed, and it gets VIP access.

This isn't absolute. I’ll cover which amino acids do not require separation from food and why below.

GlyNAC: Glycine 3-5g/day plus NAC 600-1200mg/day.

This is OK to take with meals. I know I just said amino acids absorb better on an empty stomach, and that's true for glycine and NAC, but NAC is a sulfur compound that irritates gastric mucosa. It can cause real nausea without food. The Kumar trials dosed with meals and got their positive results anyways, so it seems absorption at that higher dose is fine.

This is the only amino acid intervention backed by a human aging RCT showing reversal of seven aging hallmarks. Cost: $20-30/month.

Creatine: 3-5g/day.

Muscle benefits are well-established. Cognitive evidence just reached systematic-review level in 2026 — real signal, modest effect sizes.

The powder is easy dissolved in water/a smoothie, and capsules work as well (gummies require closer inspection, since the heat required to create gummies often destroys creatine).

But what about higher doses for the brain? The creatine transporter at the blood-brain barrier (CRT1/SLC6A8) operates near saturation, so the brain is genuinely harder to load than muscle. MRS imaging studies show 10g/day increases frontal lobe phosphocreatine roughly double what 4-5g achieves. At 20g/day, results are inconsistent — high variability between subjects.

The real question is whether that extra 5-10% brain creatine improves cognition. In healthy, rested adults: not convincingly. Under metabolic stress (sleep deprivation, jet lag, post-concussion), the case is stronger.

One interesting development is the finding that guanidinoacetic acid (GAA), a creatine precursor, raised brain creatine by 16% at just 3g/day in a crossover trial — it can use transport pathways that creatine itself can’t access.

My take: 5g/day is sufficient if you’re sleeping well. If you’re chronically sleep-deprived or recovering from a head injury, 10g may be worth trying. Don’t bother with loading phases or 20g — your muscles have a fixed storage ceiling, and the brain data at that dose is a coin flip.

Regardless of dose, the 'take creatine in the morning' advice that's everywhere online has no mechanistic basis. Creatine works by saturating your intracellular phosphocreatine pool over weeks, not by creating an acute spike. That pool has a half-life of days. Whether today's dose hits at 7am or 10pm changes nothing about a reservoir that turns over across days.

Take it whenever you'll actually remember. With food reduces GI upset. Cost: ~$15/month.

Taurine: 1-3g/day.

Take any time, with or without food. Taurine gets a free pass on timing around food because it uses its own dedicated transporter (TauT/SLC6A6) that other amino acids don't compete with.

Strong animal longevity data, excellent human safety profile, awaiting a human aging RCT. Marcangeli et al. (Aging Cell, 2025) recently showed no lifespan extension in a well-powered mouse study, which tempers some of the earlier excitement from Singh et al. If cost or supplement count is a constraint, this is the first one I'd drop from the stack. But the safety profile is excellent.

Glycine (standalone, beyond GlyNAC dose): Up to 5g/day total.

Best taken 30 minutes before a meal or 2+ hours after one for optimal absorption. Glycine uses shared amino acid transporters (SLC family), so a protein-heavy meal floods those transporters with competing amino acids.

You can take extra glycine even if you’re taking magnesium glycinate for sleep (the glycine in mag glycinate is doing double duty as an inhibitory neurotransmitter that promotes sleep onset).

Ergothioneine: Eat shiitake or king oyster mushrooms (5-10mg per serving). If supplementing: 5-25mg/day.

With or without food, it doesn't matter much. Ergothioneine absorbs via OCTN1, a dedicated transporter that isn't bottlenecked by dietary amino acid competition. Or just eat more mushrooms.

BCAA restriction: Animal data is compelling, but practically impossible to implement at the threshold required. Focus instead on protein quality: varied sources, leucine-adequate meals, less processed protein.

Methionine restriction: Not practical as a standalone strategy. Periodic protein cycling (1-2 lower-protein days per week) may capture partial benefit via the glycine pathway. Worth experimenting with.

Isoleucine restriction: Too early. Mice-only, mechanistically interesting, but no clear human protocol exists. File under "watch this space."

Protein and amino acid needs shift substantially across the lifespan. What's right at 30 isn't right at 70, and getting this wrong in either direction has real consequences.

Ages 20-50: Moderate protein (0.8-1.0g/kg). Add glycine supplementation. Try periodic protein cycling 1-2x/week for longevity signaling benefits. This is the window where mTOR restraint matters most.

Ages 50-65: Gradually increase protein toward 1.0-1.2g/kg. Maintain glycine. Consider GlyNAC if budget allows. The transition period: muscle preservation starts becoming more important than growth pathway suppression.

Ages 65-75: 1.2g/kg protein minimum. Leucine-enriched meals (5-10g leucine per meal) for anabolic signaling. GlyNAC becomes a strong recommendation. The math has shifted: losing muscle at this age has immediate, measurable consequences.

Ages 75+: 1.2-1.5g/kg protein. Consider EAA supplementation if whole-food intake is inconsistent. Full Tier 1 stack strongly recommended. At this stage, the risk of undernutrition far outweighs theoretical concerns about mTOR activation.

Notably, this is a very broad overall strategy that is a starting point. In most of my patients, who have many health goals beyond simply lifespan, I actually do not follow these targets whatsoever. Commonly, for example, I will recommend much higher protein ranges because many patients are attempting body recomposition. Work with your physician, dietician, or nutritionist to craft an evidence-based protocol individualized for your health goals.

Everything above is calibrated for longevity. If your primary goal is muscle building or body recomposition, the calculus shifts — but not as dramatically as supplement companies want you to believe.

The hierarchy, from most to least effective:

An oldie but a goodie — a quick overview of peptides and hormones!

We spend so much time and money on exotic interventions, designer peptides that cost $300/month, stem cell therapies that cost $10,000 a session, and meanwhile the most compelling human RCT in aging biology involves two supplements that cost less than a daily coffee.

GlyNAC isn't sexy. It doesn't have a cool brand name. Nobody's building a DTC company around it. Maybe that's why it stays under the radar. The things that work aren't always the things that sell.

I keep thinking about what else we might be overlooking because it's too cheap, too simple, too boring to generate buzz. Probably a lot.

Keep learning,

Hillary Lin, MD

Co-Founder & CEO, CareCore

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