Peptides get the hype. What about amino acids?

Hi there,

Everyone's obsessed with peptides right now. GLP-1 drugs, BPC-157, the whole alphabet soup. Peptides are chains of amino acids. This issue looks at some of those amino acids on their own.

The amino acid story in longevity is more interesting than I expected. A small GlyNAC trial improved several aging-related measures in older adults. Restricting some amino acids extended lifespan in mice. Neither finding proves that a supplement slows aging in people.

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.

A QUICK PRIMER: WHAT ARE AMINO ACIDS, ACTUALLY?

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.)

Amino acids link together to form peptides and proteins. The sequence and structure help determine what each molecule does.

When people get excited about peptide therapies, they're excited about particular molecules doing particular jobs. Individual amino acids can do more than help build those molecules.

Amino acids also send signals. Leucine activates mTOR, a pathway involved in growth and muscle building. Mouse research links altered mTOR signaling to aging, but it does not establish that an ordinary protein meal speeds human aging.

Growth signals help maintain muscle. Researchers also study how those signals relate to aging, which makes protein advice less simple than “more is better.”

Amino acids also appear in familiar products. Magnesium glycinate contains glycine, though that does not make it equivalent to a studied glycine dose. Taurine is an amino sulfonic acid; its longevity evidence is largely from animals. Creatine is an amino acid derivative with stronger evidence for muscle than for cognition.

The evidence hierarchy: from strong to speculative

I'm putting human trials first, then animal studies, then mechanisms that haven’t been tested in people. Those are very different reasons to consider a supplement.

GlyNAC: a promising small human trial

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

Kumar and colleagues randomized 24 older adults to GlyNAC or placebo for 16 weeks. Twelve young adults formed a separate comparison group. GlyNAC improved several metabolic and physical-function measures. The aging-hallmark analyses were exploratory; the trial did not test lifespan or disease prevention.

The trial used 100 mg/kg/day each of glycine and NAC. It was a monitored research protocol, not a dose to copy without clinical advice. An earlier eight-person pilot used 24 weeks of treatment and a 12-week withdrawal period.

These are small studies from one research group. The range of findings makes GlyNAC worth studying, but we need independent trials showing whether people stay healthier, not just whether markers improve.

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.

Glycine and methionine: a possible link

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.

Methionine restriction and calorie restriction are distinct research strategies. Their effects can overlap, but this evidence does not show that methionine explains all the benefits of calorie restriction.

Methionine restriction has no established human longevity protocol. Reducing protein without a clear nutrition plan can compromise muscle maintenance.

Glycine participates in methionine metabolism through GNMT, an enzyme that uses glycine to process methyl groups. That is a proposed explanation for some animal findings, not proof that supplemental glycine reproduces methionine restriction in humans.

The 2019 Interventions Testing Program study found a small lifespan benefit from an 8% glycine diet in male and female mice. The mechanism and a useful human equivalent remain uncertain.

Taurine: exciting, but read the fine print

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.

Later human studies complicated that story. NIH researchers reported in 2025 that taurine levels did not consistently decline with age across longitudinal human, monkey, and mouse data. That challenges taurine as an aging biomarker; it does not by itself test whether supplementation helps.

We still need human trials of longevity benefits and long-term safety. Finding taurine in an energy drink answers neither question.

I took taurine for 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 choosing what to drop, I start with the weakest evidence.

The BCAA paradox

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).

For older adults, adequate protein and resistance training have a stronger clinical basis than restricting BCAAs. Leucine-rich foods can help meet muscle needs, but isolated leucine is not a universal standard of care.

Muscle maintenance is a real human need. The lifespan result came from mice and does not show that leucine harms your grandmother.

There is no human trial showing that protein shakes accelerate aging at 30. At any age, match protein intake to activity, nutrition, muscle goals, and medical needs rather than using mTOR theory alone.

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.

The EAA hype: what the marketing gets right and wrong

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."

What do they add to food?

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."

BCAAs supply three of the nine essential amino acids. EAAs supply all nine. Both can affect muscle-protein synthesis, but adequate complete protein already supplies the full set.

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.

EAAs can help when appetite, food tolerance, or diet makes adequate protein hard to obtain. They are often unnecessary when food already meets your needs. Medical conditions can change that advice; supplements are not automatically harmless.

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

Emerging: creatine for brains, ergothioneine from mushrooms

Creatine has good evidence for muscle benefits. The brain research is much earlier.

Marshall and colleagues reviewed creatine and cognition in older adults. Only six studies met their criteria, and the evidence was sparse. Some findings favored memory or attention; broad cognitive benefit remains unproved. The paper appeared online in 2025 and in a 2026 issue.

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 a dietary antioxidant concentrated in mushrooms. A male-mouse lifespan study and an observational human cohort are interesting, but neither establishes that supplements prevent disease or extend human life.

Shiitake and king oyster mushrooms contain ergothioneine. Human supplement evidence is still early. In the meantime, they’re food.

THE CEO PROTOCOL: An amino acid protocol based on evidence, not vibes

There is no established rule that these supplements work better when separated from protein-heavy meals. Transporter biology alone cannot tell us whether timing changes health outcomes.

Choose timing that you can follow and tolerate. Food can help if a supplement causes stomach upset.

Start with adequate protein and established muscle benefits

GlyNAC: promising, but not a standard longevity protocol. The small trial used a much higher weight-based dose than glycine 3–5 g plus NAC 600–1,200 mg.

NAC can cause nausea and other stomach symptoms. A lower retail dose may be easier to tolerate, but it cannot claim the results of a different trial dose. Discuss use and medication interactions with your clinician.

The trial leaves long-term safety and health outcomes unanswered. It doesn’t establish a low-cost anti-aging regimen.

Creatine: 3-5g/day.

Muscle benefits have a stronger evidence base. Cognitive findings remain promising but sparse.

Creatine monohydrate powder mixes into water or a smoothie; capsules also work. For gummies, check the measured creatine content and product quality rather than assuming the stated dose survived manufacturing.

Higher doses can change brain creatine in some small studies, but a measured increase does not prove better cognition. An optimal brain-health dose has not been established.

Research under sleep deprivation is interesting, but it does not establish a treatment for chronic poor sleep or concussion.

Guanidinoacetic acid, a creatine precursor, has appeared in small brain-creatine studies. That is early research, not a reason to add it to a routine protocol.

Creatine 3–5 g/day is a common maintenance dose for muscle goals. Do not raise the dose to treat a head injury or sleep problem without clinical advice; brain-health dosing remains uncertain.

For routine use, taking creatine consistently matters more than the time of day. If you notice sleep or stomach problems, adjust timing or discuss stopping it with your clinician.

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

Early evidence: optional, with clear limits

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.

Taurine has animal and human physiology data, but no established human longevity benefit. If cost or supplement count is a constraint, this is the first one I'd drop.

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

No timing schedule has shown that glycine works better for longevity. If you choose it, consider tolerance and total intake rather than a strict meal gap.

Count glycine from all products. Magnesium glycinate is not equivalent to a tested standalone glycine dose, and its glycine content does not establish a sleep benefit.

Ergothioneine: mushrooms are a dietary source. No supplement dose has established a human longevity benefit.

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.

Tier 3: Intriguing but premature

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 remains an animal-research strategy. One or two low-protein days per week have not been shown to reproduce its lifespan effects in humans.

Isoleucine restriction: Too early. Mice-only, mechanistically interesting, but no clear human protocol exists.

How needs change with age

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: meet protein needs for your activity and goals. Neither routine glycine nor low-protein days have shown a human longevity benefit. Avoid treating the minimum protein allowance as an ideal target for every active person.

Ages 50–65: keep muscle strength and protein adequacy in view. GlyNAC remains an optional, early-evidence choice rather than an age-based requirement.

Ages 65–75: many older adults benefit from roughly 1.0–1.2 g/kg/day of protein, with higher needs in some settings. Leucine-rich meals matter; expert guidance often discusses about 2.5–2.8 g per meal. Kidney disease and other conditions can change the plan. GlyNAC is not a standard recommendation.

Ages 75+: prioritize adequate food, protein, and strength training as able. Illness, frailty, and kidney function can change protein targets. EAAs may help when intake is poor; there is no evidence-based requirement for a full longevity supplement stack.

These are broad starting points. I often recommend more protein for patients working on body recomposition. Your goals, training, appetite, and health matter more than an age bracket; work with your physician, dietitian, or nutritionist on the plan.

A final word: what to actually do if building muscle is the goal

For muscle building or body recomposition, adequate protein and training come first. Animal longevity experiments do not supply a separate validated human protein target.

The hierarchy, from most to least effective:

1. Whole food protein: leucine-rich sources (animal protein, legumes with complementary amino acids) distributed across 3-4 meals, aiming for 30-40g per meal to clear the leucine threshold for maximal muscle protein synthesis.

2. Quality protein powder: whey isolate is the benchmark; it's leucine-rich, complete, and the most studied. Casein before sleep has some data for overnight recovery.

3. EAA supplements: useful if you want an amino acid hit without a full protein meal, particularly around training.

4. BCAAs: the bottom of the list. If you're already hitting adequate protein, BCAAs are redundant. Leucine from your protein meal already did the signaling. You're just adding cost and oxidation load.

AMINO ACID KEY TAKEAWAYS

• GlyNAC merits study; small trials of markers and function do not prove longer or healthier human life.

• BCAA restriction has mouse lifespan data. Do not infer that ordinary protein intake accelerates human aging.

• Taurine, glycine, and ergothioneine have no established human longevity protocol.

• Protein needs depend on activity, age, muscle goals, illness, and kidney function.

• For muscle goals, start with food and training; supplements can fill a real gap.

LONGEVITY QUICK HITS

• 🫀 New lipid guidance: The 2026 ACC/AHA guideline recommends Lp(a) testing at least once and selective ApoB testing. PREVENT risk estimates cover adults 30–79; this is not universal ApoB screening or statins at 30.

• 📊 CGM and mortality: A nationwide type 1 diabetes cohort linked CGM use to fewer complications and deaths. The study was observational and cannot prove that CGM caused the difference; it does not apply to people without diabetes.

• 💊 Oral PCSK9 inhibition: In the 2,909-person CORALreef Lipids trial in high-risk adults, enlicitide produced an adjusted LDL-C reduction of 55.8 percentage points versus placebo at 24 weeks. The trial tested cholesterol lowering, not whether it prevented heart attacks.

• Different organs, different age estimates. An April 2026 UK Biobank imaging study estimated age in the brain, heart, kidneys, liver, pancreas, spleen and retina. Some age gaps tracked disease and mortality. We don’t yet know whether using these scores to guide care helps patients.

• Gene therapy improved hearing in a small, specific trial. A Nature Medicine single-arm trial published in July 2025 reported hearing improvement in ten people with OTOF-related inherited deafness over 6–12 months. The study had no control group, and longer follow-up is needed to establish lasting benefit and safety.

FROM THE LONGEVITY SHOW

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

We spend so much on exotic interventions. Meanwhile, a small human trial of two familiar supplements produced findings worth following. Low cost is appealing; it does not make the evidence stronger.

GlyNAC isn't glamorous. The small human trial got my attention; now I want to see it replicated.

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, Curator

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Events listed when this issue was published

👱🏻‍♀️👩🏻‍🦰👩🏻👧🏽👧🏾 Livelong Women's Health Summit, April 17-18, 2026, SF, CA. Delighted to join 50 other thought leaders in speaking on women's longevity! (Code HILLARY50 for $50 off)
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, May 26-27, Mosesian Center for the Arts, Greater Boston. I'll be on the clinician panel discussing how aging research translates into real interventions.

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