Two amino acids — glycine and N-acetylcysteine — combined and dosed correctly produced striking improvements in glutathione levels, mitochondrial function, insulin resistance, and walking speed in older adults at Baylor. Here's the protocol and how to do it.
In 2021, a research team at Baylor College of Medicine published a small but striking randomized trial of an intervention they called GlyNAC — a combination of glycine and N-acetylcysteine (NAC) — in older adults. The 16-week trial showed substantial improvements in glutathione synthesis, mitochondrial function, insulin resistance, body composition, walking speed, cognition, and several inflammatory markers. The effect size was unusual for a nutritional intervention, particularly for the functional outcomes in older adults.
The GlyNAC protocol has since gained traction in longevity practice, both as a standalone intervention and as a component of broader stacks. This article explains what GlyNAC is, what the Baylor trials showed, the precise dosing protocol used, the supplement options, and how to integrate it.
Glutathione is the body's most abundant intracellular antioxidant, critical for detoxification, cellular redox balance, and mitochondrial function. Glutathione is synthesized from three amino acids: glutamate, cysteine, and glycine. Cysteine availability is typically the rate-limiting step in younger adults; glycine becomes increasingly limiting in older adults.
Older adults have substantially lower glutathione levels and reduced glutathione synthesis capacity. The Baylor team hypothesized that providing both rate-limiting precursors — cysteine (as NAC) and glycine — would restore glutathione synthesis to younger levels.
NAC alone provides cysteine but does not address the glycine bottleneck. Glycine alone provides glycine but doesn't address potential cysteine limitations. Combined, the two amino acids correct both bottlenecks simultaneously.
Pilot study (2018): 8 older adults received 1.33 mmol/kg/day glycine + 0.81 mmol/kg/day NAC for 14 days. Plasma glutathione increased substantially. Mitochondrial fatty acid oxidation improved. Inflammatory markers decreased.
Main RCT (2021): 24 older adults randomized to GlyNAC vs placebo for 16 weeks. Active dose: 1.33 mmol/kg/day glycine (~100 mg/kg) + 0.81 mmol/kg/day NAC (~133 mg/kg). Active group showed:
These are unusually strong functional improvements for a nutritional intervention. The trial was small (n=24), open to placebo bias despite blinding (subjects could potentially detect the supplement taste), and short-term (16 weeks). Larger and longer trials are needed.
The trial doses, translated to weight-based per-day amounts for a 70 kg (155 lb) adult:
These are large doses by typical supplementation standards. They were divided into 2–3 servings per day, taken with meals.
For a 90 kg (200 lb) adult:
These doses sound enormous compared to typical supplementation, but glycine and NAC are inexpensive amino acids with extensive safety data at much higher doses (NAC has been used at 70+ g IV in acetaminophen poisoning).
Most users implementing the Baylor protocol divide doses across 2–3 administrations:
Morning: 3 g glycine + 4 g NAC with breakfast
Midday: 2 g glycine + 3 g NAC with lunch
Evening: 2 g glycine + 2 g NAC with dinner
A 90-day supply at full Baylor dose costs approximately $40–80 from bulk powder.
Capsules are more expensive (~$80–150 for 90-day supply) but more practical for travel.
A few brands now offer pre-formulated GlyNAC (Nuchido TIME+, Nestlé Healthy Aging GlyNAC). These are convenient but typically dose well below Baylor protocol levels. If you choose a pre-formulated product, verify that doses match the published trial.
Both glycine and NAC have extensive safety data. Side effects at the Baylor protocol dose:
Long-term safety at the Baylor dose has not been studied beyond 16 weeks. Most practitioners cycle 12 weeks on, 4 weeks off, or maintain a lower maintenance dose after initial protocol completion.
GlyNAC pairs particularly well with:
It overlaps mechanistically with senolytic and glutathione-supporting interventions; users implementing both should monitor for redundancy.
For more on the broader amino acid and protein supplementation landscape, see Protein for Longevity: How Much, What Source, When and The Aging Antioxidant System.
Is GlyNAC safe for younger adults?
Probably yes, but the evidence base is in older adults with documented glutathione deficiency. Younger adults with normal glutathione synthesis may not see benefit.
Can I just take more NAC?
The whole point of GlyNAC is the combination. NAC alone doesn't address the glycine bottleneck in older adults. Both amino acids matter.
Will my doctor know about GlyNAC?
Most general practitioners are unfamiliar with the Baylor work. Print the published papers and bring them.
Can I get the same benefit from food?
The doses required are too high to achieve from food alone. A 7 g daily glycine intake from food would require, e.g., very large amounts of bone broth or skin-on poultry. Supplementation is the practical route.