The Forgotten Amino Acid in Slow-Cooked Foods

A building block of protein, glycine was once obtained naturally from a diet high in slow-cooked connective tissues, bone broth, and marrow.

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The expensive protein powders on the market offer an amino acid that your great-grandmother got for free—from the parts of the animal nobody wanted.

Bone broth simmered for hours, fall-off-the-bone lamb shank, rich slow-cooked meats, buttery bone marrow spread onto toast—these foods weren’t delicacies; they were once regular meals. Without knowing it, generations of home cooks were providing an overlooked nutrient—glycine.

Glycine is the body’s smallest amino acid, but it plays a very important role in repair and inflammation. During periods of stress or increased physical strain, the body needs even more.

What Glycine Does

Glycine makes up roughly one-third of all collagen, and it is structurally essential for skin, joints, tendons, ligaments, and fascia.

“It’s far more than just a structural amino acid,” Jodi Duval, a naturopathic physician and owner of Revital Health, told The Epoch Times.

Glycine is needed for some of the body’s most important repair and protective processes. It is a precursor to glutathione, often called the body’s master antioxidant, which defends cells against oxidative damage.

It also helps maintain the integrity of the intestinal lining, which is important for immune function, and acts as a calming neurotransmitter, helping support sleep quality, nervous system regulation, and recovery. The amino acid becomes even more important with age because it is heavily involved in muscle preservation, sleep architecture, connective tissue integrity, and healthy aging pathways, Duval said.

An Anti-Inflammatory

During periods of intense exercise, poor sleep, chronic stress, or inflammatory illness, demand for glycine rises because the body needs it for repair. When intake does not meet that demand, recovery suffers, Mpho Tshukudu, a functional nutritionist, told The Epoch Times.

“Clinically, I often think of glycine as a buffering amino acid,” Duval said. “It helps create calm in inflamed systems, whether that’s the gut, brain, joints, or liver.”

Part of glycine’s anti-inflammatory effect appears to come from the way it helps regulate immune signaling. Glycine helps reduce the activation of inflammatory cytokines while also helping stabilize immune cell activity, she said.

Research is also exploring how glycine may affect aging. One study found that GlyNAC supplementation, a combination of glycine and N-acetylcysteine (NAC, a compound that helps the body make antioxidants), improved inflammation, insulin resistance, and cognitive function compared with a placebo, with benefits diminishing after participants stopped supplementation for 12 weeks.

Although the study examined the combined effects of glycine and NAC, researchers noted that glycine itself still appears to make important contributions to cellular health and organ function. Glycine supports energy production in cells and plays an important role in metabolic pathways linked to healthy aging and cellular repair.

How Modern Diets Created the Gap

The shift away from glycine-rich foods was not dramatic. It happened gradually, as convenience reshaped what we eat and how we cook.

“Traditional diets naturally contained far more glycine because they made use of slow-cooked meats, bone broths, skin, cartilage, tendons, and other connective tissue, often through whole-animal or nose-to-tail eating patterns,” she said.

Modern diets, on the other hand, tend to focus more heavily on muscle meat such as chicken breast, steak, and protein powders, which are higher in methionine (an amino acid needed for growth and repair) but relatively low in glycine. Over time, this can create an amino acid imbalance, Duval said.

“The cuts, bones, and slow-cooked preparations that were culinary staples for generations are no longer common because they take longer to cook,” Tshukudu said.

For many people, glycine intake is likely adequate to prevent deficiency. However, the result is an amino acid profile that looks adequate on paper but falls short where it counts: optimal repair, recovery, and glutathione synthesis.

How to Get More Glycine

Interestingly, rising food costs, growing interest in sustainability, and a renewed appreciation for nose-to-tail eating may be helping to shift this trend again, Tshukudu said.

From a practical standpoint, Duval suggested starting with simple dietary changes—including bone broth a few times per week and adding slow-cooked meats such as osso buco, lamb shanks, or beef cheeks. More skin-on preparations and connective tissue–rich cuts, such as oxtail and chicken wings, can also help increase intake naturally because they contain more of the tissues where glycine is concentrated.

Tshukudu also suggested increasing foods such as slow-cooked soups made with bone-in cuts, cooked until the connective tissue breaks down, as well as oxtail and fish with soft edible bones such as sardines.

Hydrolyzed collagen powders added to coffee, smoothies, or porridge are another option. For plant-based eaters, pumpkin seeds, spirulina, sesame seeds, lentils, and soy can be included in soups, salads, smoothies, and stews.

“I also encourage people to cook culturally and traditionally,” Tshukudu said. “Many ancestral food practices across African, Asian, Mediterranean, and Latin cuisines naturally included nose-to-tail eating and long-simmered dishes, which provided glycine without anyone needing to think about supplements.”

Glycine levels are not usually checked as part of a regular blood test. If you want to measure glycine specifically, you generally need a more specialized test, such as a plasma amino acid test, which measures different amino acids in the blood. Some healthcare professionals may also use urine tests to assess how the body breaks down and uses amino acids.

It’s worth knowing that glycine levels can be affected by what you have eaten recently, how much protein you eat, supplements, exercise, and your overall health, so results are not always straightforward to interpret.

Key Considerations

Before increasing glycine intake, it helps to understand that more is not always better, especially when the overall diet and lifestyle are not supporting recovery and repair.

One of the most common mistakes people make, Tshukudu said, is reaching straight for a collagen peptide supplement instead of first improving overall dietary quality.

Collagen supplements can add glycine to the diet, but glycine does not work in isolation. It competes with other amino acids for absorption and relies on cofactors such as vitamin B6, folate, and choline to function properly. If the overall diet is lacking in these nutrients, supplementation alone may not be enough, she said.

“Glycine is a good example of how modern nutrition can focus on isolated nutrients while overlooking the food traditions that supported health for generations,” Tshukudu said. “Research is increasingly catching up with those older practices.”