Bone Broth (Gelatin & Glycine)

What it is

Bone broth is bones and connective tissue (knuckles, feet, oxtail, skin) simmered in water for hours, usually with a splash of vinegar. The long heat breaks down collagen, the stiff protein that holds tendons, cartilage and skin together, into gelatin. Gelatin dissolves in hot water and sets into jelly when cold, which is the sign of a good broth.

Gelatin's amino acids look nothing like muscle meat's. It's about a third glycine, with large amounts of proline and hydroxyproline, plus some glutamate and glutamine. Muscle meat is rich in methionine and low in glycine, so broth balances a diet built on steaks and chicken breasts. For more on why that balance matters, see Glycine / Collagen.

Calms gut inflammation and protects the lining

In a 2021 mouse study, a beef bone broth was given as the mice's drinking water for 10 days before researchers chemically induced colitis, an inflammatory bowel disease. Compared with mice on water, the broth-fed mice had:¹

• A mostly intact gut lining, where the water group's was badly torn, with far fewer neutrophils (inflammatory white cells) moving into the tissue.
• More goblet cells, the cells that make the mucus layer. Mucus keeps bacteria off the gut wall and feeds some of the beneficial microbes that live in it.
• Lower inflammatory signals: IL-1β fell 61%, IL-6 95% and TNF-α 69%.
• Higher calming signals: IL-10 and IL-4 each rose more than five-fold. IFN-γ also rose, which can help switch on IL-10.

The physiology explains why broth's mix of amino acids would do this:

• Glutamine is the main fuel for the cells lining the gut, and they need it to keep the seals between them tight (see Glutamine).
• Glycine calms immune cells directly. Macrophages carry glycine-gated channels that, when opened, damp down their inflammatory response. Glycine is also needed to make glutathione, the gut lining's main antioxidant.
• Proline and hydroxyproline are the raw material for rebuilding the collagen framework under a damaged lining.

The mice got broth before the injury, so this shows protection, not a cure. No human studies have tested bone broth for gut inflammation.

Supplies glycine for sleep and glutathione

Human trials of glycine, taken as a powder, show it deepens sleep, helps rebuild glutathione and improves insulin sensitivity. Those trials are covered on the Glycine / Collagen page. Broth is a food route to the same amino acid.

How much broth delivers varies a lot. When broths were tested in a lab, homemade and café broths had far more glycine and proline than supermarket broths, and the same recipe gave consistent results batch to batch. Even good broth gave less than the 20 g collagen doses used in supplement research.² Broth that sets firmly in the fridge is the one doing the job. If you want a guaranteed dose, add a scoop of collagen or 1 tsp (3–5 g) of glycine powder to it.

Building blocks for joints and skin

Digestion doesn't break all of gelatin down to single amino acids. Short collagen fragments, such as hydroxyprolyl-glycine, survive and show up in the blood after people eat collagen.³ In cell studies these fragments signal fibroblasts, the cells that build collagen in skin, tendons and cartilage, to grow and make more.

Collagen supplements have human trials for skin and joint pain (see Glycine / Collagen). Broth delivers the same raw material in smaller and less predictable amounts. No human studies have tested broth itself for joints or skin.

Comfort food that helps when you're sick

When you're sick with fever or a stomach bug, you lose fluid and salt, and you often don't want to eat. Salted broth replaces both, and its amino acids give the gut lining fuel without much work to digest. That's basic physiology, and it's why broth is the traditional sick-day food (see Sodium).

There's also a lab finding behind the chicken-soup tradition. A homemade chicken soup slowed neutrophils, the white cells that pile into the airways during a cold, in a dose-dependent way, without harming the cells. The chicken and each of the vegetables contributed.⁴ No human studies have tested whether that eases cold symptoms.

How to make it

• Bones: use the parts with the most connective tissue: knuckles, feet, oxtail, necks and marrow bones. Beef, chicken and pork all work. Chicken feet set into the firmest jelly.
• Water: about 2 quarts of water per pound of bones (the mouse study used 1 part bone to 4 parts water by weight). Just covering the bones gives a richer broth.
• Vinegar: 4 tsp of white vinegar per quart of water, as in the study. The acid helps loosen collagen from the bone.
• Time: simmer at least 8 hours on the stove or in a slow cooker, topping up with water as needed. A pressure cooker does it in 2–3 hours (see the Gelatin Chicken Soup and Pho recipes).
• Finish: strain, chill, and lift off the fat. It should set like jelly. Keep it 4–5 days in the fridge, or freeze it in portions.
• Amount: 1–2 cups a day, salted to taste.

Safety

Histamine and glutamate: long cooking and days in the fridge raise both. Most people won't notice, but anyone who gets headaches, flushing or a racing heart from aged or fermented foods may react to broth too. Shorter pressure-cooker broths, frozen promptly, are gentler. Store-bought: boxed broth often doesn't set and has little gelatin; look for one that's solid when cold.