Glycine: which foods contain it?

What is glycine?

Glycine is an amino acid, one of the building blocks of proteins. According to the PubChem record of the U.S. National Library of Medicine, it is the simplest of the amino acids found in proteins: its side chain is a single hydrogen atom. It is classed as a nonessential amino acid. It is therefore present in every food that contains protein, in very different amounts.

Which foods contain the most?

The USDA FoodData Central database lists the glycine content of many foods. The table shows a few common foods from its SR Legacy data, released in April 2018, per 100 g of the food as described in each record.

Protein-rich plant foods such as soybeans, peanuts and lentils have amounts in the same range as salmon or chicken. The differences come mainly from how much protein each food contains.

Glycine as a share of protein

Comparing grams of glycine per 100 grams of food mixes two things: how much protein the food contains and how much of that protein is glycine. Dividing glycine by protein separates them. The last column was calculated by this page from the records cited.

Two groups appear. Foods made largely of collagen, gelatin and pork rinds, have a glycine share of about 19% to 22%. Every other food in the table sits between about 2% and 6%. Within that second group the differences in glycine per 100 grams are mostly differences in how much protein the food contains, which is why soybeans and salmon, with a similar share, differ by roughly a factor of two in glycine per 100 grams.

Why does gelatin come first?

The review by Shoulders and Raines (Annual Review of Biochemistry, 2009) notes that collagen is the most abundant protein in animals. Its triple-helix structure requires every third amino acid to be glycine: the chain repeats a three-unit pattern whose third unit is always glycine. Gelatin is a protein obtained from collagen.

According to Gelatine Manufacturers of Europe (GME), about 80% of the edible gelatin produced in Europe is made from pigskin, 15% from a layer of cattle hide called split, and the remaining 5% from pork and cattle bones and fish. In the USDA data, glycine makes up about 22% of the protein in gelatin powder, compared with about 5% for soybeans or salmon (calculated by this page from the records cited).

What the numbers describe, and what they do not

Most values in the table are for raw foods, and the sources read do not say what happens to glycine during cooking. Foods are also compared as the database describes them: gelatin powder is a dry product with 85.6 grams of protein per 100 grams, whereas whole milk is mostly water with 3.15 grams. A cooked, dried or processed version of the same food will have a different composition, so a figure from the table cannot be carried over to a dish.

It follows that the table answers one question only: in which foods is glycine found, and in what proportion? The page does not rank foods as better or worse, and it gives no amount to aim for. The database is American and dates from 2018, so a product sold elsewhere may differ.

Glycine on an ingredient list

Glycine can also appear on an ingredient list as a food additive. In the United Kingdom, the Food Standards Agency includes glycine and its sodium salt in its list of approved additives, as E640. This page says nothing about the use of this additive in any specific product.

A word about collagen and gelatin

Shoulders and Raines (2009) explain why gelatin comes first: in the triple helix of collagen, every third amino acid is glycine, and gelatin is obtained from collagen.² The Gelatine Manufacturers of Europe add that about 80% of the edible gelatin produced in Europe comes from pigskin, 15% from split, a layer of cattle hide, and the rest from pork and cattle bones and fish.³ That is a matter of origin, not of content per portion: the amount of gelatin in a dish depends on the recipe.

For other food composition pages, see astaxanthin, taurine and betaine. The additive E640 and other label wording are explained in how to read a food label. The group is collected in food composition guides.

What this page does not say

• It attributes no property to glycine.
• It recommends no amount, per day or per meal.
• The values describe foods in a 2018 U.S. database; a product sold elsewhere may differ.
• Most values are for raw foods; the sources read do not say what happens to glycine during cooking.

When to ask for advice

To adapt your diet to your situation, a doctor or dietitian can advise you. This page presents food composition data and does not replace medical advice.

Frequently asked questions