Glycine

Glycine: The Pro-Metabolic Amino Acid

The following is a quote from Ray Peat's article titled "Gelatin, stress, and longevity"

"A generous supply of glycine/gelatin, against a balanced background of amino acids, has a great variety of antistress actions. Glycine is recognized as an “inhibitory” neurotransmitter, and promotes natural sleep. Used as a supplement, it has helped to promote recovery from strokes and seizures, and to improve learning and memory. But in every type of cell, it apparently has the same kind of quieting, protective antistress action. The range of injuries produced by an excess of tryptophan and serotonin seems to be prevented or corrected by a generous supply of glycine. Fibrosis, free radical damage, inflammation, cell death from ATP depletion or calcium overload, mitochondrial damage, diabetes, etc., can be prevented or alleviated by glycine." 

Glycine is used in the body to produce glutathione, heme, creatine, collagen, bile, and nucleic acids. It is considered a 'non-essential' amino acid by some, and a 'conditionally essential' amino acid by others, but there is sufficient evidence to support that the amount of glycine we synthesize within our bodies is not enough to meet the demands of our daily stressors.

Glycine, like taurine, is a component of bile acids, which are crucial to our digestion of fat and assimilation of fat-soluble vitamins. This makes it a very important amino acid for liver health and detoxification.

Glycine supplementation is observed to have many benefits on the metabolic, nervous, and endocrine systems. Improving insulin sensitivity, reducing blood glucose, inhibiting excitatory neurotransmitters, improving sleep quality, promoting wound healing and cognition are of the many known benefits of glycine supplementation. 

Conversely, a deficiency of serum glycine can be observed in many cases of metabolic disorders such as diabetes, obesity, hypertension, hyperlipidemia and fatty liver. 

It was Ray, maybe alongside Weston. A. Price, who really highlighted and popularized the notion of 'nose-to-tail' eating, and returning to a more traditional way of consuming the whole animal, as each part has its own nutritional characteristics and benefits, and without them we may fall out of balance. He mainly highlighted this because of the fact that around 50% of all protein in an animal is collagen, which is what becomes gelatin when cooked. Of that gelatin, about 35% of all amino acids within it are glycine.

Highly industrialized societies have gravitated away from the consumption of nose-to-tail collagenous meats, in favor of pure muscle meats such as chicken breasts and steaks as the main protein sources.
Eating this way over a lifetime, and as a majority of the diet will cause severe amino acid imbalance, with glycine deficiencies and excess of cysteine, tryptophan, and methionine which can become anti-metabolic and inflammatory. Glycine supplementation has shown to be incredibly valuable in this context.