The Dangers of Methionine, Cysteine, and Tryptophan in Animal Protein

The problem with eating muscle meat is that it is high in the amino acids tryptophan and glycine, which causes inflammation.

When most people eat meat, they don’t eat bones or organs (such as the animal’s liver). They eat muscle meat. The problem with eating muscle meat is that it is high in the amino acids tryptophan and cysteine, which causes inflammation.

According to Dr Ray Peat’s Gelatin, Stress, Longevity:

In the industrialized societies, the consumption of gelatin has decreased, relative to the foods that contain an inappropriately high proportion of the antimetabolic amino acids, especially tryptophan and cysteine…. When only the muscle meats are eaten, the amino acid balance entering our blood stream is the same as that produced by extreme stress, when cortisol excess causes our muscles to be broken down to provide energy and material for repair. The formation of serotonin is increased by the excess tryptophan in muscle, and serotonin stimulates the formation of more cortisol, while the tryptophan itself, along with the excess muscle-derived cysteine, suppresses the thyroid function.

The Paleo website paleoleap.com adds (Why Eating the Off Bits Improves Your Health) that in addition to the dangers of tryptophan and cysteine, muscle meats are high in methionine. Restricting methionine can have significant beneficial impacts on health:

Most people today only muscle meat, with hardly any organ meat and bones and very little skin, so they eat a whole lot of methionine and not a lot of glycine…. Essentially, methionine restriction increases lifespan and improves metabolic health (body fat accumulation, insulin sensitivity, blood lipids, and all the related issues). This was mostly done in animal studies, but in human trials, a low-methionine diet also improved liver health and increased the rate of fat burning.

Denise Minger says the following:

 Constant abundance and pickiness is absolutely new to our bodies, even for those of us eating foods we deem ancient or ancestral. So it’s really not all that far-fetched to think that America’s animal protein habits—heavy on the methionine-rich muscle meats, scant on the glycine, swimming in ceaseless surplus instead of punctuated with scarcity—could be a problem for our health…. Perhaps it’s not a coincidence that many of the world’s longest-living populations eat fairly low-methionine diets or periodically abstain from protein-rich foods (like in Ikaria, where the predominantly Orthodox Christian residents cyclically fast from animal products). And perhaps just as relevant as the types of foods we eat is the manner in which we eat them—nose-to-tail for animals, with some plant-only days thrown in for good measure.

Why I’m Not Dismissing the Latest “Animal Protein is Bad” Study (But Not Losing Sleep Over It, Either)

Methionine increases IGF 1, which feeds cancer; cysteine suppresses the thyroid gland; and tryptophan increases inflammation and causes liver damage. The answer, according to Dr Ray Peat and according to the Paleos, is to consume large quantities of the amino acid glycine, which neutralises the damaging effects of muscle meats. Animal food that is high in glycine include bone, cartilage, tendons, intestines, kidneys, and liver.

However, who wants to eat bone?

When I was a meat eater, I remember how delicious muscle meats were. Any mention of intestines or liver would almost make me gag in disgust. All this reminds me of Paleo Pete Evans’s cookbook for babies that recommend bone broth rather than infant formula. Pete was put under investigation by federal health authorities.

A danger with eating animal organs such as liver is that the organs of animals have very high concentration of heavy metals such as cadmium. Cadmium is a highly toxic metal. According to one study, cadmium exposure may impair cognitive performance even at levels once thought to be safe. According to Dr Michael Gregor (How to Reduce Your Dietary Cadmium Absorption), cadmium concentration is highest in animal organs (including horse kidney and pig kidney) as well as seafood. Only one tablespoon of pig kidney was enough to exceed the daily safety limit of cadmium.

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There is little cadmium in muscle meat, very high cadmium in animal organs, and moderate amounts of cadmium in vegetables and grain. However, cadmium in vegetables and grain are not absorbed efficiently in the body due to the presence of fiber and phytates. Dr Gregor goes on to say the following:

Cadmium bioavailability from animal-based foods may be higher than that from vegetable-based foods. There appears to be something in plants that inhibits cadmium absorption. In fact, researchers found when they added kale to boiled pig kidneys, they could cut down on the toxic exposure. Just one tablespoon of pig kidney, and we may exceed the daily safety limit—unless we add kale, in which case we could eat a whole quarter cup. The pronounced effects of the inhibitory factors in kale point out, as the researchers note, “the importance of vegetable foods in terms of prevention of health hazard from [cadmium] ingested as mixed diets in a real situation.”

Rather than cooking up bone broth, eating animal cartilage, or eating liver or kidney, a much easier way to get more glycine into your body (as opposed to tryptophan, cysteine, and methionine) is to consume plant protein. Looking only at concentration of glycine and tryptophan and looking at the amino acid profile of protein powders at bulknutrients.com.au, I have created the table below, which shows how plant proteins (pea protein and rice protein) are high in glycine. Compare this to the amino acid profile of whey protein, which is an animal protein.

Protein Type Tryptophan Glycine Tryptophan-Glycine Ratio
Rice Protein Isolate 770mg per 100g 4050mg per 100g 0.19
Pea Protein Isolate 570mg per 100g 2810mg per 100g 0.20
Whey Protein Isolate 580mg per 30g 435mg per 30g 1.33

2 thoughts on “The Dangers of Methionine, Cysteine, and Tryptophan in Animal Protein”

  1. Is this a mistake, “The problem with eating muscle meat is that it is high in the amino acids tryptophan and glycine, which causes inflammation.” Don’t you mean cysteine, and not glycine?

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