Muscle meat is high in amino acid methionine but comparatively poor in glycine. There has been a lot of discussion in the digital health community that high methionine intake—along with too little glycine—may encourage disease by causing imbalances in your body. This article explores in depth methionine and glycine, as well as their possible health effects.

Methionine and Glycine: What are they?

The amino acids are known as Methionine and Glycine. They make up the protein structure, along with 20 other amino acids. They are found in dietary protein and have many essential roles in the body.

Methionine

Methionine is a major amino acid. This means that the body wants it to work correctly, but it cannot generate it on its own. Your diet will meet your needs, as methionine is present in varying quantities in most dietary proteins—especially animal proteins. It is rich in egg whites, fish, beef, and some nuts and seeds.

Here are some popular foods rich in methionine

  • Dry egg whites: 2.8 grams per 3.5 ounces (100 grams)
  • Chicken breast: 0.9 grams per 3.5 ounces (100 grams)
  • Lean lamb: 1.1 grams per 3.5 ounces (100 grams)
  • Tuna: 0.9 grams per 3.5 ounces (100 grams) 
  • Lean beef: 1.1 grams per 3.5 ounces (100 grams)
  • Brazil nuts: 1.1 grams per 3.5 ounces (100 grams)
  • Bacon: 1.1 grams per 3.5 ounces (100 grams)
  • Dry spirulina: 1.2 grams per 3.5 ounces (100 grams)
  • Parmesan cheese: 1.0 gram per 3.5 ounces (100 grams)

One of the key purposes of methionine is to serve as a “methyl donor,” speeding up or sustaining chemical reactions within the body.

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Glycine

In the same way as methionine, glycine is present in different proportions in most dietary proteins. The richest dietary supply is animal protein collagen, the most abundant protein in humans and many animals. However, the meat you purchase in the store generally doesn’t have a lot of collagen—unless you want cheaper cuts.

It is located in connective tissue, tendons, ligaments, muscle, cartilage, and bones—all of which are typically associated with low-quality meat. Glycine is also abundant in gelatin, a material composed of collagen. Gelatin is widely used as a gelling agent in cooking and food processing.

Gelatin food outlets include gelatin sweets and gum bears. It is also an ingredient in several food items, such as milk, cream cheese, margarine, and ice cream.

Below are some examples of high-glycine foods:

Methionine
  • Dry gelatin powder: 19.1 grams per 3.5 ounces (100 grams)
  • Chicken skin: 3.3 grams per 3.5 ounces (100 grams)
  • Snacks of pork skin: 11.9 grams per 3.5 ounces (100 grams)
  • Lean lamb: 1.8 grams per 3.5 ounces (100 grammes)
  • Bacon: 2.6 grams per 3.5 ounces (100 grams)
  • Low-fat sesame flour: 3.4 grams per 3.5 oz (100 grams)
  • Dry egg whites: 2.8 grams per 3.5 ounces (100 grams)
  • Lean beef: 2.2 grams per 3.5 ounces (100 grams)
  • Cuttlefish: 2.0 grams per 3.5 ounces (100 grams)

Glycine is not a significant amino acid. This ensures you don’t need to get anything out of your food to survive. In reality, it can be created by your body from amino acid serine. Still, evidence shows that serine glycine synthesis can not meet all of the body’s needs for this amino acid. That’s why you would like to get a certain amount of money into your diet.

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Issues with Methionine

Muscle meat is moderately rich in methionine, which can be converted to another amino acid: homocysteine. Homocysteine is not present in fruit, unlike methionine. It is produced in your body as dietary methionine is metabolized, primarily in your liver. Excessive methionine intake can lead to increased levels of homocysteine in your blood—especially if you are deficient in certain nutrients, such as folate.

Homocysteine is particularly reactive in the body. High consumption of methionine from vitamins or animal proteins can have adverse effects on the function of blood vessels. Large serum homocysteine levels have been linked with many chronic diseases, such as heart disease.

That being said, there is no evidence that elevated homocysteine, in itself, causes heart disease. In particular, studies suggest that lowering homocysteine levels with folate or other B vitamins after a heart attack does not improve the risk of repeated events in the heart or circulatory system. Additionally, other findings show that homocysteine reduction techniques have little to no effect on heart disease or the likelihood of death.

Preservation of homocysteine balance

Methionine

Your body has a mechanism that holds homocysteine levels within a safe range. This includes, in particular, the recycling of homocysteine and its regeneration into amino acid cysteine or back to methionine. As this mechanism fails, the number of homocysteines increases. Methionine levels can also be down when homocysteine recycling is compromised.

There are three ways the body can reduce homocysteine levels. They are referred to as folate-dependent remethylation, folate-independent remethylation, and trans-sulphuration. For each of these to function, various nutrients are needed.

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Folate-Dependent Remethylation

This process transforms homocysteine back to methionine and helps to keep the base homocysteine levels low.

Three nutrients are required to keep the machine running smoothly:

  • Folate

This B vitamin is perhaps the most essential nutrient to sustain homocysteine levels within normal limits. 

  • Vitamin B12 

Vegetarians and vegans are also deficient in vitamin B12, which can induce a rise in homocysteine levels.

  • Riboflavin

While riboflavin is still required to make this process work, riboflavin supplements have limited effects on homocysteine levels.

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Folate-Remethylation Independent

This seems to be an alternative pathway that modifies homocysteine back to methionine or dimethylglycine, keeping basic homocysteine levels within a healthy and safe range.

For this pathway to work, several nutrients are needed:

  • Trimethylglycine or choline

Trimethylglycine is also known as betaine and is found in many plant foods. It can also be made from choline.

  • Serine and glycine

These two amino acids also appear to play a role in this phase.

Trans-Sulphuration

Methionine

This procedure reduces the homocysteine amount by converting it into an amino acid cysteine. It does not decrease the general level of homocysteine but may lessen the sharp rise in homocysteine levels after meals.

The nutrients needed to keep this process going include:

  • B6 Vitamin

When individuals are lacking in folate and riboflavin, low-dose vitamin B6 medications may effectively lower homocysteine levels.

  • Serine and glycine

Nutritional serine may also lower homocysteine levels after foods. Glycine has a similar impact.

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Does too much muscle meat lead to rising of homocysteine levels?

After eating a high-protein meal—or taking methionine supplements—homocysteine circulating increases within hours. The rise depends on the intensity of the dose.

Nevertheless, this rise occurs just temporarily after meals and is completely acceptable and normal. But on the other side, increasing your base level of homocysteine is more of a concern.

A larger volume dose of pure methionine is needed to increase the baseline level of homocysteine. One such dose was estimated to be approximately five times the normal daily intake of methionine, which is approximately 1 gram per day. Alternatively, smaller concentrations of doses do not increase the basic level of homocysteine

Simply put, there is no reason to show that a diet rich in muscle meat raises the essential amount of homocysteine in healthy individuals. While homocysteine is a product of methionine metabolism, dietary methionine intake is typically not the source of elevated base homocysteine levels. The root causes of elevated homocysteine levels include the failure of the body to keep it within a safe range. That includes food shortages, unsanitary lifestyle patterns, infections, and genetics.

Effects of Glycine

Glycine can decrease homocysteine levels after high protein meals. However, it is currently unclear if consuming lots of glycines has any impact on the baseline amount of homocysteine. More studies are required here. 

However, glycine supplements can have other health benefits. For example, oxidative stress, along with cysteine, has been shown to reduce in older adults. Besides, research shows that glycine supplements boost sleep quality.

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Conclusion

There is no clear reason to show that consuming too much methionine from muscle meat—or other food sources—causes a dangerous spike in homocysteine in healthy individuals. Nevertheless, this can depend on a variety of variables. For example, certain people with homocystinuria—a rare genetic mutation in the MTHFR gene—may respond differently. While glycine appears to play an important role in reducing the transient spike in homocysteine after a high-protein meal, its health importance remains uncertain. Several other nutrients are also essential for keeping homocysteine levels under control, most notably folate, vitamin B12, vitamin B6, choline, and trimethylglycine.