March, 2016

Methionine vs Glycine – Is Too Much Muscle Meat Bad?

Muscle meat is rich in the amino acid methionine, but relatively low in glycine. In the online health community, there has been a lot of speculation that a high intake of methionine, along with too little glycine, may promote disease by causing an imbalance in the body. This article takes a detailed look at the science behind these ideas.

What Are Methionine and Glycine?

Methionine and glycine are amino acids. They make up the structure of proteins, along with 20 other amino acids. They are found in dietary protein and also have many important functions in the body.


Methionine is an essential amino acid. This means that we need to get it from the diet in order to survive. Luckily, methionine is easy to acquire. It is found in varying amounts in most dietary protein, especially animal protein. It is abundant in egg whites, seafood, meat and certain nuts and seeds. Below are some examples of foods that are high in methionine (1):

  • Dried egg whites: 2.79 g/100 g.
  • Dried spirulina: 1.15 g/100 g.
  • Lean beef: 1.14 g/100 g.
  • Brazil nuts: 1.12 g/100 g.
  • Lean lamb: 1.09/100 g.
  • Bacon: 1.07 g/100 g.
  • Parmesan cheese: 0.96 g/100 g.
  • Chicken breast: 0.92 g/100 g.
  • Tuna: 0.88 g/100 g.

One of methionine’s main functions is to serve as a “methyl donor”, speeding up or maintaining chemical reactions within the body.

Bottom Line: Methionine is an essential amino acid, abundant in eggs, seafood and meat.


Similarly to methionine, glycine is found in varying amounts in most dietary protein. The richest dietary source is the animal protein collagen, which is the most abundant protein in humans and many animals. However, collagen is usually not found in high amounts in the meat you buy at the supermarket, unless you prefer cheaper cuts. It is found in connective tissue, tendons and ligaments, skin, cartilage and bones–stuff that is usually associated with low-quality meat. Glycine is also found in high amounts in gelatin, a substance made from collagen. Gelatin is commonly used as a gelling agent in cooking and food production. Dietary sources of gelatin include gelatin desserts and gummy bears. It is also an additive in various food products, such as yogurt, cream cheese, margarine and ice cream. Below are some examples of glycine-rich foods:

  • Dry gelatin powder: 19.05 g/100 g.
  • Pork skin snacks: 11.92 g/100 g.
  • Low-fat sesame flour: 3.43 g/100 g.
  • Chicken skin: 3.25 g/100 g.
  • Dried egg whites: 2.84 g/100 g.
  • Bacon: 2.60 g/100 g.
  • Lean beef: 2.17 g/100 g.
  • Cuttlefish: 2.03 g/100 g.
  • Lean lamb: 1.75 g/100 g.

Glycine is not an essential amino acid. This means that we don’t need to get it from the diet to survive. In fact, the body can produce it from the amino acid serine. However, evidence suggests that glycine synthesis from serine may not fulfill all of the body’s need for glycine. That’s why we may need to get a certain amount from the diet.

Bottom Line: Glycine is a non-essential amino acid found in high amounts in skin, connective tissue, ligaments, tendons, cartilage and bones.

What’s the Problem With Methionine?

Muscle meat is relatively high in methionine, which can be turned into another amino acid called homocysteine. Unlike methionine, homocysteine is not found in food. It is formed in the body when dietary methionine is metabolized, mainly in the liver. Excessive consumption of methionine may lead to elevated levels of homocysteine in the blood, especially when people are deficient in certain nutrients, such as folate. Homocysteine is highly reactive within the body, which makes it potentially harmful in high amounts. In fact, high levels of homocysteine have been associated with several chronic diseases, such as heart disease. Because of this, methionine supplements or animal protein may have adverse effects on the function of blood vessels. However, there is currently no strong evidence that elevated homocysteine, in itself, causes heart disease. It may simply be an indirect risk factor, statistically associated with the true cause. A few studies have shown that reducing homocysteine levels with folate or other B-vitamins after a heart attack does not decrease the frequency of recurrent events in the heart or circulatory system. Additionally, meta-analyses found that reducing homocysteine levels had little or no effects on future heart disease events or the risk of death

Bottom Line: High amounts of methionine may lead to elevated levels of homocysteine. Homocysteine has been linked with heart disease and other chronic diseases, but whether it actually causes them is a matter of debate.

Maintenance of Homocysteine Balance

The body has a system to keep homocysteine levels within a healthy range. This mainly involves recycling homocysteine and turning it into the amino acid cysteine or back to methionine. When this system fails, homocysteine levels increase. Levels of methionine may also run low when homocysteine recycling is impaired. There are three ways by which the body can reduce homocysteine levels. They are called folate-dependent remethylation, folate-independent remethylation and trans-sulphuration. Different nutrients are required for each of these three mechanisms to work.

1. Folate-dependent remethylation: This process converts homocysteine back into methionine, and helps keep base levels of homocysteine low. Three nutrients are required to keep this system running smoothly:

  • Folate: This B-vitamin is probably the most important nutrient for maintaining homocysteine levels within normal limits.
  • Vitamin B12: Vegetarians are often low in vitamin B12, which may cause an increase in homocysteine levels.
  • Riboflavin: Although riboflavin is also necessary to make this process work, riboflavin supplementation has limited effects on homocysteine levels.

2. Folate-independent remethylation: This is an alternative pathway that changes homocysteine back into methionine or dimethylglycine, keeping base levels of homocysteine within a healthy range. Several nutrients are needed for this pathway to work:

  • Trimethylglycine or choline: Also called betaine, trimethylglycine is found in many plant foods. It can also be produced from choline.
  • Serine and glycine.

3. Trans-sulphuration: This process lowers homocysteine levels by turning it into the amino acid cysteine. It does not lower base levels of homocysteine, but may reduce the spike in homocysteine levels after meals. The nutrients required to keep this process running include:

  • Vitamin B6: When people are deficient in folate and riboflavin, low-dose vitamin B6 supplementation may effectively lower homocysteine levels.
  • Serine: Dietary serine may also reduce homocysteine levels after meals. Glycine has similar effects.

If these systems do not work efficiently, circulating homocysteine levels may rise. However, nutrients are not the only factors that may affect homocysteine levels. Genetics (such as the MTHFR gene), age, certain drugs, and conditions, such as liver disease and metabolic syndrome, also play a role.

Bottom Line: Under normal circumstances, the body keeps homocysteine levels within a healthy range. This requires several nutrients, such as folate, vitamin B12, vitamin B6, trimethylglycine, serine and glycine.

Does Too Much Muscle Meat Increase Homocysteine Levels?

After eating a high-protein meal, or taking methionine supplements, circulating homocysteine increases within hours. The level of increase depends on the dose. However, this increase only occurs temporarily after meals, and is perfectly normal. On the other hand, an increase in the base level of homocysteine is more of a concern. To increase base levels of homocysteine, a high dose of pure methionine is required. This dose has been estimated to be equivalent to about 5 times the normal daily intake of methionine. Conversely, lower doses do not increase base levels of homocysteine. Simply put, there is no evidence that a diet high in muscle meat increases base levels of homocysteine in healthy people. Although homocysteine is a product of methionine metabolism, dietary methionine intake is generally not the cause of elevated base homocysteine levels. The underlying causes of elevated homocysteine involve the body’s inability to keep it within a healthy range. These include nutrient deficiencies, unhealthy lifestyle habits, diseases and genetics.

Bottom Line: A high dose of supplemental methionine may increase base levels of homocysteine. On the other hand, eating muscle meat only leads to a temporary increase in homocysteine levels that subsides soon afterwards.

How Does Glycine Step In?

Glycine may reduce homocysteine levels following high-protein meals. However, whether eating a lot of glycine has any effects on the base levels of homocysteine is currently unknown. More studies are needed. On a different note, glycine supplementation may have some health benefits. For example, it has been shown to decrease oxidative stress in elderly people, along with cysteine, and other studies suggest that glycine supplementation improves sleep quality.

Bottom Line: Dietary glycine may help reduce the temporary rise in homocysteine levels after a high-protein meal. The health relevance of this is unclear.

Take Home Message

There is no good evidence that getting too much methionine from muscle meat, or other dietary sources, causes a harmful rise in homocysteine in healthy humans. However, this may depend on several factors. For example, some people with a mutation in the MTHFR gene may respond differently. Although glycine appears to play an important role in reducing the temporary rise in homocysteine after a high-protein meal, its health relevance remains unclear. Several other nutrients are also important for keeping homocysteine levels under control. The most important of these are folate, vitamin B12, vitamin B6, choline and trimethylglycine. If you eat lots of methionine-rich food, such as eggs, fish or meat, make sure you’re getting plenty of these nutrients as well.

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How Probiotics Can Help You Lose Weight and Belly Fat

Probiotics are live microorganisms that have health benefits when eaten. They are found in both supplements and fermented foods. Probiotics may improve digestive health, heart health and immune function, to name a few. Several studies also suggest that probiotics can help you lose weight and belly fat.

Gut Bacteria May Play a Role in Body Weight Regulation

There are hundreds of different microorganisms in your digestive system. The majority of these are bacteria, most of which are friendly. Friendly bacteria produce several important nutrients, including vitamin K and certain B-vitamins. They also help break down fiber that the body can’t digest, turning it into beneficial short-chain fatty acids like butyrate. There are two main families of good bacteria in the gut: bacteroidetes and firmicutes. Body weight seems be related to the balance of these two families of bacteria.

Both human and animal studies have found that normal-weight people have different gut bacteria than overweight or obese people. In those studies, people with obesity had more firmicutes and fewer bacteroidetes, compared to normal-weight people. There are also some animal studies showing that when the gut bacteria from obese mice are transplanted into guts of lean mice, the lean mice get fat.

All of these studies suggest that gut bacteria may play a powerful role in weight regulation.

Bottom Line: There are many different microorganisms in the gut, mostly bacteria. Several lines of evidence suggest that these gut bacteria can have powerful effects on body weight.

How Can Probiotics Affect Changes in Weight?

It is thought that certain probiotics may inhibit the absorption of dietary fat, increasing the amount of fat excreted with feces. In other words, they make you “harvest” fewer calories from the foods in your diet. Certain bacteria, such as those from the Lactobacillus family, have been found to function in this way. Probiotics may also fight obesity in other ways:

  • Release of GLP-1: Probiotics may help release the satiety (appetite-reducing) hormone GLP-1. Increased levels of this hormone may help you burn calories and fat.
  • Increase of ANGPTL4: Probiotics may increase levels of the protein ANGPTL4. This may lead to decreased fat storage.

There is also a lot of evidence that obesity is partly caused by inflammation in the brain. By improving gut health, probiotics may reduce systemic inflammation and protect against obesity and other diseases. However, it is important to keep in mind that these mechanisms aren’t understood very well. More research is needed.

Bottom Line: Probiotics may reduce the number of calories you absorb from food. They also affect hormones and proteins related to appetite and fat storage. They may also reduce inflammation, which can drive obesity.

Probiotics May Help You Lose Weight and Belly Fat

Studies have found that certain strains of the Lactobacillus family can help you lose weight and belly fat. In one study, eating yogurt with Lactobacillus fermentum or Lactobacillus amylovorus reduced body fat by 3–4% over a 6-week period. Another study of 125 overweight dieters investigated the effects of Lactobacillus rhamnosus supplements on weight loss and weight maintenance. During a 3-month study period, the women taking the probiotics lost 50% more weight compared to the group taking a dummy pill (placebo). They also continued to lose weight during the weight maintenance phase of the study.

Lactobacillus Gasseri

Of all the probiotic bacteria studied to date, Lactobacillus gasseri shows the most promising effects on weight loss. Numerous studies in rodents have found that it has anti-obesity effects. Additionally, studies in Japanese adults have shown impressive results. One study followed 210 people with a lot of belly fat. It found that taking Lactobacillus gasseri for 12 weeks reduced body weight, fat around organs, BMI, waist size and hip circumference. What’s more, belly fat was reduced by 8.5%. However, when participants stopped taking the probiotic, they gained back all of the belly fat within a month.

Bottom Line: Some strains of the Lactobacillus family have been shown to reduce weight and belly fat in studies. Lactobacillus gasseri appears to be the most effective.

Some Probiotics May Prevent Weight Gain

Losing weight is not the only way to fight obesity. Prevention is even more important, as in preventing the weight from accumulating in the first place. In one 4-week study, taking a probiotic formulation called VSL#3 reduced weight gain and fat gain on a diet where people were overfed by 1000 calories per day. On this graph, you can see how the probiotic group gained significantly less fat:

What this indicates, is that some probiotic strains might be effective at preventing weight gain in the context of a high-calorie diet. However, this needs to be studied a lot more.

Bottom Line: Certain probiotic strains may be able to prevent weight gain on a high-calorie diet.

Some Probiotic Strains May Increase the Risk of Weight Gain and Obesity

Not all studies have found that probiotics help with weight loss. Some studies have even found that certain probiotic strains might lead to weight gain, not loss. This includes Lactobacillus acidophilus, Lactobacillus fermentum and Lactobacillus ingluviei. One recent study reviewed 4 controlled clinical trials. It concluded that probiotics did not reduce body weight, BMI or body fat levels in overweight or obese adults. However, this review study did not include many of the studies mentioned above.

Bottom Line: Not all probiotics help with weight loss, and some of them may even cause weight gain. The effects depend on the probiotic strain, and may also vary between individuals.

Probiotics May be One Part of The Puzzle

Probiotics offer a wide range of health benefits. However, their effects on weight are mixed, and seem to depend on the type of probiotic. According to the studies, Lactobacillus gasseri may help people with obesity lose weight and belly fat. Additionally, a blend of probiotics called VSL#3 may reduce weight gain on a high-calorie diet. At the end of the day, certain types of probiotics may have modest effects on your weight, especially when combined with a healthy, real food-based diet. However, there are many other reasons to take a probiotic supplement besides weight loss. They can improve digestive health, reduce inflammation, improve cardiovascular risk factors and even help fight depression and anxiety.

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