L-Threonine for Gut Health & Muscle Growth

A Rarely Discussed Essential Amino Acid that is Surprisingly Powerful

In this next article, we investigate the essential amino acid L-Threonine.

As I’m researching this amino acid, I’m blown away by how rarely this powerhouse molecule is discussed.

Here are some of the key physiological functions of L-Threonine:

• Prioritized for the structure & function of the gut

• Balances the microbiome by selectively feeding commensal organisms

• Regulates immunity, inflammation, and fat metabolism (especially in the liver)

• A limiting substrate for muscle growth and collagen repair

• Regulates embryonic stem cell self-renewal and cell growth

• Breaks down to critical substrates including Acetyl CoA, pyruvate, & glycine

• Increases glycine levels in the brain & decreases muscle tone & spasticity

While also references are including at the end, I must credit this excellent recent paper that comprehensively evaluates the physiological functions of L-Threonine.

Here are 4 key roles of L-Threonine, a mighty amino acid.

1. Gut Health

While “gut health” has become a sort of buzz word, it’s difficult to overstate the importance of L-Threonine in this regard. 71% of total L-Threonine is used by the gut to synthesize mucosal proteins. (1)

L-Threonine also regulates the immune system and feeds the commensal bacteria that produce critical substrates needed to regenerate the gut lining, such as butyric acid. (3) Butyric acid is a powerful molecule and is sometimes supplemented by itself for its potential benefits regarding gut health and microbial balance. For example, “butyric acid resulted in normalization of symptoms in 71% of patients with IBS-D and in 16% of patients with IBS-C”. (6)

By maintaining gastrointestinal health and integrity we can digest and assimilate nutrients more effectively, including the other essential amino acids - all of which are needed to build muscle and strength.

Gastrointestinal function is a critical factor for body composition and performance that is often underappreciated and poorly understood, especially given the prevalence of gastrointestinal disorders such as IBS & IBD.

2. Muscle Growth

L-Threonine may promote growth & support protein synthesis of skeletal muscle through several mechanisms.

First, by generating glycine, which modulates protein synthesis by activating mTOR and suppressing muscle protein breakdown.

Second, by regulating the protein synthesis pathway via IGF-1.

Third, L-Threonine is an essential amino acid, all of which are necessary for protein synthesis. The body will prioritize L-Threonine’s role in the gut and immune system before it contributes L-Threonine to building muscle. Thus, suboptimal intake of L-Threonine may impair growth & recovery. For survival, digestion and immunity take precedence over size and strength.

Fourth, L-Threonine regulates cellular growth & proliferation while providing metabolic fuel for embryonic stem cells which are studied for therapeutic potential with various conditions.

Fifth, L-Threonine regulates immunity and inflammation. Hypertrophy and physical adaptations are an immune system process. Exercise induces damage and inflammation in order to elicit an adaptation, which places a demand on the immune system.

Inflammation in the gut may also decrease exercise performance, especially in situations involving bloating and pain. Thus, by regulating inflammation and immune function, L-Threonine directly and indirectly influences training outcomes.

3. Collagen Repair

Glycine is a major component of collagen. Collagen powder is a popular supplement for its ability to support skin, hair, nails, and connective tissue health. Glycine is a major ingredient in collagen powder.

Actually, glycine alone makes up 11.5% of the amino acid content in the human body, and 80% of whole body glycine is used for protein synthesis. Glycine also regulates the synthesis of cytokines and production of superoxide - it is critical for immune function. (4)

Strong, healthy connective tissue is obviously important for athletic purposes.

Glycine is also used for sleep, treatment of GI disorders, and as an antioxidant.

What does this have to do with L-Threonine?

L-Threonine is a precursor to Glycine. Furthermore, Glycine poorly crosses the blood brain barrier. By increasing glycine levels in the brain, L-Threonine supplementation has been found to reduce spasticity and improve muscle tone. (5)

This might improve sleep and enhance relaxation, an additional mechanism by which this amino acid may improve tissue repair. Hypertonicity and chronic inflammation from muscle tension impairs recovery and can negatively effect posture and movement patterns in a way that deteriorates collagen.

4. Energy Production

While most L-Threonine is used in the gut, L-Threonine is also a key player in energy production through several mechanisms that are relatively straight-forward.

The liver is an important storage unit for energy in the form of triglycerides, and L-Threonine regulates lipid metabolism in the liver. This also potentially reduces fat accumulation and may protect us from developing fatty liver disease.

L-Threonine is also broken down to glycine, acetyl CoA, and pyruvate, all of which are used for energy production in the tricarboxylic acid cycle.

Finally, since L-Threonine’s priority is in the gut and it plays such a fundamental role in nutrient absorption and assimilation, optimal L-Threonine intake supports energy by enhancing intestinal digestion and absorption and balancing the microbiota.

The specific organisms L-Threonine feeds produce short chain fatty acids that can also be used efficiently for energy such as butyric acid.

Summary

As an essential amino acid, we begin with an understanding that this nutrient is necessary for hypertrophy and protein synthesis in general.

However, L-Threonine plays a surprisingly critical role for gut health and we must consider optimal intake for athletes because gastrointestinal demands must be met in before L-Threonine is allotted for building muscle and repairing collagen.

Aside from directly contributing to gut structure and function as well as microbial balance, by regulating inflammation and immunity we can increase.

L-Threonine also may play a key role in recovery given its role as a precursor to glycine and its ability to increase glycine in cerebrospinal fluid in a way glycine alone cannot, while decreasing muscle tone and spasticity.

I personally use upwards of 6g of supplemental L-Threonine with excellent results. That also happens to be the amount used in the spasticity study. (5)

While optimal intake for humans is debated as it is for virtually any nutrient, especially given optimal intake is multi-factorial and dynamic, I hope this article sheds light on this rarely discussed essential amino acid.

In strength,

Daniel J. Furtado, CPT, LMT, Owner of Honor Strength
www.honorstrength.com

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References

1. Specific roles of threonine in intestinal mucosal integrity and barrier function

2. Specific amino acids increase mucin synthesis and microbiota in dextran sulfate sodium-treated rats.

3. The Role of Microbial Amino Acid Metabolism in Host Metabolism

4. Multifarious Beneficial Effect of Nonessential Amino Acid, Glycine: A Review

5. A double-blind study of L-threonine in patients with spinal spasticity

6. Efficacy of butyrate in the treatment of diarrhoea-predominant irritable bowel syndrome