By Biplab Das

What is Threonine? 

Threonine is one of the 20 amino acids that constitute proteins. It is an essential amino acid and not synthesized by humans. Therefore, threonine has to be obtained from dietary sources. Threonine can exist in four possible forms or two forms of L-threonine. The name L-threonine is mostly used for one single form chemically known as (2S, 3R)-2-amino-3-hydroxybutanoic acid. L-threonine is one of three indispensable amino acids since mammals do not possess the necessary enzymes for the transamination of threonine. Another form, called L-allo-threonine, is rarely present in nature. In plants and microorganisms, threonine is synthesized from aspartic acid via alpha-aspartyl-semialdehyde and homoserine.

Health Benefits of Threonine 

Threonine supports cardiovascular, liver, central nervous, and immune system function. Threonine aids in the synthesis of glycine and serine, two amino acids that help in the production of collagen, elastin, and muscle tissue. Threonine helps build strong bones and tooth enamel. It also speeds up wound healing after injury by boosting immune system. Threonine combines with the amino acids aspartic acid and methionine to help liver digest fats and fatty acids, which reduces accumulation of fat in the liver. An accumulation of fats in the liver can affect negatively its function. Threonine is useful in treating Lou Gherig’s Disease, also known as Amyotropic Lateral Sclerosis (ALS). Research shows that symptoms of Multiple Sclerosis (MS), another disease that affects nerve and muscle, are alleviated with threonine treatment. Threonine is an immunostimulant, which promotes the growth of thymus gland.

Threonine Deficiency

A study with animals (piglets) has shown that threonine deficiency has caused higher nitrogen excretion and higher blood urea. Histpathological analyses showed lower number of acidic mucin-producing goblet cells in the duodenum and ileum (parts of small intestine) of pigs fed with threonine-deficient diet. Dietary threonine imbalance is known to reduce the growth of the small intestine, liver, and skeletal muscle in young animals. Piglets fed deficient threonine diets had smaller intestinal weights, less mucosal tissue (the absorptive cells of the intestine), and less intestinal mucin (Mucin is mucous that lines the interior surface of the digestive organs like small intestine) compared to control pigs.

Food Sources of Threonine 

Threonine is found in meats, fish, dairy foods, eggs, bananas, and carrots. Wheat germ, many nuts, beans, seeds and vegetables also contain threonine but to a small level. Research shows that mean requirement of threonine for healthy adults is 15 mg per kilogram of body weight per day.

 
Table: List of foods containing amino acid threonine (ordered high to low, grams/100 grams food portion).

Data source: USDA National Nutrient Database for Standard Reference, Release 19 (2006).

1. Garson K. Law, Robert F. Bertolo, Alfred Adjiri-Awere, Paul B. Pencharz, and Ronald O. Ball. Adequate oral threonine is critical for mucin production and gut function in neonatal piglets. May 1 2007, AJP – Gastrointestinal and Liver Physiology, Vol. 292 (5), G1293- G1301.

2. Sudhir Borgonha, Meredith M Regan, Seung-Ho Oh, Mervelina Condon and Vernon R Young. Threonine requirement of healthy adults, derived with a 24-h indicator amino acid balance technique. April 2002, American Journal of Clinical Nutrition. Vol. 75 (4), 698-704.

3. Xu Wang, Shiyan Qiao, Yulong Yin, Longyao Yue, Zongyi Wang and Guoyao Wu. A Deficiency or Excess of Dietary Threonine Reduces Protein Synthesis in Jejunum and Skeletal Muscle of Young Pigs. June 2007, The Journal of Nutrition. Vol. 137, 1442 – 1446.

4. Threonine content in food. USDA National Nutrient Database for Standard Reference, Release 19 (2006).