Amino Acids

More Than Just Muscle Preservation

By Jason Barker, ND

The building blocks of protein, amino acids are ubiquitous throughout the body and maintain numerous roles. Amino acids are important to build the muscle mass that declines with age, to enhance recovery from exercise and to support proper immune health. In fact, exercise, aging, and illness all have one thing in common: they increase the body’s demand for essential and non-essential amino acids. While the muscles contain the richest storage of amino acids in the body, amino acids are also used prominently in brain metabolism, neurotransmission, gastrointestinal health, immune function and cardiovascular health. Amino acids can also contribute to energy production through their conversion into glucose via gluconeogenesis.

Amino acids are the basic building blocks of proteins; shorter amino acid chains are termed peptides and longer chains are termed polypeptides or proteins. A popular analogy is that amino acids can be thought of as letters which can be arranged in an infinite variety to form different words, the proteins.

Amino acids can be considered essential, non-essential or conditionally essential given the body’s ability to synthesize what it needs for metabolic maintenance. While hundreds of different amino acids exist in nature, there are only 20 main amino acids used for protein biosynthesis as directed by genetic coding; depending on the organism, certain amino acids can be synthesized and others (termed essential) must be derived from the diet. These amino acids are required daily due to the body’s relatively low storage capacity.

Dietary proteins are often referred to as either complete or incomplete; a complete protein contains at least all 9 essential amino acids while incomplete food proteins do not. Animal-based foodstuffs are typically considered complete proteins (meat, poultry, fish, milk and eggs) while plant foodstuffs (on an individual basis) are considered incomplete proteins. The one exception to this is soy, which contains all 9 essential amino acids. Otherwise, plant-based foodstuffs can be combined to form complete proteins typically by combining grains, legumes or nuts/seeds in certain order.

Similar to other nutritional factors like vitamins and minerals, our body requires amino acids daily for optimal health and functioning. Although, like vitamins and minerals, basic amounts can be found in most healthy diets, increased intake of amino acids can also be employed for a variety of reasons. Modern medicine continues to develop a growing appreciation for the role that amino acids play in health and the consequences of their imbalance are continuously explored in research. What follows is a description of the many ways amino acid supplementation can improve health.

Maintaining Muscle Mass

Amino acids comprising a high quality complete protein serve as the primary building block of the body’s muscle mass, regardless of age. Athletes and individuals over 50 are two different populations that require a complete amino acid source for similar reasons, but with different causes. In athletes, this population typically requires additional amino acids for two main reasons. The first need is during times of aerobic exercise. Intense aerobic fitness that lasts more than an hour will cause the body to shift to protein catabolism as a source of additional fuel when immediate sources of energy (blood sugar) begins to decline.¹ This typically occurs when glycogen (carbohydrate-based) energy stores become depleted.² Once low glycogen store signals are received by the body, it will begin a catabolic, or degenerative process of stripping amino acids out of the muscles for gluconeogenesis, where the body makes glucose (its primary fuel source) from amino acids.^3-4 All of this comes at a very expensive metabolic cost, as the energy required to build muscle (protein) is very great, which is then broken down for fuel during intense aerobic exercise. Replacement of amino acids in the form of a complete protein both prior to and following exercise has been shown to prevent and ameliorate exercise-induced muscle damage, thereby improving recovery time.⁵

The second main area for amino acid replacement occurs primarily in anaerobic regimens such as weight training. Muscles that are stressed from weight training are also broken down, but because of physical stress rather than for energy production. Regardless, the needs of the muscle are the same; amino acids must be replaced in order for adequate muscle repair to occur.

Furthermore, newer research has shown that endurance performance is extended when amino acids (protein) are consumed during prolonged aerobic exercise bouts.⁶ In one study, athletes fed a protein-rich recovery meal demonstrated a 25 percent higher testosterone level, reduced plasma creatine kinase (a marker of muscle damage), and decreased fatigue and leg soreness compared to a group using only carbohydrate-based recovery meals.⁷ Newer evidence continues to emerge that is leading to a shift in the prior rule that only carbohydrate supplementation was beneficial for exercise performance; more studies are looking at how protein-carbohydrate combinations affect athletic performance.

Age-Related Muscle Loss

Another population that benefits from amino acid supplementation is the aging. Sarcopenia is a condition that is defined as age-related loss of muscle mass that usually occurs after the age of 50. It is marked by replacement of muscle fibers with fat and connective tissue. Most people don’t notice the beginnings of this process for many years or even decades. However, once symptomatic, a notable loss of strength, flexibility and the ability to repair after injury occur. Further, loss of skeletal muscle contributes to an increased risk of falls, fractures and eventual loss of independence.⁸

Maintaining muscle health in this population is similar to that in athletic individuals; adequate amino acids comprising complete protein are needed in order to supply the muscle with its building blocks for repair and regeneration. Amino Acids, along with other nutritional factors, have been shown to greatly improve the sarcopenic condition in human subjects by increasing lean body mass.^9-10

Immune System Function

The immune system is a highly complicated, intricate network that in some cases can be easily enhanced to improve function. For instance, two major immune cells, lymphocytes and macrophages, consume the amino acid glutamine at a high rate.¹¹ Because of this relationship, overuse of the muscles contributes to decreased lymphocyte function due to the overall protein and amino acid loss in such exercise bouts. The “glutamine hypothesis” states that in times of intense and prolonged physical stress, the demand for glutamine in muscle cells and other organs leaves the body in a state of relative glutamine scarcity.^12-13 When supplemented with glutamine, endurance athletes reported significant reductions in illness.¹⁴ Some evidence points to improved neutrophil function as a benefit of glutamine supplementation.¹⁵ Other immune-related conditions in which glutamine has been studied include radiation-induced oral mucositis and HIV.^16-17

Another amino acid, arginine, is useful for suboptimal immune responses and can reduce the occurrence of post-surgical infections. Arginine performs this task by lowering the amount of cell adhesion molecules in native cells (thereby thwarting viral and bacterial entry) and by lowering pro-inflammatory cytokines. Arginine was shown to increase the activity of natural killer cell activity, lymphocyte reactivity, and lymphocyte activation of natural killer cells in patients with breast cancer.¹⁸

Conclusion

The use of amino acids is an emerging science with the most prominent areas of research existing around athletic dietary performance, muscle building in the aging population and immune function. On a broader scale, obtaining a complete amino acid intake is needed for so many of the body’s basic needs, similar to a daily multivitamin and mineral, that virtually anyone can benefit from an increased intake.

References

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9. Solerte SB, Gazzaruso C, Bonacasa R, Rondanelli M, Zamboni M, Basso C, Locatelli E, Schifino N, Giustina A, Fioravanti M. Nutritional supplements with oral amino acid mixtures increases whole-body lean mass and insulin sensitivity in elderly subjects with sarcopenia. Am J Cardiol. 2008 Jun 2;101(11A):69E-77E.

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11. Newsholme EA, Parry Billings M. Properties of glutamine release from muscle and its importance for the immune system. J Parenteral Enteral Nutr. 1990;14 Suppl: 63S-67S.

12. Keast D, Arstein D, Harper W, Fry RW, Morton AR. Depression of plasma glutamine concentration after exercise stress and its possible influence on the immune system. Med J Aust. 1995;162: 15-18.

13. Rowbottom DG, Keast D, and Morton AR. The emerging role of glutamine as an indicator of exercise stress and overtraining. Sports Med. 1996;21: 80-97.

14. Castell L. Glutamine supplementation in vitro and in vivo, in exercise and in immunodepression. Sports Med. 2003;33(5):323-45.

15. Castell LM. Can glutamine modify the apparent immunodepression observed after prolonged, exhaustive exercise? Nutrition. 2002 May;18(5):371-5.

16. Rubio IT, Cao Y, Hutchins LF. Effect of glutamine on methotrexate efficacy and toxicity. Ann Surg. 1998;227:772-8.

17. Shabert JK, Winslow C, Lacey JM, Wilmore DW. Glutamine-antioxidant supplementation increases body cell mass in AIDS patients with weight loss: a randomized, double-blind controlled trial. Nutrition. 1999;15:860-4.

18. Brittenden J, Park KGM, Heys SD, et al. Larginine stimulates host defenses in patients with breast cancer. Surgery. 1994;115:205-212.

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