Energy MetabolismOf the 20 amino acids required for protein synthesis, six of them (arginine, cysteine, glutamine, leucine, proline, and tryptophan), collectively known as the functional amino acids, regulate key metabolic pathways involved in cellular growth, and development, as well as other important biological processes such as immunity and reproduction.

Intense exercise decreases the plasma glutamine concentration and this may be related to immunosuppression.
Several researches found the efficacy of L-arginine and nitric oxide on penile erection, fixing erectile dysfunction.

For example, leucine activates mTOR signaling and increases protein synthesis, leading to lymphocyte proliferation. Therefore, a lack of leucine can compromise immune function. Metabolic pathways interrelated with the biosynthesis and degradation of these amino acids include vitamin and cofactor biosynthesis (such as SAM or S-Adenosyl Methionine) as well as neurotransmitter metabolism (such as glutamate).

Leucine food sources Leucine content (grams/ 100 gram food)
Soybeans, mature seeds, raw 2.97
lentils, raw 2.03
cowpea, catjang, mature seeds, raw 1.83
Beef, round, top round, separable lean and fat, trimmed to 1/8″ fat, select, raw 1.76
Beef, top sirloin, separable lean only, trimmed to 1/8″ fat, choice, raw 1.74
Peanuts, all types, raw 1.67
Salami, Italian, pork 1.63
Fish, salmon, pink, raw
Crustaceans, shrimp, mixed species, raw 1.61
Chicken, broilers or fryers, thigh, meat only, raw 1.48
Nuts, almonds 1.47
Egg, yolk, raw, fresh 1.40
Chickpeas (garbanzo beans, bengal gram), mature seeds, raw 1.37
Seeds, sesame butter, tahini, from raw and stone ground kernels 1.36
Chicken, broilers or fryers, wing, meat and skin, raw 1.29
flax seed, raw
Nuts, walnuts, english 1.17
Egg, whole, raw, fresh 1.09
Egg, white, raw, fresh 1.02
Sausage, Italian, pork, raw 0.96
Milk, sheep, fluid 0.59
Pork, fresh, separable fat, raw 0.40
Hummus 0.35
Milk, goat, fluid 0.31
Milk, whole, 3.25% milkfat 0.27
Soy milk, fluid 0.24
asparagus 0.13
Snap beans, green, raw 0.11
Milk, human, mature, fluid 0.10

Amino Acid L-Arginine, Nitric Oxide, and Erectile Dysfunction
Last Updated on Thursday, 05 April 2012 15:20
According to the National Health Institute (NIH) Consensus Development Panel on Impotence, erectile dysfunction (ED) is defined as the persistent inability to achieve and/or maintain an erection sufficient for satisfactory sexual performance.
Causes of erectile dysfunction may be psychological and physiological factors (neurogenic, vascular, endocrine causes). It may also be a side effect of drugs and a symptom of health complications such as diabetes.
Penile erection occurs as a result of increased blood inflow to the penis, engorgement with blood, and decreased outflow of blood from the penis. Primarily, this process is mediated by nitric oxide, which is a neurotransmitter and vasodilator. Nitric oxide is synthesized from L-arginine.

Several researches on the efficacy of L-arginine and nitric oxide on penile erection, fixing erectile dysfunction, have reported positive effects of both chemicals in stimulating and maintaining erection. For example, a study reported that 80 % of men (out of 40, age group 25 – 45) with erectile dysfunction treated with L-arginine (dosage: 1.7 g/ day) and Pycnogenol, an extract from French maritime pine bark (Pinus pinaster), (dosage: 80 mg/day) recovered from their erectile dysfunction after one month of treatment. Pycnogenol, also an antioxidant, stimulates synthesis of nitric oxide from L-arginine. The researchers reported that there was no side effect associated with the supplements.

In another double-blind, placebo-controlled, clinical research on the effect and safety of the combination of 6 g of L-arginine glutamate and 6 mg of yohimbine hydrochloride with that of 6 mg of yohimbine hydrochloride alone and that of placebo alone, for the treatment of erectile dysfunction (ED), it was reported that combined oral administration of the L-arginine glutamate ( 6 g) and yohimbine (6 mg) was effective in improving erectile function in patients with mild to moderate erectile dysfunction (ED).

Herbs and sexuality:
Yohimbe: health benefits and side effects
Ginseng: health benefits and side effects
Ginkgo Biloba: health benefits and side effects

Erectile dysfunction related articles:
What is erectile dysfunction? How does erection occur?
What are the causes of erectile dysfunction?
What are the treatments for erectile dysfunction?


Stanislavov, R. and Nikolova. 2003. Treatment of Erectile Dysfunction with Pycnogenol and L-arginine. Journal of Sex and Marital Therapy, 29(3): 207 – 213.

Basu, A. and Ryder, R. E. J. 2004. New Treatment Options for Erectile Dysfunction in Patients with Diabetes Mellitus. Drugs, 64(23): 2667 – 2688.

Toda, N. Ayajiki, K. Okamura, T. 2005. Nitric Oxide and Penile Erectile Function. Pharmacology and Therapeutics, 106: 233 – 266.

Lebret, T., Hervéa, J. M., Gornyb, P., Worcelc, M. and Botto, H. 2002. Efficacy and Safety of a Novel Combination of L-Arginine Glutamate and Yohimbine Hydrochloride: A New Oral Therapy for Erectile Dysfunction. European Urology 41(6): 608-613.

Functions of non-essential amino acids

The following list includse the 12 non-essential amino acids. Included is a some of the functions and benefits and side effects (if any) of the amino acids.

Alanine: Removes toxic substances released from breakdown of muscle protein during intensive exercise. Side effects: Excessive alanine level in the body is associated with chronic fatigue.
Cysteine: Component of protein type abundant in nails, skin and hair. It acts as antioxidant (free radical scavenger), and has synergetic effect when taken with other antioxidants such as vitamin E and selenium.
Cystine: The same as cysteine, it aids in removal of toxins and formation of skin.
Glutamine: Promotes healthy brain function. It is also necessary for the synthesis of RNA and DNA molecules.
Glutathione: Is antioxidant and has anti-aging effect. It is useful in removal of toxins.
Glycine: Component of skin and is beneficial for wound healing. It acts as neurotransmitter. The side effect of high level glycine in the body is that it may cause fatigue.
Histidine: Important for the synthesis of red and white blood cells. It is a precursor for histamine which is good for sexual arousal. Improve blood flow. Side effects of high dosage of histidine include stress and anxiety.
Serine: Constituent of brain proteins and aids in the synthesis of immune system proteins. It is also good for muscle growth.
Taurine: Necessary for proper brain function and synthesis of amino acids. It is important in the assimilation of mineral nutrients such as magnesium, calcium and potassium.
Threonine: Balances protein level in the body. It promotes immune system. It is also beneficial for the synthesis of tooth enamel and collagen.
Asparagine: It helps promote equilibrium in the central nervous system—aids in balancing state of emotion.
Apartic acid: Enhances stamina, aids in removal of toxins and ammonia from the body, and beneficial in the synthesis of proteins involved in the immune system.
Proline: plays role in intracellular signalling.
L-arginine: plays role in blood vessel relaxation, stimulating and maintaining erection in men, production of ejaculate, and removal of excess ammonia from the body.

A list of sample of high or low protein food sources is below:
Protein food source Estimated protein content
½ cup tofu
14 g
½ cup legumes 7 g
2 ounce lean meat, fish, poultry 14 g
1-2 ounces of nuts 14 g
1 slice of bread 3 g
1 cup raw vegetables 2 g

Maintenance of Immunity
It is generally believed that moderate exercise enhances immunocompetence and is effective for the prevention of inflammatory diseases, infection, and cancer, while excessive physical activity leads to immunosuppression and an increase of inflammatory and allergic disorders.

Susceptibility to infections following excessive physical activity is ascribed to an increase in the production of immunosuppressive factors such as adrenocortical hormones and anti-inflammatory cytokines, leading to a decrease in the number and activity of circulating natural killer cells and T cells as well as a lower IgA concentration in the saliva.
Therefore, athletes performing high-intensity training are exposed to the risk of impaired immunocompetence. Intake of carbohydrates during prolonged exercise at submaximal intensity attenuates the increase of plasma cortisol and cytokine levels after exercise, which could lead to the inhibition of immunosuppression.
Vitamin C and vitamin E have actions that promote immunity, and are essential for T cell differentiation and for maintenance of T cell function.
However, there is limited evidence about the effects of vitamins supplementation on immune function in relation to exercise.
Glutamine is an important energy source for lymphocytes, macrophages, and neutrophils, and is also an essential amino acid for the differentiation and growth of these cells.
Intense exercise decreases the plasma glutamine concentration and this may be related to immunosuppression.
Castell et al. reported that athletes who ingested glutamine had a lower infection rate after a marathon compared with the placebo group. They also demonstrated that intake of glutamine resulted in an increase of the T-helper/T-suppressor cell ratio.
Furthermore, glutamine enhances the activity of intestinal enterobacteria and inhibits the production of cytokines involved in inflammation or immunosuppression.
Due to a social background that includes changes of dietary habits, an aging population, and increased medical costs, people have shown a growing interest in health and have come to expect complex and diverse actions of foods.
In recent years, various food factors that fulfill such requirements have been evaluated scientifically to determine whether they are any physiological effects like prevention of diseases.

In the sports market, a variety of functional foods are available, but among these functional foods, some have not clearly demonstrated any efficacy and others are advertised with inappropriate and exaggerated claims, so consumers are often confused. Some of the food components described in this article should be studied further because of differing views with regard to their efficacy in different reports.

Furthermore, the effectiveness of the components may differ according to gender, between individuals, and with the mode of ingestion, so that the optimum method of intake the quantity and quality of foods to be ingested, and the timing of their intake need to be established in accordance with the purpose of using each food or food component, after understanding the physiological changes by exercise.

In the future, guidelines for the use and evaluation system of sports functional foods should be established with backing by clear scientific evidence related to the individual foods.
Wataru Aoi1 ,2 , Yuji Naito3 and Toshikazu Yoshikawa2 ,3
1Research Center for Sports Medicine, Doshisha University, Kyoto 602-8580, Japan
2Department of Inflammation and Immunology, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan
3Department of Medical Proteomics, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan

Nutrition Journal 2006, 5:15 doi:10.1186/1475-2891-5-15