Amino Acid rich food is important for building muscle and maintaining normal metabolic function in the body. Protein is made of amino acids, so the best place to find aminos is in protein rich food.
Amino Acids in Food
The human body requires 22 amino acids make protein and correctly function. Of these, nine are classed "essential", as they cannot be made by the body and must be taken in through the diet. In addition, the body is only able to produce some aminos in smaller amounts – these amino acids are known as "conditionally essential"
Proteins are present in animals, plants and simple organisms. Different types of food contain different types of proteins, and each different type of protein contains amino acids in differing proportions. The nutritional quality of the protein in food is defined by how closely the amino acid profile reflects human dietary requirements, and how digestible the protein is by the body.
On top of this, some foods are richer in protein than others, for example, meat contains more protein than vegetables. The type, usability, digestibility, and amount of protein are all important considerations when assessing the amino acids in various foods (1).
Amino Acids in Plants
Plant foods, including cereal crops and legumes, are important sources of protein for many people. While plants form a wide and varied class of food, there are some features that are common to plant proteins.
Plant proteins, moreso than proteins of animal origin, have the tendency to be deficient in certain essential amino acids, most commonly lysine and methionine, although not all plant protein is identical, and rice and beans are good sources of methionine and lysine respectively (2). Plant foods are generally high in non-essential amino acids arginine, glycine, alanine and serine.
Plant protein is generally less digestible than protein derived from animals. This may be due to a number of factors, including high levels of insoluble fibre and antinutritional factors, which are chemicals that can prevent the breakdown and use of various components in food. An example of this is soybean trypsin inhibitor, which as the name suggests, is a chemical found in soybeans that inhibits the action of trypsin, which is an enzyme produced in the digestive system that breaks protein down into amino acids (3).
In spite of these negatives, plant protein can still be an excellent source of protein. Many of the factors that contribute to poor digestibility can be removed through processing. Additionally, eating a diet rich in plant proteins has been shown to reduce the accumulation of fat, and enhance insulin sensitivity, partially as a consequence of the amino acid profile (4).
Amino Acids in Milk
Milk is made up of two of the best known proteins in the sports nutrition world, whey and casein. These two proteins are widely used in supplements because of their complete amino acid profiles and easy digestibility.
The two proteins have different properties, most notably speed of digestion, but they are quite similar in their amino acid profiles and are both high in branched chain amino acids, Leucine, Isoleucine and Valine, which are known for their prominent role in muscle building (5).
Amino Acids in Oats
Groats, or hulled wholegrain oat kernels contain on average 17% protein. Oat protein is considered to be "complete", containing all the amino acids, but like many other plants, oats are low in some vital amino acids, particularly lysine (6). Nonetheless, oats are one of the best plant protein sources available, containing both higher proportion and quality of protein than most other grains.
Oats are very high in glutamic acid, which is important for digestive health, and acts as a precursor to glutamine, an important amino acid for athletes, because it prevents catabolism and boosts immune health.
(1) Tome D. Criteria and markers for protein quality assessment - a review. Br J Nutr. 2012 Aug;108 Suppl 2:S222-9.
(2) Galili G1, Amir R Fortifying plants with the essential amino acids lysine and methionine to improve nutritional quality. Plant Biotechnol J. 2013 Feb;11(2):211-22.
(3) Sarwar Gilani G1, Wu Xiao C, Cockell KA. Impact of antinutritional factors in food proteins on the digestibility of protein and the bioavailability of amino acids and on protein quality. Br J Nutr. 2012 Aug;108 Suppl 2:S315-32.
(4) Krajcovicova-Kudlackova M1, Babinska K, Valachovicova M. Health benefits and risks of plant proteins. Bratisl Lek Listy. 2005;106(6-7):231-4.
(5) National Dairy Council (2006) Emerging health benefits of dairy proteins. Dairy Council Digest. July/August, Vol. 77, No. 4.
(6) Pomerantz Y, Youngs VL, Robbins GS. Protein content and amino acid composition of Oat species and tissues. Agricultural Research Service, US Department of Agriculture, Madison Wisconsin (1973).