Protein quantity plant-based diets is shown not to be an issue. Inadequate amino acid supply is not an issue with most cereal-based diets.

When used to score plant-based diets in India, no marked deficiencies are identified. All regions score > 1 for adults, whilst for children scores range from > 1, (Tamil Nadhu) from 6 months of age to 0.78 (West Bengal), rising to 0.9 in the 2-5 year old, consistent with reports that high-lysine maize supports similar weight and height growth to that of casein. 

Digestibility is identified as a problem for some cereals (millet (Panicum miliaceum) and sorghum (Sorghum sp.)) and generally is poorly understood.

A new maintenance requirement pattern is developed, with higher values than those of Food and Agriculture Organization / World Health Organization / United Nations University (1985) but lower values than the Massachusetts Institute of Technology pattern (Young et al. 1989).

Calculations of age-related amino acid requirements are based on most recent estimates of human growth and maintenance protein requirements, a tissue amino acid pattern and the new maintenance amino acid pattern. These values appear valid when used to score plant proteins, since they indicate values similar to or less than the biological value measured directly in young children.

Estimated Average Requirement (EAR) and Recommended Dietary Allowance (RDA) for amino acids (protein) for healthy adults 19 y and older, mg/kg/day:

• Estimated Average Requirement (EAR): average, estimated to meet the requirements of 50%.
• Recommended Dietary Allowance (RDA): average, sufficient to meet the nutrient requirements of nearly all.

Estimates of Amino Acid Requirements for adults, mg / kg per day

• Phenylalanine + tyrosine: 14
• Leucine: 14
• Methionine + cystine: 13
• Histidine: 8–12
• Lysine: 12
• Isoleucine: 10
• Valine: 10
• Threonine: 7
• Tryptophan: 3.5

An essential amino acid, or indispensable amino acid, is an amino acid that cannot be synthesized by the organism, and must be supplied in diet. 

The 9 amino acids humans cannot synthesize (F V T W M L I K H):

• phenylalanine
• valine
• threonine
• tryptophan
• methionine
• leucine
• isoleucine
• lysine
• histidine

Animal and plant proteins are made up of about 20 common amino acids.

Synthesis of 6 other amino acids - conditionally essential - can be limited under special conditions (R C G Q P Y): arginine, cysteine, glycine, glutamine, proline, and tyrosine.

Dispensable amino acids can be synthesized in the human body, 5 (A D N E S): alanine, aspartic acid, asparagine, glutamic acid and serine .