It also occurred to me to check into this claim on the amino acid profile of quinoa.
Here are the facts, using data from the USDA Nutrient Database. The table compares quinoa, eggs, milk, and top sirloin broiled
– in that order – for amino acid content per 100 g protein content.
While quinoa does have all the essential amino acids in reasonable quantity, actually it is not as rich in them as sources such as eggs, milk, or beef.
So not only is it low in protein percentage-wise, but you’d need a greater quantity of quinoa protein to be equal to common bodybuilding protein sources.
Tryptophan 1.2, 1.3, 2.3, 0.7
Threonine 3.0, 4.4, 4.4, 4.0
Isoleucine 3.6, 5.3, 5.1, 4.5
Leucine 6.0, 8.7, 8.2, 8.0
Lysine 5.5, 7.3, 4.3, 8.5
Methionine 2.2, 3.0, 2.3, 2.6
Cystine 1.4, 2.2, 2.3, 1.3
Phenylalanine 4.2, 5.4, 4.6, 3.9
Tyrosine 1.9, 4.0, 4.7, 3.2
Valine 4.2, 6.8, 9.0, 5.0
Arginine 7.8, 6.5, 2.3, 6.5
Histidine 2.9, 2.5, 2.3, 3.2
Alanine 4.2, 5.9, 3.2, 6.1
Aspartic acid 8.0, 10.6, 7.4, 9.1
Glutamic acid 13.2, 13.3, 20.1, 15.0
Glycine 4.9, 3.4, 2.3, 6.1
Proline 5.5, 4.0, 10.6, 4.8
Serine 4.0, 7.7, 3.3, 3.9