Lentils are mentioned often as a good source of protein. Are all types of lentils, like green, brown and red, equally good sources of protein, or are there significant differences?
A search of the USDA nutrient database gives us a few entries to compare:
Note that some of these are "product" profiles, so they may have other ingredients added (spices, etc.) which could affect the protein percentage.
This study came up with a slightly higher average than our above USDA stats would suggest (emphasis mine):
Chemical and amino acid compositions, protein solubility (Osborn classification), and in vitro protein quality of six genotypes of lentils (Lens culinaris Medik.) were determined. Lentils contained an average of 28.6% protein, 3.1% ash, 4.4% fiber, 0.7% ether extract, 63.1% total carbohydrate (nitrogen-free extract), 44.3% starch and 4,186 kcal/kg of gross energy.
And regarding amino acid composition (from the abstract of the same study):
The amino acid compositions of the six lentil genotypes were similar. The major amino acids were glutamic acid, aspartic acid, arginine, leucine and lysine; the minor amino acids were methionine, cystine and tryptophan.
Lentils are almost complete proteins, and you'll get the extra methionine/cystine and tryptophan from other foods in your diet (like rice).
So, yes, all common lentil varieties appear to be great sources of protein. Hope that helps!
Based on the USDA (United States Department of Agriculture) food database (1 2), the standard reference for food comparison, there are small differences in the amount of proteins of several varieties of lentils. However, the differences are quite small, being the standard error 0,27 for the first source and 0,7 for the second, so we can consider lentils good sources of proteins.
The variations are due to several factors: cultivar (green, brown, red lentils, etc.) and the conditions of the field where the vegetable produce was made (fertility, micronutrients, etc.)