"Lean meat" is a misleading term. I noticed many times in conversations that people who think that they eat "proteins" tend to think about this food group as an almost pure protein, a perfect set of essential amino acids. Especially if they consume so called "lean meats."
In beef (presented as "90% lean meat") - half of the calories are from fat (http://nutritiondata.self.com/facts/beef-products/6193/2). Even in the leanest bird meat approximately the fifth of the energy is from fat, ~18% in the leanest I could find (http://nutritiondata.self.com/facts/poultry-products/704/2).
Digestibility-corrected amino acid score (PDCAAS) of protein in beef is only 0.92, chicken - 0.91(?), and egg whites and soy - 1 or 100% (not that it matters much). Note, that 62% of calories in a whole egg are from fat, and 40% in soybeans.
