Cool study: http://rsbl.royalsocietypublishing.org/content/early/2011/05/30/rsbl.2011.0321
About the study:
"What's interesting is that the seasonal switch between the two food types closely mirrors two views on human nutrition. During the heavy fruit season, the gorillas eat up to 40% of their diet of pieces of fruit, and 16% of their energy from protein — which matches what most humans like, and the recommendations for protein levels given by the America Heart Association. Conversely, during the winter when fruit can't be easily found, they switch to a protein heavy diet, where protein accounts for some 30% of their daily energy — which is what people who try to lose weight with high protein diets strive for."