Peanuts are a rich source of protein (roughly 30 grams per cup after roasting). Prior to 1990 the PER method of protein evaluation considered peanut protein along with soy protein an incomplete protein, containing relatively low amounts of the essential amino acids, cystine, and methionine (but high in lysine), and it was advised to be sure that a diet or meal with peanuts as a staple also include complementary foods such as whole grains like corn and wheat, which are adequate in methionine but limited by lysine. Protein combining has been largely discredited. Since 1990 the gold standard for measuring protein quality is the Protein Digestibility Corrected Amino Acid Score (PDCAAS) and by this criterion peanut protein and other legume proteins such as soy protein is the nutritional equivalent of meat and eggs for human growth and health. An example of an extremely nutritious peanut-based food to restore health in starving-malnourished children is Plumpy'nut.
Peanut oil is a mainly monounsaturated fat, much of which is oleic acid, the healthful type of fat that has been implicated for skin health. Some say peanuts are an unbalanced source of fat because they have only trace amounts of required Omega-3 fats. Some brands of peanut butter are fortified with Omega-3 in the form of flaxseed oil to balance the ratio of Omega-3 to Omega-6.