Touted as one of the best athletic foods available by sports nutritionist and Registered Dietitian Nancy Clark, peanut butter offers modest amounts of protein as well as energy in the form of heart-healthy fats. It also provides your diet with magnesium, zinc, folate and vitamin E. The protein in peanut butter – approximately 7 g per 2 tbsp. – is not complete, however. In other words, it does not contain all the essential amino acids you need for optimal health.
Amino acids serve as the building blocks of protein in your diet. When you consume a protein-containing food, your digestive system breaks down the protein into its constituent amino acids. Your body then creates new proteins as needed from the pool of dietary amino acids. Of the 20 amino acids in the foods you eat, nine are essential to your diet because your body cannot synthesize them. If your diet lacks one or more of these, your body degrades your muscle tissue to obtain the missing amino acids. Peanut butter protein is a so-called incomplete protein, as it does not offer all the essential amino acids.
The nine essential amino acids are histidine, isoleucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Peanut butter is rich in leucine and phenylalanine, containing roughly 0.5 g and 0.4 g per 2 tbsp., respectively, according to the U.S. Department of Agriculture National Nutrient Database. Tyrosine, valine, lysine, isoleucine and threonine are present in moderate amounts, with 2 tbsp. of peanut butter providing between 160 and 260 mg of each. Histidine is the second-lowest essential amino acid in peanut butter, at 100 mg per 2 tbsp., while tryptophan is peanut butter’s limiting amino acid, present at less than 75 mg in 2 tbsp.
Although peanut butter does not contain enough of all the amino acids to qualify as a high-quality protein, you can combine it with other foods to create a nutritionally complete protein. For example, eating your peanut butter on whole wheat toast or combining it into smoothie with yogurt or powdered milk supplies your diet with the full complement of amino acids you need for optimal health. In fact, any legume in combination with a grain or a small amount of animal protein supplies your diet with essential amino acids.
Understanding the amino acid profile of peanut butter may help you design a healthy diet to meet your fitness needs. As a concentrated source of energy, peanut butter provides you with calories to fuel your activities and with some of the amino acids you need to build muscle and support your bodily functions. In addition, the protein and fat content of peanut butter helps you feel full for a longer period of time than foods with simple carbs.