Lentils are tiny nutritional powerhouses that offer a variety of health benefits. They are often star players in a balanced vegetarian diet. While lentils do contain all nine essential amino acids that are required by humans, they are low in the amino acid methionine, so you should not rely on them as your sole source of protein. When lentils are consumed along with other plant foods that are rich in methionine, you'll get the right amounts of all of the amino acids that your body needs.
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Understanding Amino Acids
Protein accounts for about 16.6 percent of your total weight -- only the water in your body weighs more. Protein is an important component of every cell. When you eat protein from plant or animal foods, your digestive system breaks it down into smaller molecules called amino acids. Your DNA then tells your cells how to put the amino acids back together in the right order to create muscles, blood, hormones, enzymes, bones and other body structures. Amino acids string together to form proteins much like letters combine to form words. The specific sequence of amino acids in a protein determines its shape and function.
Essential Vs. Non-Essential
There are 20 different amino acids that make up the various proteins of the human body. Your body can manufacture some of them from other amino acids, but the nine "essential" amino acids have to come from your diet. They are valine, leucine, isoleucine, methionine, phenylalanine, tryptophan, lysine, threonine and histidine. If your diet is missing or low in any one of the nine, you can experience health problems such as difficulty healing and susceptibility to infections.
Amino Acids in Lentils
Lentils are small, round, multicolored beans that have been used in traditional cuisines for centuries. According to the USDA's Food Nutrient Database, lentils contain over 50 percent of the daily value for the majority of the nine essential amino acids, but they only have about 0.15 grams of methionine per 1-cup serving. This is similar to the amino acid profile for other legumes such as kidney beans or black beans. Methionine is considered the "limiting" amino acid in lentils because once it has been used up, your body can't access the rest of the amino acids in the lentils you eat to make new tissues. This is the reason that, like other plant foods, lentils are regarded as a "low biological value" source of protein.
Lentils and other legumes are potent protectors from cardiovascular disease, thanks to their fiber, magnesium and homocysteine-lowering folate content. They are also naturally low in fat and calories. When you pair lentils with a methionine-rich plant food, such as whole-grain rice, you end up with a full spectrum of amino acids that's equivalent to a complete protein source. Other plant-protein combinations include legumes with seeds and grains with dairy -- these are commonly referred to as "complementary" proteins. As long as you combine enough complementary plant proteins throughout the course of a day (about 0.8 grams of protein per kilogram of your body weight is recommended), you'll be consuming enough essential amino acids to maintain your health.