While the exact level varies depending on the type of lentil, the average cup contains nearly 18 grams of protein - making them the more protein-rich legume compared to chickpeas. In fact, lentils are typically made up of about 25% protein, which is the same composition as lean beef. They're also packed with iron, magnesium, and B vitamins. On top of all of that they contain fiber and, according to a 2017 study, are associated with lowering the risk of heart disease.