Of the top 10 sources of protein in the American diet, only two sources—yeast breads and pasta—are plant‐based. Lentils, a dense source of plant protein, don’t even make the list. Yet look at the comparison between the nutritional profile of lentils and the profile of beef in Table 1.
When we consider these two foods, it’s no contest. To reduce fat, saturated fat, and cholesterol while increasing fiber, the lentils win hands down! With all that lentils have going for them, you’d think more Americans would be eating them. Yet dried beans, peas, and lentils combined contribute less than 1 percent of the daily protein intake of Americans, while beef contributes 17.7 percent.
High‐protein plant foods also contribute complex carbohydrates, dietary fiber, and vitamins and minerals to the diet. Since these plant foods contain little fat, they are nutrient dense; that is, they provide a high amount of protein and nutrients relative to their energy contribution.
Sources of Plant Protein
Grains and grain products, legumes (lentils and dried beans and peas such as kidney beans or chickpeas), starchy vegetables, and nuts and seeds all provide protein (Table 2). A serving of a grain product or starchy vegetable provides an average of about 5 grams of protein, a serving of legumes provides 10 to 20 grams of protein, and a serving of vegetables provides about 3 grams of protein. Although a serving of these foods contains less protein than a serving of meat, you can eat more plant protein foods for fewer calories.
Complementing Plant Proteins
It’s important to remember that plant proteins lack one or more of the indispensable amino acids needed to build body proteins, so individual plant proteins need to complement each other. A simple rule to remember in complementing plant proteins is that combining grains and legumes or combining legumes and nuts or seeds provides complete, high‐quality protein.
The protein in soybeans is a notable exception to the rule that most plant proteins are incomplete. Soy provides complete, high‐quality protein comparable to that in animal foods. In addition, soybeans provide no saturated fat or cholesterol, and are rich in isoflavonoids—phytochemicals that help reduce risk of heart disease and cancer and improve bone health.
Isoflavonoids act as antioxidants, protecting cells and tissues from damage. One specific isoflavonoid, genistein, inhibits growth of both breast and prostate cancer cells in the laboratory. Isoflavonoids protect LDL cholesterol (the kind of cholesterol associated with greater risk of heart disease) from oxidation. Oxidized LDL cholesterol contributes to the plaque buildup in arteries. The isoflavones in soybeans also act as phytoestrogens, helping to protect older women from cardiovascular disease and osteoporosis. Soy foods that contain most or all of the bean, such as soy milk, sprouts, flour, and tofu, are the best sources of these phytochemicals.
It is easy to incorporate a variety of soy foods into your diet. Tofu, tempeh, ground soy, soy milk, soy flour, and textured soy protein are soy‐based products that can be included in many meals and snacks (Table 3).
The nutritional benefits of plant protein sources such as soy foods and other legumes, grains, and vegetables deserve a closer look. Most Americans would benefit from emphasizing plant protein foods in their diet. The next time you plan to make meat loaf, make lentil loaf instead.