Adults should eat at least 2 to 3 cups of vegetables per day, according to the USDA's ChooseMyPlate website. Vegetables consist mainly of carbohydrates, but most also contain at least small amounts of protein as well. Most Americans get plenty of protein through their diets, but if you are worried about your protein intake, dried beans and peas are among the best vegetable sources of this nutrient.

Beans and other legumes are such good sources of protein that you can count them toward either your recommended protein servings or your recommended vegetable servings. For example, a cup of canned navy beans has about 19.7 grams of protein and 53.6 grams of carbohydrates, and a cup of canned great northern beans has 19.3 grams of protein and 55.1 grams of carbohydrates. Other legumes with at least 15 grams of protein per cup include chickpeas, lentils, white beans, edamame, kidney beans, cranberry beans, split peas, pink beans and black beans.

Non-starchy vegetables are among the healthier vegetable choices because they provide high amounts of vitamins and minerals but contain only a small number of calories per serving. Canned straw mushrooms have 7 grams of protein and 8.4 grams of carbohydrates per cup. A cup of canned spinach has 6 grams of protein and 7.3 grams of carbohydrates. A cup of chopped broccoli has about 5.7 grams of protein and 9.8 grams of carbohydrates, and a cup of cooked frozen Brussels sprouts has 5.6 grams of protein and 12.9 grams of carbohydrates.

Some starchy vegetables also contain significant amounts of protein. A large baked Russet potato with the skin has 7.9 grams of protein and 64.1 grams of carbohydrates, and a cup of cooked sliced taro root has 5.7 grams of protein and 9.4 grams of carbohydrates. Eat a cup of corn, and you'll get 5.4 grams of protein and 38.8 grams of carbohydrates.

Although vegetables can have significant amounts of protein, soybeans are the only vegetable that contains all of the essential amino acids. Animal-based protein foods and quinoa also provide all of the essential amino acids. As long as you eat a variety of different protein-rich foods throughout the day, however, you'll get enough amino acids, even if you're vegetarian.