Beans contain both starch and protein, making them a part of each group. When eating one serving of beans, it counts as both one serving of starch and one serving of protein. Starchy vegetables like beans are a benefit in any diet because they are low in fat and filling.
Beans contain a large amount of fiber, which is more slowly digested than other foods and helps to stave off hunger longer than other similar items like meat. Beans also contain phytochemicals such as antioxidants, which are functional in preventing damage from free radicals. Beans also contain a large amount of water.