Beans are rich sources of fiber, protein and carbohydrates. These are one of the best calorie-dense foods that helps put on weight. Beans can be eaten as a snack or can be included in breakfast, lunch or dinner. There are several varieties of beans like red beans, black beans, soy beans, lima beans, lentils, and kidney beans. Alternatively, you can also prepare bean soup or bean salad. For quick results, eat them daily for one or two months.