Red kidney beans are a good source of plant-based protein, fiber, and various essential minerals. A 1/2 cup serving of red kidney beans (cooked) provides approximately 105 calories, 7 grams of protein, 1 gram of fat, 19 grams of carbohydrates, and 7 grams of fiber. These beans are also a good source of iron, folate, potassium, and other vitamins and minerals.