Protein is the building block for muscle repair, and a necessary component of a diet to support strength-building exercise. However, eating loads of protein alone does not improve muscle strength. Meat delivers a lot of protein in a small serving, but it also includes unhealthy saturated fats. Beans cooked in soups, casseroles or blended and served as hummus, bean dip or a sandwich spread provide protein, along with fiber, vitamins and minerals.
Iron carries oxygen to muscle cells, helping them function, repair and grow. Iron depletion can occur at the beginning of a strength training regimen, leading to exhaustion, according to Christopher Newton University. Dark leafy greens such as spinach, wild bitter greens such as nettle and dandelion, and the herb parsley are high in iron content. The vitamin C in these plants helps makes the iron easier to absorb, and unlike red meat sources of iron, these natural plants and herbs are low in calories and fat.
Carbohydrates provide the fuel muscles need to function efficiently. Adults who are strength training should take in about half their daily calories as carbs, according to the American Dietetic Association. Whole grains such as brown rice, oatmeal and whole-grain breads are the best sources of complex carbs that will provide a slow, steady fuel supply to muscles, along with a wealth of vitamins and minerals. For a low-calorie, high-carb, whole-grain snack, try popcorn: Three cups of air-popped corn supply a single serving of carbs to fuel muscles with no fat and minimal calories.
Fat fuels muscles when they are under stress, such as during strength training exercises. Fats are calorie-dense, and fats from meat sources or hydrogenated oils can lead to cardiovascular health problems. About 35 percent of daily calories for people doing strength training should come from healthy fats such as walnuts, pistachios and almonds, according to the American Dietetic Association. In addition to bolstering muscle strength, eating nuts regularly can decrease risk of heart disease, according to the Iowa State University Extension.