Lamb is an excellent source of protein, 4 oz of lamb contains 27g of protein, or 55 percent of your RDA. Lamb also delivers vitamin B12, niacin and riboflavin. Vitamin B12 is essential for red blood cell production,nerve function and metabolism. Niacin, or vitamin B3, helps the body release energy from food and is important for nervous system function. Riboflavin, or vitamin B2, also helps the body release energy from foods and plays a role in good vision. Lamb is also a good source of zinc (33% of RDA). Zinc helps to maintains healthy testosterone levels.