Beef is rich in choline, iron, magnesium, niacin, phosphorus, potassium, protein, vitamin B6, vitamin B12, and zinc. Beef liver is rich in choline, iodine, iron, niacin, protein, vitamin B6, vitamin B12, and vitamin A, vitamin D, vitamin K, and zinc. Beef broth, beef sausage, ground beef, pot roast, and slow-cooked tough cuts of meat are rich in glycine.