Beef is a major contributor of protein, zinc and vitamin B12, vitamin B6, iron and niacin. By supplying a nutrient bundle in every bite, eating beef is a great way to make the most of your calories. A 3 oz. serving of lean beef contributes less than 10% of the calories in a 2,000-calorie diet. At the same time, it supplies more than 10% of the Daily Value for these nutrients.