It's not only high in muscle-building amino acids, it's also a powerhouse of iron and zinc, which aid circulatory health. In fact, beef is so nutrient-dense that a three-ounce serving supplies more than 10% of your recommended daily intake of a number of nutrients, including protein, B6 and B12, selenium, phosphorus, niacin, and riboflavin. Worried about the fat? Don't. According to USDA data, today's beef is up to 20% leaner than it was a decade ago. In fact, 19 cuts of beef meet government guidelines as being a lean meat. To keep the meat you're buying lean as well as tender and flavorful, opt for cuts with the words round or top in the name-things like eye round roast, top round, or top sirloin steak.