a deck of cards

Go lean with protein. Protein is an important part of a balanced diet. Choose breast meat or low-fat ground chicken or turkey, and ground beef that is 90 percent lean or more. Limit meat and poultry servings to 3 ounces — about the size of a deck of cards. Don't eat meat? Lentils, plain Greek yogurt, eggs and nuts are great sources of protein, too. source