One-fourth of your plate should be made up of a healthy, lean protein, according to Christy L. Alexon, PhD, RD, a clinical associate professor at Arizona State University in Tempe, AZ, because it is the best source of energy.
Alexon has an easy trick for figuring out what a lean protein is. "I like to say the fewer legs, the better. Following that rule, fish would be the best, followed by a soy product or beans. Chicken breasts are OK as well — you know, two legs — but beef should be limited," she says. If you must do beef, she recommends grass-fed as a slightly better option, but any four-legged source is not your healthiest option to eat on a regular basis.