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Your body type in a nutshell: You're naturally lean and have trouble putting weight on. You may also be thin but carry a lot of fat (aka "skinny fat").

Your ideal routine: One that embraces the unexpected. You may find you naturally gravitate toward endurance activities (like running), says Brian St. Pierre, MS, RD, CSCS, director of performance nutrition at Precision Nutrition. However, that may mean you're missing out on essential strength-building workouts. For a well-rounded routine, add in plyometrics (jumping lunges, squat jumps, box jumps) or weight-based exercises, recommends Stacy Sims, PhD, exercise physiologist and nutrition scientist, author of ROAR: How to Match Your Food and Fitness to Your Female Physiology for Optimum Performance, Great Health, and a Strong, Lean Body for Life.

Since you have a fast metabolism, your body can handle a greater amount of carbs—lucky you—but you'll want to focus on wholesome, fiber-rich carbs, which give you lasting energy. Try a sweet potato (rich in complex carbohydrates) topped with a bit of almond butter for satiating fat (seriously, try it), a hardboiled egg (for some protein) and fruit (more carbs!).