David L. Katz, MD
Photo: Mackenzie Stroh
Q: I'm following a food plan that has me eating fruit, vegetables, protein, and plant oils. I love to work out, and I feel a bit weak at times. Do I need to eat more carbohydrates for energy? Or just different kinds of fruits and veggies?
— Lara Wessel, Miami

A. Your body is efficient at using calories from just about any source. We can, for example, make glucose—the energy our cells need to function—from protein, fat, or carbohydrates. I wonder whether you're eating enough, though: If you work out regularly, your total calorie needs may be higher than you realize. Be sure to take in enough food to maintain your desired weight; over time, that's a reliable indicator that you are getting the right amount of fuel. To find the actual number of calories your body requires, visit the energy needs calculator at the Baylor College of Medicine website (www.bcm.edu/cnrc/caloriesneed.htm).

Also, your diet sounds healthful but limited. There's a difference between putting enough fuel in the tank and putting in premium. To get all the nutrients you need, be sure to vary the fruits and vegetables you eat. In the protein category, emphasize fish, skinless poultry, lean meats, and nonfat dairy. And while produce provides some carbohydrates, you may in fact need more. Adding whole grains, beans, and lentils will provide zinc, B vitamins, and fiber—all useful for increasing your energy level.