Millions of people work out every day to lose weight, often eating a low-carb diet along the way. Others train to build muscle so they can better compete in athletic endeavors. But when people try to do these things at the same time, they can struggle.

"It's not optimal," says Jeff Hampl of Arizona State University's Department of Nutrition. "Someone on a low-carb diet is trying to lose body fat," he says. "Someone who is actively training and preparing for an event is trying to build muscle. "They're somewhat conflicting goals."

"It's almost like, why do they bother?" agrees Kim Hohol, who works in diabetes education and nutrition services for CIGNA. "You cannot be an athlete performing at your optimal level when you have a trainer telling you to do low carbs," she says. Many people believe that eating protein is the key to building muscle. But Hohol points out that, "Protein doesn't make muscle. Calories do. Those calories have to come from protein, carbs and fat. It has to be a combination."

In fact, she suggests that people load up on carbs — which can include starches, fruit and milk — starting about 72 hours before a competition. One study indicates a person on a high-carb diet can maintain a maximum performance level about three times longer than someone on a high-protein diet, she said.

Hampl and Hohol say carbs produce glycogen, or stored glucose, which in turn, gives the body energy. For the most part, people who are training would want "more glycogen in their muscle cells because it serves as an energy source," Hampl says.

Also backing this notion is Renae Cunnien, who manages the obesity prevention program for the state's Department of Health Services. "Carbohydrates in your diet provide energy," she says. "And you need energy for any activity that requires endurance." Otherwise, "You won't have enough energy to be able to build muscle." People who are trying to lose weight with a low-carb diet while trying to exercise may succeed for a while, "But you'll feel like crap doing it." In this situation, an exerciser may experience "bonking," when you "hit the wall and deplete your energy system."

"You say, 'I'm not going to do this today. I just don't feel like it.'"
"You're tired and fatigued. You burn out."
"It's like emptying your gas tank and you can't go any more."

So, what to do if losing weight is your main goal?

Boring as it sounds, Cunnien gives that age-old advice: "The best way to lose weight is to increase your activity and decrease your intake." For people who are actively exercising, she suggests a diet whose caloric content is 40 percent carbs, 40 percent protein and 20 percent fat.

Most people, of course, aren't going to measure calories precisely, let alone the percentage of calories by food group. But many figure all the exercise at least will point them in the right direction when it comes to diet. Take Stephanie Wyatt of Scottsdale. She regularly attends an exercise regimen run by Cunnien at Gold's Gym in north Scottsdale called a "muscle class." Says Wyatt, "I understand the concept. I've had friends who are trainers say, 'The best way to train is off carbs.' But I don't eat a pasta meal before or after workouts." Then again, she didn't head out to chow down on fast food after finishing a recent workout, either. Exercising regularly makes her want to eat healthier. "I just prefer well-balance meals."

Healthy Eating
Recommended percent of diet for those who exercise moderately:

• Fats: 20 percent
• Carbs: 40 percent
• Protein: 40 percent

Source: Renae Cunnien, Arizona Department of Health Services program manager for obesity prevention. Contact Mike Tulumello by email, or phone (480) 898-6525

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