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Calorie Restriction: Can eating less lead to a longer life?

At first glance, Zac Culliton appears to be your average 30-year old. Newly married, working his job at a publishing company, and playing his bass guitar in a band on the weekends. But sit down for a meal with him, and you notice there's something different. He doesn't order a beer, a burger, or French fries like most men his age might. Zac's dinner is a small plain chicken breast, steamed vegetables, and water - not much for his 5'9" frame. Zac is on a calorie-restricted diet. He consumes between 1,500 and 1,600 calories per day - much less than the 2,000-2,500 calories most average Americans consume each day.

"I just knew that too much food makes you fat and if you don't burn off more energy than you consume you're going to get fat," says Zac.

Zac began his calorie-restricted diet in January to lose weight. At 5'9" and 187 pounds he was overweight and knew eating less and exercising more would help. He started by reducing his liquid calories; cutting out soda and skipping the two beers he used to drink every day. Now he drinks water and tea. Meals consist of lean proteins like chicken breast and fish and high-fiber foods like beans, broccoli and greens. Portions are small, but eating more meals throughout the day keeps Zac from getting hungry.

"I try to eat what's going to fill me up the most. That's where the high-fiber foods come in," adds Zac. "And I keep it simple by eating the same thing for breakfast and lunch every day so the only meal I have to plan for is dinner."

Workouts five days a week - a mix of running and climbing the rock wall at a gym near his home - round out Zac's weight loss plan. And so far, the plan is working. He's lost 26 pounds since January - an average of 2 pounds per week.

Calorie restricted diets have become extremely popular in recent years. A simple Google search turns up more than 2 million websites related to calorie restriction. Many people are turning to what they call "the CR lifestyle" not just to lose weight, but because they believe it will help them slow the aging process and live longer. Studies testing calorie restriction on insects, worms, mice, and rats found that animals on restricted diets lived longer than their normal-diet counterparts and were less likely to develop the chronic diseases that become more common as we age, such as diabetes and heart disease.

But it's still not clear that humans can benefit from calorie restriction the same way some animals do. All the testing done so far has focused solely on animals with life spans much shorter than humans.

"What we know is that it can be safely done," says Dr. George Blackburn, Director of the Center for the Study of Nutrition and Medicine at Beth Israel Deaconess Medical Center. "But who and how it benefits longevity is still the focus of current research."

There are health benefits and dangers to calorie restriction. Losing weight can lower your risk for cancer, Type 2 diabetes, and heart disease. But if you lose too much weight too quickly, you could be doing your body more damage than good.

"If someone loses more than 1-2 pounds a week, they are probably losing muscle mass as well as water weight," says Carine Corsario, Exercise Physiologist at the Tanger Be Well Center at BIDMC. "The problem with losing this muscle mass is that it will actually slow down your metabolism so you are expending fewer calories when at rest."

Corsario also warns that when you're eating less, you may be robbing your body of the vitamins and minerals it needs to stay healthy. Both Corsario and Dr. Blackburn recommend medical supervision if you are attempting a calorie restricted diet.

"Talk to your physician before you start. Find out if you have any medical conditions that should be monitored while you follow the calorie-restricted diet. Ask if you need any lab tests and when you should return for a follow-up visit," advises Dr. Blackburn.

Zac doesn't plan on staying on his calorie-restricted diet much longer. He hopes to reach his target weight of 158 pounds in the next few weeks and then bring back some of the foods he's missed during his diet - like desserts and beer - but in moderation.

"It really hasn't been hard. I rarely cheat," says Zac. "Some days I feel better than others, but that's how I felt before the diet."

Above content provided by Beth Israel Deaconess Medical Center. For advice about your medical care, consult your doctor.