By Elisa Zied, R.D.
msnbc.com contributor
updated 10/5/2007 8:55:47 AM ET 2007-10-05T12:55:47

Would you commit to eating a lot less if it helped add a few years to your life?

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A small, but growing group of extreme dieters believe that by drastically limiting the amount of food they consume, they'll not only slow the aging process, but avoid heart problems, diabetes and other chronic diseases.

Calorie restriction, also known as CR, may never be the next Atkins or South Beach Diet, but the movement is getting more attention from longevity-obsessed Baby Boomers. It has spawned a flurry of books, including "The Longevity Diet," "The Anti-Aging Plan," and "Beyond The 120 Year Diet."

Unlike typical diets that focus primarily on weight loss, CR is about reducing long-term calorie intake and consuming adequate nutrients at the same time in the pursuit of a more energetic old age. Numerous studies have shown that eating less can help rodents and primates live longer and healthier. People who follow CR claim that cutting calories, which leads to weight loss and a slower metabolic rate, can lengthen the human life span as well.

While there is no specific meal plan, followers generallyeat 20 percent to 30 percent less than whatis normally recommended. Sugar, saturated fats, and most dairy are no-no's in calorie restriction, with bulky foods like vegetables, fruits, and grains providing most of the calories.

Fighting heart disease
Some people may wonder if giving up chocolate or ice cream for life is really worth it.

No long-term human studies have tested CR’s impact on longevity, but there is considerable evidence it reduces several risk factors for cardiovascular disease and diabetes.

A one-year study published in the July 2007 issue of the AmericanJournal of Physiology, Endocrinology and Metabolism compared the effects of an extremely low-calorie diet and exercise on coronary heart disease risk factors in lean and overweight middle-aged adults.

Both calorie restriction (consuming 20 percent fewer calories) and exercise (expending 20 percent more calories) lowered bad (LDL) cholesterol, raised good (HDL) cholesterol levels, and improved insulin resistance, but only calorie restriction led to significant declines in risks associated with heart disease and heart attacks.

A study published in Proceedings of the National Academy of Sciences of the United States of America in 2004 found that people who restricted calories by 30 percent for an average of six and one-half years had lower total and LDL cholesterol, higher HDL cholesterol, and lower triglycerides than those who followed a typical American diet.

There’s also some evidence that the diet can improve blood glucose control, which can help prevent diabetes.

Serious risks
But the calorie-cutting quest for the fountain of youth can also lead to some real health problems. Some people admit to feeling constantly hungry and become obsessed with food. Some doctors believe that calorie restriction can attract people who are susceptible to eating disorders, such as anorexia nervosa.

People who try restricting calories can experience rapid weight loss, although it seems to plateau after six months as their bodies adjust, according to studies. For people who have little body fat even modest calorie restriction can be harmful, the researchers argue.

Dieters who restricted calories for 12 months had lower muscle mass and a reduced capacity to perform exercise compared with those who lost similar amounts of weight from exercise alone, according to a study published in the Journal of Applied Physiology in February 2007. CR-induced weight loss (but not exercise-induced weight loss) was associated with reduced bone mineral density at the hip and spine (high risk areas for fracture), another study published in Archives of Internal Medicine in March 2007 found.

Other possible risks or side effects associated with the spartan diet include increased cold sensitivity, menstrual irregularities, and infertility.

Researchers at the Washington University School of Medicine in St. Louis found that excessive calorie restriction causes malnutrition and can lead to anemia, muscle wasting, weakness, dizziness, lethargy, fatigue, nausea, diarrhea, constipation, gallstones, irritability and depression. The study was published in the March 2007 issue of the Journal of American Medical Association.

While earlier studies have linked calorie restriction to memory and attention problems, a recent study published in the June 2007 issue of Rejuvenation Research found no significant connection between the diet and cognitive impairments.

Take it slowly
Cutting calories by more than 500 per day (recommended in most other diet plans) will likely be too difficult and unrealistic for most people to follow long-term.While there may be some disease-fighting benefits from eating a lot less for the rest of your life, it won't guarantee 100 candles on your (sugar-free) birthday cake.

If you're looking to lose weight, it's best to take it slowly. Most experts recommend 1 to 2 pounds a week as a safe, realistic weight-loss goal. A healthy body mass index (BMI) is 18.5 to 24.9 (at 5’4”, that’s a weight of 108 to 145 pounds).

Still, most of us could benefit from modest calorie cutbacks and incorporating mostly whole grains, fruits, vegetables, lean meats, beans, and low-fat dairy foods into our diets. Combining that kind of diet with exercise – a proven disease-fighter — can help you achieve a healthier body weight, preserve muscle and bone, and give you a psychological boost.

And you can still enjoy a little chocolate now and then.

Elisa Zied, RD, is a spokesperson for the American Dietetic Association. She is the co-author of “Feed Your Family Right!” and “So What Can I Eat?!”

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