The Quest to Learn Why Slashing Calories Extends Life

Scientists have known for a long time that rats, mice, and worms that eat very little live longer than those that eat normal diets. Now, the results of research on humans are starting to emerge. It may take decades to prove that people who carefully regulate their calories and eating patterns extend their life span, but at the very least, some scientists say, these people may avoid many health problems associated with aging.

This spring scientists issued a report documenting the health benefits on a small group of people between ages 35 and 82 who decided to severely restrict their calorie intake simply on the basis of what is known about laboratory animals. These people have a lower risk of heart disease, as well as reduced chances of having a stroke or getting diabetes. Incidence of these three conditions generally increases markedly as people age.

Over a three-year period, Holloszy’s team at Washington University compared 18 people who had, in hopes of slowing the aging process, independently eaten a calorie-restricted diet for at least six years, and 18 healthy, non-obese study participants who ate typical Western diets. Their findings appeared the Proceedings of the National Academies of Sciences.

The study volunteers consumed from 2,000 to 3,550 calories per day, and the calorie restriction group consumed between approximately 1,000 and 2,000 calories per day.

The dietitian-approved meal plan is carefully balanced: The calorie restriction group consumed about 26 percent of their calories from protein, 28 percent from fat, and 46 percent from complex carbohydrates. The fare was enlivened by a nutrient-dense array of fruits, vegetables, legumes, and whole grains.

“Calorie restriction is not about starvation,” says Chhanda Dutta, chief of the Clinical Gerontology Branch of the National Institute on Aging in Bethesda, Maryland. “It’s about lowering caloric intake, minus malnutrition.”

The calorie-restriction subjects scored vastly better on all major risk factors for heart disease including total cholesterol, triglycerides, and blood pressure. Each of these tends to increase with advancing age. They also have very low amounts of body fat compared to the average person in the control group, who had about 25 percent body fat.

This quality protects the calorie restrictors from the type 2 diabetes associated with obesity, Holloszy says.

In addition, three people in the calorie restriction group had familial high cholesterol when the study began. According to Holloszy, calorie restriction reduced their cholesterol levels, and they no longer take cholesterol-lowering medication.

“The amazing thing is that regardless of their genetic background, they all showed the same response,” he says.

And their blood contained negligible amounts of the protein (CRP) known to cause inflammation, which is increasingly believed to be a factor in diseases

Of the 18 participants, many had practiced the calorie restriction diet for years, and kept scrupulous records of their health and food intake.

“We’re a ready population they could use to do a quick comparison against a standard population,” says Pomerleau. “It’s hard to get people to volunteer to eat like this.”

Since he began “serious” calorie restriction in 2000 at age 35, Pomerleau’s weight has dropped from about 170 to his current lean weight of 123. He calculates that, based on data from the animal studies, every calorie you avoid is worth about 30 seconds of extra life.
Or, Pomerleau says, putting it another way, “I’m more than willing to give up a piece of pizza to live another three hours.”

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