Diet diehards eat less to live longer

Inspired by animal experiments showing that underfeeding enhances vitality and prolongs life by 30 percent or more, the US-based Calorie Restriction Society is slashing calorie intake in a bid to beat back the clock and halt the ageing process.

Some people are doing it strictly to enhance longevity, while others do so to avoid age-related disease, or because they already have diabetes, high cholesterol or clogged arteries and want to clean up their bodies by using diet.

"Even if they were to reduce their calorie intake by half, they would still only be at baseline," the optimal balance between energy input and output according to the study.

A wealth of scientific evidence has confirmed that maintaining that balance helps prevent type-2 diabetes, cardiovascular disease and cancer.

But experiments with both animals and humans have also shown that pushing one's calorie intake 10 to 20 percent below that baseline threshold -- without lowering nutrients -- may provide additional health advantages.

Luigi Fontana, a professor in the Division of Geriatrics and Nutritional Science of Washington University in St. Louis, Missouri, has led or co-authored more than a dozen studies on reduced calorie intake in humans.

He is also one of a handful of researchers studying longterm impacts by monitoring a group of nearly 50 adults who have been on calorie restriction diets for at least a decade.

"Most are middle-aged, but they have the cardiovascular profile of a teenager," he said by phone.

Blood pressure, cholesterol, blood sugar and insulin levels are all low while so-called "good" cholesterol remains high, he said. Diabetes and cancer rates are down too.

Studies published earlier this year point to other, specifically age-related, benefits as well.

One shows that cutting calorie intake 20 percent cut damage in DNA and RNA caused by oxidation in half compared to control groups.

Oxidative damage to DNA, proteins and other cellular building blocks accumulate over time and are thought to be a major driver of ageing.

A second study by Fontana, published in July in Aeging Cell, shows that a combination of calorie reduction and limiting protein intake lowers levels of insulin-like growth factor, commonly known as IFG-1.

IFG-1 is a high-risk marker for prostate, breast and colon cancer, and plays a key role in regulating cell growth linked to the ageing process.

Consuming less calories does not necessarily mean eating less food, he said. While he only takes in two meals a day, he tucks away large quantities of fruits and vegetables, along with smaller portions of lean meats and fish.

Refined, processed foods high in sugar, fat or salt -- junk food, in other words -- is off the menu.

The average calorie intake for men is about 1,800, and for women between 1,200 and 1,600, depending on height.

Tests with monkeys underway for two decades give no indication that life in primates can be extended by the 30 or 40 percent seen in rats and mice.

"Will this add 10 years to your life? Nobody knows," said Leeuwenburgh, adding that reducing calories late in life could make it difficult to maintain needed muscle mass.

"But one thing is sure -- calorie restriction will help you reach your maximum lifespan potential, which is different for all of us depending on our genetic profile," he said.