Science has shown that diets that veer close to starvation can make everything from mice to monkeys live longer. But can such a strict eating regimen prolong human lives, and if so, would those extra years be healthy, happy ones?
Recent research from Washington University scientists found that people who slashed their kilojoule intake have lower core body temperatures than those who eat more. Core body temperature is the temperature at which all of the functions in the body can operate at maximum efficiency, so the link looks like a positive one, according to some researchers.
Trent Arsenault, a 35-year-old engineer in the Bay Area, certainly hopes so. He has been a "kilojoule restrictor" since 2000, consuming just 7,500kJ a day or 25% less than what a male of his size - 6-foot-1 and 70kg - would normally consume, he said.
Since he started, he has shed 27kg and now has a body-mass index of 19, just one notch above underweight (which is 18). His body fat composition is only 10%.
Study on kilojoule restricted diets
Arsenault is also one of 28 participants in the first long-term clinical trial to look at extreme kilojoule restriction in humans, and its effects not only on longevity but also on health.
He was recruited with the help of the Calorie Restriction Society, an international organisation with several thousand members.
The study is known as CRONA (Caloric Restriction with Optimal Nutrition and Aging Study). It is being done at the University of California, San Francisco, where participants from many different states as well as England and Japan are travelling for a weekend of tests including cognitive exams, body measurements and a visit to an egg-shaped chamber that measures body fat composition. They'll also complete surveys on everything from their medical history and eating habits to sleep patterns and stress levels.
"It's an interesting paradox because restriction in animals seems to be the fountain of youth, but all my prior work in humans has shown not such great outcomes," said Janet Tomiyama, a psychologist who is a Robert Wood Johnson Foundation Health & Society Scholar at UCSF and principal investigator of this trial.
And the animal studies haven't had clear data on how well the animals are actually living.
Personality in dieters
"The animal data seems good with all the longevity studies but what people really don't know is how healthy the animals actually are," said Heidi A. Tissenbaum, an associate professor in the Program in Gene Function and Expression and in molecular medicine at the University of Massachusetts Medical School in Worcester. "How happy are the people? Are they feeling restricted all their life?"
Not only will the investigators be looking at cholesterol and other markers of health, but they will also measure the length of telomeres. These are pieces of DNA which, when shortened, seem to be linked with health problems and a shorter life-span.
Among other things, the study will look at how personality might differ in kilojoule restrictors compared to normal eaters or overweight/obese people, as well as cognitive ability, impulse control and how stress is handled.
The study participants are mostly male (as are most kilojoule restrictors), well-educated and middle-aged. It will take decades to have results from the trial but Arsenault feels he already has seen a difference.
He doesn't catch colds or the flu, has plenty of energy and neither his sexual drive nor his fertility have been affected, he said. In fact, he has fathered at least 15 children through a sperm bank since he started restricting kilojoules.
Unlike many kilojoule restrictors, Arsenault did not have a mid-life health scare which propelled him into action. Instead, at the age of 25, he realised he wanted to concentrate on his career, postponing marriage and children.
"[I wanted to] keep myself looking decent enough so that in 10 years I could get married and still be healthy enough to spend time with kids," he explained.
The study is funded by the Appleby Foundation, the Robert Wood Johnson Foundation Health & Society Scholars program and the University of California, Berkeley Population Center. Researchers Elizabeth Blackburn, Elissa Epel and Jue Lin are also co-founders of a new company called Telome Health Inc., which is developing applications of telomere biology to improve health.
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