New insights into calorie restricted diets

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Day-on, day-off diet boosts health

 

22:00 28 April 03

 

NewScientist.com news service

 

Eating double portions one day and nothing the next delivers the same health

benefits to mice as seen in animals whose lifespan has been extended by

restricting their calorie intake.

No one is suggesting people adopt such a diet. But the study adds to the

evidence that caloric restriction works by activating some kind of protective

mechanism, rather than simply being a result of eating less and thus suffering

less damage as food is metabolised. If this is the case, there may be ways to

switch on the protective mechanism without going on a crazy diet.

Both calorie restriction and intermittent fasting prompt cells in the body

to set up defences against stress that also protect against ageing and

degenerative diseases, concludes team member Mark Mattson, at the US National

Institute on Aging's Gerontology Research Center in Baltimore.

These might be adaptations that benefited people in the past. " A

three-meals-a-day diet only occurred recently in human evolution, " he says.

" Often we

were probably forced to go days without food. "

But whether such a radical diet would benefit people now is not clear. Mice

that start a restricted diet late in life do not always live longer.

Furthermore, while occasional one-day fasts are thought to be harmless, they are

not

necessarily pleasant. " People feel tired, irritable and lethargic, " says Alex

Johnstone of the Rowett Research Institute in Scotland.

 

Long life

 

From worms to mice, virtually every kind of animal fed a reduced calorie diet

has been found to live longer - up to 40 per cent longer in some cases. But

it has yet to be shown that such a diet extends human life.

Previous studies suggested intermittent fasting might also extend lifespan.

But as most rats and mice lose weight on such a diet, it was not clear if this

was really any different from caloric restriction. So Mattson and his

colleagues tried it on a strain of mice that does not lose weight on a day-on,

day-off diet.

From the age of nine weeks, they let one group of mice eat freely, fed

another group 40 per cent less than the eat-all-you-like group and gave a third

group all they wanted one day and nothing the next.

The mice on the reduced calorie diet weighed only about half as much as

those allowed to eat all they wanted. But the intermittently fed mice did not

lose

any weight, since they ate almost twice as much on days when they were

allowed food.

 

Low insulin

 

Crucially, these mice displayed most of the same physiological changes as

mice on restricted diets. Levels of glucose and insulin in the blood of fasting

mice were even lower than those on a restricted diet, both factors that may

contribute to increased longevity.  

Caloric restriction has also been shown to protect against neurodegenerative

diseases and the brain cells of the fasting mice were better at withstanding

exposure to a neurotoxin than those of mice on a restricted diet.

However, Johnstone warns against people adopting something as radical as the

day-on, day-off diet without medical supervision: the dangers include sudden

death due to heart failure. Fasting for a longer period, such as a week, is

also dangerous, her work shows.

Both Johnstone and Mattson are now planning studies looking at the effects

of intermittent fasting in people.

Journal reference: (Proceedings of the National Academy of Sciences:

DOI:10.1073/pnas.1035720100)

 

 

Kurt Kleiner