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23.09.2008

Slim-waisted rats live longer

If you subject animals and people to chronic starvation they live twenty to thirty percent longer. Caloric restriction is the name given to a starvation diet intended to extend the lifespan. Researchers at the Albert Einstein College of Medicine in New York have discovered that part of the life-lengthening effect of caloric restriction is caused by the reduction in the amount of visceral fat that occurs as a result of following a strict low-calorie diet.

The New Yorkers did an experiment with rats. They gave the animals in the control group as much to eat as they wanted – in scientific language the rats were fed ad libitum (AL-fed). A second group of rats only got sixty percent of the amount of food that the AL-fed group ate – the caloric restriction group (CR).

There was a third group of rats as well. They were allowed to eat as much they wanted, but the researchers had surgically removed the visceral fat of these rats when they were five months old. This was the VF-removed group.

Visceral fat is the fat in the abdominal cavity that surrounds the organs. Health experts regard this as the most dangerous type of fat. Visceral fat can do more damage to the liver, the pancreas and the blood vessels around the heart than the fat on the legs, hips, shoulders and arms.

As the rats got older, the animals in the AL-fed group and the VF-removed group developed an equal fat mass and body weight. See below. The black bullets represent the AL-fed group and the squares the VF-removed group. The white diamonds [the lowest line in the graph] represent the CR-group.

The amount of fat in the AL-fed group and the VF-removed group was the same, even though the VF-removed group had hardly any visceral fat left.

The VF-removed group lived longer than the AL-fed group. They didn't live as long as the rats that underwent calorie restriction, but they did live longer, as the graph below shows.

The life-lengthening effect of removing the visceral fat is about one-fifth of that of caloric restriction. The rats in the CR-group also had hardly any visceral fat of course. The researchers therefore concluded that it was the absence of visceral fat that resulted in a fifth of the life-lengthening effect of caloric restriction.

The researchers suspect that visceral fat excretes harmful inflammatory proteins that interfere with the working of insulin and cause disease.

Sources:
Aging Cell. 2008 Jun;7(3):438-40.