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Immune Systems Stronger In Rats Fed Low-Calorie Diets

March 29, 1988

SOUTH BEND, Ind. (AP) _ Scientists from a range of disciplines took up the question Monday of why rats fed a low-calorie diet lived longer, with two researchers suggesting lower food intake kept the animals’ immune systems strong.

The scientists, from the United States and Canada, gathered at the University of Notre Dame to analyze a study in which about 200 rats fed 30 percent fewer calories than a similar-sized group lived an average of 20 percent longer.

Immunology rresearchers Dr. Yoon Kim of Chicago and Dr. Kara Eberly speculated that the restricted diet may have exposed the rats to fewer antigens - or disease-causing agents in the food - to which the immune system reacts by producing antibodies.

With the immune system having fewer disease-fighting duties, it holds up longer, prolonging the rats’ lives, he said.

″In a restricted diet, the tendency is not to use up″ the immune system’s ability to fight disease, said Kim. ″Life, and healthy life, is due to restriction of diet, maintaining the potential of the defense system, not using it unnecessarily.″

The conference, taking place through Tuesday, will include papers by specialists in such fields as biochemistry, dentistry, nutrition, physiology, pathology and gerontology.

Thrity-two researchers were sent tissue samples for analysis from the 400 rats raised at Notre Dame’s Lobund Laboratory in a study on the effects of diet on aging.

The study was supported by by the Chicago-based, non-profit Retirement Research Foundation.

Dr. Gilbert Boissonmeault, a clinical nutritionist from the University of Kentucky, said he found no difference in the body fat content between the two groups of rats.

A study by Dr. Gibbons Cornwell III, a professor of medicine at Dartmouth College, found no significant differences in heart disease.

Additional studies on why the rats on a low-calorie diet lived longer will look at the glandular system and gastrointestinal tract.

The study involved 400 rats, half of which were fed 12 grams of food per day, or about 70 percent of normal, with fat limited to 5 percent.

Animals on restricted diet lived an average of 38 months, an increase of nearly 20 percent above the control group, scientists said.

The rats on restricted diets were healthier in their old age and developed fewer cancers of the prostate and liver. The rats also suffered less disease of the heart and brain and had better-functioning immune systems, scientists said.

″I think the studies support the wisdom of what is commonly referred to as a prudent diet,″ said Dr. Richard Weindruch of the National Institute on Aging. ″Don’t overload yourself with calories.″

But he added: ″The studies at present do not justify a recommendation to the general public of severe caloric restriction, or even moderate caloric restriction, because there are so many difficulties in translation between the animal model and the human situation.″

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