Eat less, have more immune cells

WHEN it comes to food, moderation may be the best strategy. Calorie-restricted diets have long been thought to extend lifespan, but no one could find a reason why. Now Janko Nikolich-Zugich of Oregon Health and Science University in Portland and his colleagues have discovered that the immune systems of older primates on a restricted diet are "younger" and function better than those of their peers on a normal diet.

Previous studies on the effects of caloric restriction in humans and other primates have yielded mixed results, although there is some indication that it could help prevent heart disease, diabetes, stroke and even cancer.

For up to 18 years, Nikolich-Zugich and his team kept a group of rhesus monkeys on a diet of around 30 per cent less calories but the same nutritional value as the normal diet of captive monkeys. Usually, as the immune system ages, the number of naive T-cells - white blood cells that detect and fight new pathogens as they enter the body - diminishes, making the body more susceptible to disease. However, monkeys on the reduced-calorie diet maintained higher levels of naive T-cells for longer than the control group (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0606661103).

Nikolich-Zugich believes the findings could have dramatic implications for humans. "If we could restore weakened immune systems we could protect many more people," he says.

Luigi Fontana of Washington University in St. Louis, Missouri, who studies nutrition and ageing in humans, says the findings are surprising, since no strong link between caloric restriction and the immune system has been found before in humans and primates. "This adds another important piece to the puzzle," he says. "It suggests that not only are cardiovascular and metabolic systems younger in calorie-restricted animals, but that caloric restriction also slows down the ageing of the immune system."

However, Richard Weindruch at the University of Wisconsin in Madison cautions that the study did not prove that the monkeys actually lived longer.

Nikolich-Zugich plans to continue his studies to better understand how caloric restriction works at the molecular level, but says he would not advocate following a calorie-restricted diet for the time being, since the benefits must be weighed against the adverse effects of lower nutrition. Studies in rodents suggest that caloric restriction is not beneficial if it is started too early or too late in life, he says.