While caloric restriction doesn't appear to work for every species or even every strain of mouse, it remains one of the best established and simplest ways to extend lifespan in the lab. New data from mice hints it may well protect stem cell function, but severely knocks down the immune system
The good and the bad
Caloric restriction can increase lifespan by up to 50% in a number of organisms, but the picture in primates and humans is a little more complicated. It's looking like there may be both benefits and drawbacks to such a restricted diet.
The latest study from the Leibniz Institute on Aging reveals that under a 30% calorie reduction program mice hematopoietic stem cells, which give rise to red and white blood cells, remained in a quiescent state in response to some stresses and retained better function for a while after the diet. This means they reduced their activity, protecting themselves from deterioration but also dampening down the growth of new cells.
Bad news for the immune system?
Unfortunately the researchers discovered that these mice had noticeably reduced immune systems - with lymphocyte production reduced by up to 75%. This made the mice much more vulnerable to infection.
"The study provides the first experimental evidence that long-term caloric restriction – as intervention to slow down aging – increases stem cell functionality, but results in immune defects in the context of prolonged bacterial infection, too. Thus, positive effects of a diet are not transferable to humans one to one"
This may mean that any caloric restriction program, especially in the elderly, should be undertaken with care as infection in old age is a major cause of mortality. This doesn't discount the value of caloric restriction altogether and in certain cases careful fasting has indeed shown regenerative potential, but it highlights the need for more study in humans.
"In sepsis patients, we see a higher survival rate for those with a higher body weight than for patients who are very lean"
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