The jury is still out on whether caloric restriction can prolong human life or prevent age-related diseases, but the results of recent studies with rodents and rhesus monkeys are moving us closer to a verdict. Richard Weindruch, Ph.D., professor of medicine at University of Wisconsin-Madison and one of the nation’s top caloric restriction researchers, shares some thoughts about this promising area of research.
Is caloric restriction a new idea?
We have known for 60 years that caloric restriction, done without skimping on nutrients, works remarkably well in rodents. It greatly extends their maximum life span and decreases the incidence of cancer and other late-life diseases. In fact, of all the things that have been attempted in laboratory rodents, only caloric restriction has succeeded in increasing maximum life span.
What new information do we have?
More recent studies with both mice and rhesus monkeys confirm the earlier results and show the potential for even greater benefits. In addition to living longer, we (and other researchers) have found that rodents on calorie-restricted diets (ingesting half as many calories as the control group) stay “younger longer” — as judged by hundreds of age-sensitive biologic parameters, including immune system aging, eye lens proteins, enzyme activities, and learning and behavior. Even rodents who were started on a calorie-restricted diet in middle age or later showed positive results, such as a slowing of skeletal muscle loss.
What’s the status of your ongoing research with rhesus monkeys?
We’re coming into a very exciting time in our rhesus monkey studies, which have received additional funding from the National Institutes of Health. The first of our three groups of monkeys, which we began studying in 1989, will soon become old, and they’re showing changes in physiology. This will allow us to observe differences in how they age. It will also help us determine if caloric restriction retards aging and age-related diseases in non-human and human primates. Although this study is 15-20 years away from completion, we already have solid evidence that the calorie-restricted group of monkeys is more resistant to developing Type II diabetes and shows fewer signs of spinal osteoarthritis.
How does caloric restriction work?
One of the next steps is figuring out the exact mechanism at work. That’s what fascinates me, and we are testing a few hypotheses. Many scientists, including myself, believe there is a link between aging and the cumulative damage to the body caused by “free radicals” — tiny, electrically charged particles created during energy production in the cells.
A research team at Southern Methodist University found that the mitochondria in the brain, heart and kidney cells of calorie-restricted mice produce lower amounts of free radicals and show less damage compared to mice who were fed a regular diet. It could be that fewer calories mean lower consumption of oxygen by the mitochondria, or that low-calorie diets increase the mitochondria’s oxygen-burning efficiency. Once the process is better understood, drugs could be developed to reduce free radical production or limit the damage they cause. I also hope that, in the near future, better appetite suppressants will be developed to help people who want to restrict their caloric intake.
What does this mean for people?
The effect of caloric restriction on humans is not yet known. And even if the results do prove meaningful in human terms, it remains to be seen whether people will actually do anything about it. Human behavior is complex. Whether it involves diet, exercise, not smoking, or wearing seat belts, people often do not make the choices that help them live longer, healthier lives.