Calorie restriction practitioners stay young at heart
Tuesday, June 12, 2012. An article published online on May 21, 2012 in the journal Aging Cell reports the outcome of a study of humans who voluntarily practice calorie restriction which suggests that the practice helps preserve heart function, in addition to many other benefits.
"Caloric restriction retards aging in laboratory rodents," write Luigi Fontana, MD, PhD and his colleagues at Washington University School of Medicine in St Louis in their introduction to the article. "No information is available on the effects of long-term calorie restriction on physiologic markers of aging and longevity in humans."
The study evaluated heart rate variability as a marker for cardiac autonomic functioning in 22 subjects whose calorie intake was approximately 30 percent lower than normal, and 20 men and women of the same age (which ranged from 35 to 82 years) who consumed a standard Western diet. Heart rate variability as measured by 24-hour heart monitoring in the calorie restricted group was found to be comparable with normal values for healthy individuals 20 years younger. The difference between the calorie restricted and normal group was similar to that induced by the drug atenolol, which is used in cardiovascular disease and hypertension. "This is really striking because in studying changes in heart rate variability, we are looking at a measurement that tells us a lot about the way the autonomic nervous system affects the heart," Dr Fontana stated. "And that system is involved not only in heart function, but in digestion, breathing rate and many other involuntary actions. We would hypothesize that better heart rate variability may be a sign that all these other functions are working better, too."
"Higher heart rate variability means the heart can adjust to changing needs more readily," explained lead author Phyllis K. Stein, PhD. "Heart rate variability declines with age as our cardiovascular systems become less flexible, and poor heart rate variability is associated with a higher risk of cardiovascular death."
"In many of our studies, we have found that a number of metabolic and physiologic changes that occur in calorie-restricted animals also occur in people who practice calorie restriction," Dr Fontana noted. "The idea was to learn, first of all, whether humans on calorie restriction, like the calorie-restricted animals that have been studied, have a similar adaptation in heart rate variability. The answer is yes. We also looked at normal levels of heart rate variability among people at different ages, and we found that those who practice calorie restriction have hearts that look and function like they are years younger."
"But we can't be absolutely positive that the practice of calorie restriction is solely responsible for the flexibility of the cardiovascular system," Dr Stein added. "People who practice calorie restriction tend to be very healthy in other areas of life, too, so I'm pretty sure they don't say to themselves, 'Okay, I'll restrict my calorie intake to lengthen my life, but I'm still going to smoke two packs a day.' These people are very motivated, and they tend to engage in a large number of very healthy behaviors."
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In an article published online on March 13, 2012 in the journal Diabetes, Sterling C. Johnson and his colleagues at William S. Middleton Memorial Veterans Hospital and the University of Wisconsin report a benefit for calorie restriction in glucose regulation and related improvement in brain volume in older rhesus monkeys.
The research included 27 monkeys that received calorie restricted diets beginning in middle age and 17 control monkeys that were allowed to eat as much as they wanted for eight hours per day. To investigate the hypothesis that calorie restriction, via its positive effect on insulin signaling, could improve neural atrophy related to insulin dysregulation in areas of the brain affected by neurovascular and neurodegenerative disorders, the researchers evaluated insulin resistance through the use of glucose tolerance testing and insulin measurement, and assessed regional brain volumes using magnetic resonance imaging (MRI). Motor task learning and performance were analyzed in 26 animals.
While six of the control animals had preclinical or diabetes-like glucoregulatory dysfunction, no calorie restricted animals were found to have glucoregulatory impairment. Increased insulin sensitivity predicted increased gray matter in the parietal and frontal cortices of both groups; however, each unit increase in insulin sensitivity predicted more gray matter in the hippocampus, prefrontal cortex and other regions with a high density of insulin receptors in the calorie restricted group relative to the control animals. Hippocampal gray matter volume adjusted by insulin sensitivity was correlated with learning and memory and performance.
"In summary, increased insulin sensitivity among calorie restricted monkeys was associated with more gray matter in parietofrontal cortices, hippocampus, and other regions that vary in insulin receptor density and signaling," the authors conclude. "Among controls, higher insulin sensitivity showed a positive relationship with gray matter volume in parietofrontal cortices with low insulin receptor density, but predicted less gray matter in structures and areas that have high receptor density. Calorie restriction or calorie restriction mimetics may benefit some specific brain regions and aspects of task learning and performance."
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