Calorie restriction helps regulate glucose and maintain gray matter volume in the brain.

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 current study utilized 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 imagining (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."