For the first time, scientists have demonstrated a direct link between diet and vulnerability to neuron-damaging toxins in primates. New research with rhesus monkeys suggests that a restricted calorie diet could significantly lower the risk of developing neurological disorders such as Parkinson's disease, a progressive and incurable disease that causes loss of muscle control.
For many illnesses, including Parkinson's, age is a major risk factor. Researchers have long known that primates and other creatures live longer, healthier lives--at least in the lab--if they consume fewer calories, but how such diets fend off disease is poorly understood.
To examine the question, neuroscientists Mark Mattson and Donald Ingram of the National Institute on Aging in Baltimore, and Don Gash of the University of Kentucky in Lexington selected 13 male rhesus monkeys and put seven on a reduced calorie diet. Over the next 6 months, the reduced calorie group lost an average of 12% body weight. The team then injected a neurotoxin into the right side of the brain in all 13 monkeys to produce parkinson-like symptoms. Muscle control problems were about half as severe in the monkeys on the restricted diet, as measured by how far and fast they moved. Further, these monkeys had higher levels of dopamine--a crucial neurotransmitter that is depleted in Parkinson's patients--in a brain region called the striatum, which is important for movement.
The monkeys on the restricted diet also had about three times the levels of a protein known to protect the growth and survival of neurons--glial cell-line derived neurotrophic factor (GDNF)--in another brain region involved in movement. While this suggests GDNF may play a protective role, the connection between calorie-restriction and increased GDNF remains unclear. In a paper published online this week in the Proceedings of the National Academy of Science, the team speculates that a calorie-controlled diet throughout adulthood may reduce the risk of Parkinson's disease in humans.
The results need to be interpreted with caution, says Ole Isacson, a neuroscientist specializing in Parkinson's disease at Massachusetts General Hospital in Belmont, MA. "While calorie restriction did clearly mitigate the severity of Parkinson's in these monkeys, it doesn't help those who already have the disease," he says.