Skipping the donuts may preserve your brainpower. A new study finds that cutting calories by about a third protects nerve cells from damage caused by interrupted blood flow.
Blocking blood flow to the eye, in rats, mimicked the shortage of blood in the brain that causes the most common type of stroke.
"Whether an observation in rats will apply to humans is not known. But when we combine our findings with those from other studies, we see a pattern. It suggests that eating fewer calories may lead to a longer and healthier life," said Arthur H. Neufeld, Ph.D., the Bernard Becker Research Professor of Ophthalmology and Visual Sciences at Washington University School of Medicine in St. Louis.
Neufeld’s team reported its finding in the latest edition of the Federation of American Societies for Experimental Biology (FASEB) online journal FJ Express (http://www.fasebj.org).
The researchers studied rats with various risk factors for ischemic damage of the retina. They compared young rats to older rats, rats with diabetes to those with normal blood sugar, and rats on normal diets to those that ate 30 to 40 percent less food.
They tallied the loss of retinal ganglion cells — nerve cells crucial to vision — one week after briefly interrupting blood flow to the retina. As expected, the older rats had more damage than the younger ones: they lost about 40 percent of their retinal ganglion cells compared with 20 percent. Diabetic rats also fared worse than their nondiabetic counterparts.
Neufeld and colleagues placed both young and older animals on the calorie-restricted diet. The animals in these groups fed only three days a week for three months. The other groups had free access to food and water.
The young calorie-restricted animals gained 25 percent less weight as they matured than the other young animals. The older animals lost weight. They weighed about 16 percent less than the older animals that ate as much as they wanted.
Counting retinal ganglion cells after the interruption of blood flow, the researchers made a striking observation. "In both older and younger animals, caloric restriction protected retinal neurons from damage," Neufeld said. "After ischemia, younger animals lost almost 25 percent of their retinal ganglion cells, but in those on the calorie-restricted diet, the cell loss was closer to 15 percent. In older rats, retinal cell loss was about 30 percent in those eating a standard diet but only 20 percent in animals whose caloric intake was restricted."
Other researchers have found that animals on very low-calorie diets tend to live longer and are more resistant both to natural diseases and stress-related disorders. Preliminary research has suggested that restricting calories can protect certain brain structures from damage, but Neufeld and colleagues are the first to test the effects of a low-calorie diet on nerve cells in the eye.
There are two advantages to studying retinal neurons. "First, there are only about 100 thousand of them in the rat eye, so we can label every single one and determine exactly how many are lost," Neufeld said. "Second, we can injure these neurons without breaching the barrier between the bloodstream and the brain. That way, we know the damage isn’t caused by changes in the blood-brain barrier that might not relate directly to the initial ischemic injury."
Neufeld suggests these findings might apply to the loss of retinal ganglion cells in glaucoma as well as other neurons in the central nervous system. Retinal ganglion cells develop in the retina and then connect through the optic nerve, which goes into the brain. "So they are part of the central nervous system," he said.
He adds that the risk factors his team studied — aging, diabetes, diet — are known to influence the risk for stroke and other brain conditions. But in the study, aging had less of an effect when animals ate a low-calorie diet.
The retinal model should be useful for exploring the effects on nerve cells of other risk factors for stroke, such as hypertension, smoking and obesity. Neufeld also will use it to see whether drugs can protect neurons from ischemic damage.
Currently, the team is determining how neurons die after ischemia. "Are they killed by the initial injury, or do they commit suicide during the days or weeks after blood flow has been restored?" Neufeld asked. "We don’t know yet, but we hope to find out."
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This research was supported by grants from the National Eye Institute at the National Institutes of Health.
Kawai S, Vora S, Das S, Gachie E, Becker B, and Neufeld AH, Modeling of risk factors for the degeneration of retinal ganglion cells following ischemia/reperfusion in rats: effects of age, caloric restriction, diabetes, pigmentation, and glaucoma
FASEB J. published Mar 28, 2001, 10.1096/fj.00-0666fje. http://www.fasebj.org/express/
By Jim Dryden
drydenj@msnotes.wustl.edu