The new study was carried out by Ph.D. student Dharani Sontam, Prof. Mark Vickers, Prof. Elwyn Firth, and Dr. Justin O'Sullivan, all of whom are from the Liggins Institute University of Auckland in New Zealand.
The researchers divided 80 male rates that were 22 days old into two groups: one chow-fed group (in which the rats were fed a normal diet and were allowed to move spontaneously in their cages) and a high-fat group.
The high-fat rats were divided further into three subgroups: a high-fat sedentary group (which was not given access to a running wheel), a high-fat, late exercise group (which was given a wheel after day 67), and a high-fat, early exercise group (wherein the baby rats were given an exercise wheel from day 22).
The scientists then extracted and sequenced RNA samples, analyzing gene expression and the molecular pathways that show how gene expression affects biological functions.
Dr. O'Sullivan and colleagues found that in the high-fat, early exercise group, the genes that are associated with increased inflammation were turned down.
Also, exercise changed the way the rats' metabolism responded to the high-fat diet by changing the pathways responsible for transforming fat into energy.
These effects lasted for at least 60 days after the rats had stopped exercising. The results indicate that the bone marrow of the high-fat, early exercise rats retained a long-lasting memory of the physical activity.
"What was remarkable was that these changes lasted long after the rats stopped doing that extra exercise - into their mid-life. The bone marrow carried a 'memory' of the effects of exercise. This is the first demonstration of a long-lasting effect of exercise past puberty, "said Dr. Justin O'Sullivan.
"The rats still got fat," explains Dr. O'Sullivan, "but that early extra exercise basically set them up so that even though they put on weight they didn't have the same profile of negative effects that [are] common with a high-fat diet."
The findings may explain why some people are obese without having any of the negative health consequences commonly associated with obesity, he says, concluding that the study "strongly emphasizes the health benefits of exercise for children."