A new study suggests that exercising in early life can have health benefits that last well into middle age.
According to the World Health Organization (WHO), childhood obesity is "an urgent and serious challenge" in many countries across the globe. Whereas in 1990 there were approximately 32 million obese children between 0 and 5 years old, this number jumped to 42 million by 2013.
Not only are children with obesity at a higher risk of developing numerous diseases, but the effects of obesity in childhood are far-reaching, and such a weight problem is very likely to persist into adulthood.
But could these effects be staved off with physical activity early in life? More specifically, could physical activity in childhood have long-lasting effects on metabolism and bone health later in adulthood?
A new study - published in the journal Frontiers in Physiology - suggests that exercising early in life can change how the body metabolizes calories and how it responds to a high fat intake much later in life.
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.
Link between exercise, fat, and bone health
The decision to investigate whether or not early life exercise can change the effects of a high-fat diet in later life was spurred by previous studies that examined how "mechanical loading" affects bone marrow gene expression.
Mechanical loading refers to the mechanical stimulation induced by physical activity. The process has consequences on a cellular level, impacting bone formation and bone loss.
Therefore, not only is physical activity positive because it helps the body to burn fat, but it can also reduce bone mass loss and improve bone health.
As Prof. Firth explains, "Bone metabolism strongly influences energy metabolism in the body, and metabolism - what you do with energy from diet - is the central crux of why some children and adults become obese."
Some studies referenced by the authors have shown that a high-fat diet reduces the ability of bone marrow stromal stem cells to differentiate into cells that form new bone, or osteoblasts, in female mice.
Other studies have shown that mechanical stimuli, such as those induced by physical activity, promote osteogenesis - but none of those looked at the combined effects of high-fat diet and exercise.
Furthermore, physical activity is known to reduce inflammation, which is caused by excess fat. Prolonged inflammation induced by high-fat diets can damage the cells and tissue in the body, leading to heart disease, diabetes, cancer, and other conditions in the long run. However, exercise helps to annul some of these negative effects by turning down the genes responsible for low-grade inflammation.
For all the reasons mentioned above, Dr. O'Sullivan and colleagues set out to examine the relationship between early life exercise, bone health, and metabolism in male rats on high-fat diets.
Early life exercise impacts mid-life health
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.
Additionally, 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."
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."