Around one-third of all teenagers in the UK are clinically overweight or obese, and it's rapidly becoming one of the greatest health challenges of our time. Now researchers may have identified one of the driving forces behind this epidemic, as they have discovered something surprising: The number of calories burnt by adolescents as they hit puberty dramatically drops, going against what we thought we knew about teenage development.
The majority of the calories we burn are spent maintaining our bodies, from keeping organs functioning to warming our blood, something that is known as our resting rate. It now seems that after the age of around 10 years old, the number of calories being consumed by teenagers' bodies sharply drops by around a full 25 percent. In real terms, this equates to roughly 500 calories, a not insignificant amount.
The findings by the research group are somewhat unexpected. With the massive growth spurts experienced by most adolescents in their teenage years, most presumed that the number of calories burnt would rise to account for this, but that is clearly not what is going on. After the drop at around 10 years old, the number of resting calories burnt doesn’t then increase until the teenager hits around 16 years of age. While the reasons behind this sudden drop in the burning of calories during puberty are still unknown, it may have deep evolutionary roots.
“We can only speculate as to why, but it could be a result of an evolutionary trait to save calories for growth that may now contribute to a dangerous rise in adolescent obesity in cultures where food is in abundance,” explains Professor Terence Wilkin, who co-authored the paper published in The International Journal of Obesity. “It could be that we have evolved to preserve calories to ensure we have enough to support changes in the body during puberty, but now we know they have sufficient calories each day, the drop in spend means excess weight gain.”
But that wasn’t all. The surprising drop in calories seen in the teenagers was also coupled with a drop in the amount of exercise that the adolescents undertook, a shift that was particularly pronounced in teenage girls. Both of these changes, the authors argue, are sufficient to explain why there is a sudden increase in the rate of adolescent obesity when young people hit puberty, something that had been observed before but never fully explained.
These results could have a significant impact on the health and advice given to young teenagers just hitting puberty, in an effort to try and cut the soaring obesity rates seen in many parts of the world.