If you’re in your 30s or 40s and blame your metabolism for your declining fitness, we have some surprising news: it probably hasn’t changed much since your 20s.
Contrary to popular belief, the rate at which humans burn calories remains relatively stable through your 20s to your 50s, according to new research. It is not until age 60 and beyond that metabolic rates really start to decline.
Researchers analysed calories expended by more than 6,600 people aged between one week and 95 years old across 29 countries as they went about their daily lives.
Results show that babies do experience a surge of metabolic rate, with a one-year-old using up calories 50% faster for their body size than adults. However, this surge reduces very gradually through childhood and stabilises in much of adulthood.
The study sheds new light on the widely held belief that teenage years and a person’s 20s are when calorie-burning hits its peak, the researchers said. Instead, it peaks at one, tanks at 60, and stays relatively stable in between.
The study, published in the journal Science, was the result of work by an international team of scientists including Professor John Speakman, from the University of Aberdeen.
Professor Speakman, a senior author on the paper, said: “An infant’s ‘gas-guzzling’ metabolism may partly explain why children who don’t get enough to eat during this developmental window are less likely to survive and grow up to be healthy adults. After this initial surge in infancy, the data show that metabolism slows by about 3% each year until we reach our 20s, when it levels off into a new normal.”
Despite growth spurts during teenage years, researchers said there was no uptick in daily calorie needs in adolescence after controlling for body size.
They concluded that energy expenditure during the 20s, 30s, 40s and 50s is the most stable, with metabolism not declining again until after age 60. The slowdown is gradual at just 0.7% a year, but someone in their 90s needs 26% fewer calories per day than someone in midlife.
If your body feels more sluggish in your 30s or 40s compared to your 20s, we hate to break it to you, but your lifestyle may be the culprit.
Professor Herman Pontzer, of Duke University in North Carolina in the US, said: “We really thought puberty would be different and it’s not.
“Midlife was another surprise. Perhaps you’ve been told that it’s all ‘downhill after 30’ when it comes to your weight, but while several factors could explain the thickening waistlines that often emerge during our prime working years, the findings suggest that a changing metabolism isn’t one of them.”