With a lot of the country in lockdown, there is a good excuse for weight gain at the minute, but if you are one of those people who blame a slowing metabolism for your weight gain, you might need to think again.
I’ll admit that I fall into that category. I used to eat anything I wanted when I was younger and I was often told by family members I had ‘hollow legs’ such was my ability to eat without putting on any weight.
When I did start to put on weight as I got older, it was an easy out to blame a slowing metabolism, but a Duke University study suggests that is wrong and that your metabolism rate doesn’t decline until much later in life.
Your metabolism is the rate at which your body burns calories, and this study has found that it actually peaks much earlier than life than previously expected, but it doesn’t start to decline until around 60 years of age.
Study co-author Professor Herman Pontzer said the research, which analysed the average calories burned by more than 6600 people ranging from one week old to age 95 as they went about their daily lives in 29 countries, found metabolism rarely changed throughout the stages of life.
“There are lots of physiological changes that come with growing up and getting older,” Prof. Pontzer said. “Think puberty, menopause, other phases of life. What’s weird is that the timing of our ‘metabolic life stages’ doesn’t seem to match those typical milestones.”
Some of the surprising results of the study revealed that infants had the highest metabolic rates of all, when it was previously thought that people reached their metabolic peak in their teens or early 20s.
The research found that energy needs spike during the first 12 months of life, and that by their first birthday, a one-year-old burns calories 50 per cent faster for their body size than an adult.
“Of course, they’re growing, but even once you control for that, their energy expenditures are rocketing up higher than you’d expect for their body size and composition,” Prof. Pontzer said.
While metabolism peaks as an infant, the data then shows it slows by about 3 per cent each year until we hit our 20s when it levels off to a new normal.
Then came the biggest surprise – that metabolism didn’t change in midlife, when a lot of people start gaining weight at some stage over the age of 30.
The study found that energy expenditure during our 20s, 30s, 40s and 50s was at its most stable and that metabolism didn’t really start to decline until after age 60.
The slowdown is gradual, too. It declines by around 0.7 per year.
Lost muscle mass as we get older may be partly to blame, the researchers say, since muscle burns more calories than fat. But it’s not the whole picture.
“We controlled for muscle mass,” Prof. Pontzer said. “It’s because their cells are slowing down.”
Prof. Pontzer said that because ageing goes hand in hand with so many changes it had been difficult to separate what was behind shifts in energy expenditure, but that the research suggested it was more than age-related changes in lifestyle or body composition.
“All of this points to the conclusion that tissue metabolism, the work that the cells are doing, is changing over the course of the lifespan in ways we haven’t fully appreciated before,” Prof. Pontzer said.
If it isn’t a slowing metabolism responsible for weight gain, then what is it? My GP is a big believer in the fact that people use less energy as they age, but don’t adjust their diet accordingly.
It is a simple explanation, but it is one that is supported by Swedish research that YourLifeChoices has previously reported on.
Have you gained weight as you have aged? At what age do you think you gained the most weight? What do you believe is responsible for your weight gain? Why not share your thoughts in the comments section below?
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