Pontzer H et al. Daily energy expenditure through the human life course. Science. 2021 Aug 13.
A large scale study about energy expenditure has surprisingly showed that human metabolism peaks at about age one and only declines after the age of 60. There are no related changes at either puberty or the menopause, or after childbirth, which as many of us recognise, are key life stages when we all tend to put on weight, or more precisely for many of us, body fat.
The researchers measured the calories burned by 6,600 people aged from one week to 95 years old. They used the state of the art doubly labelled water technique to measure energy expenditure as they went around their daily lives in 29 countries.
Energy expenditure is highest in the first year of life compared to body mass. Then metabolism slows by about 3 per cent per year until you reach around 30. It then levels off. It only starts to decline after the age of 60. Even then this is only at a rate of 0.7 per cent per year.
This study suggests that the drivers of changes in metabolism are cellular changes unrelated to different stages of life.
My comment: So, for the most part we can’t blame our metabolisms for slowing down for our weight gain at various stages of life. The big gain times seem to me to be puberty, moving to university, pregnancy and after having a baby, the mid-forties and peri-menopause years, and retirement.
So what are the causes? I would say these are hormonal and lifestyle related.
Puberty is characterised by hormonal surges, appetite stimulation, and for girls in particular a reduction in active games and sport in preference to socialising. In pregnancy the appetite is stimulated and in my case, if I didn’t eat solid food every 3 hours day and night between weeks 10 to 20, I would vomit for hours. I had to set my alarm through the night and ate loads of breakfast cereal and milk, even keeping it in my car!
When students go to university and when they become exhausted new parents the lure of the quick fix carry out meal and sugary/alcoholic drinks becomes stronger.
The onset of the menopause reduces oestrogen and this leads to cortisol being less inhibited. Chronic stress and sleep deprivation, also enhance cortisol excretion and this stimulates the appetite and belly fat accumulation.
Retirement for many can prompt a resurgence of walking, golf and keep fit activities but also may lead to less activity if the job or commute involved a lot of walking or stair climbing.
Since we can’t just blame our metabolisms any more, we do need to consider what lifestyle changes we can make that will keep us slim and fit.