Metabolism Changes with Age, But Not How We Think

A new study has blown everything we know about metabolism out of the water. We know the basics. Our metabolism slows down in middle age. Men have a faster metabolism than women. Women’s slow down even more after menopause. Well, no. It’s all wrong, according to a massive study that many call groundbreaking.

It will be in textbooks,” said Leanne Redman, an energy balance physiologist at Pennington Biomedical Research Institute. She also called it “a pivotal paper.”

That’s because the new study is so different. It redefines our understanding of how the body works and could change practical things — like what drug doses doctors prescribe older people and children. Using 6,500 people aged between eight days and 95 years, they found that we have four stages of life for our metabolism. They also found that there’s no distinguishable difference between men and women.

Research on metabolism is really expensive. So, usually, studies are very small. In this case, labs agreed to pool all of their data. The study has 80 authors and research collected over 40 years, showing how bodies change throughout life. Over those decades, they were all tracking how many calories people were burning through how much carbon dioxide they exhaled during their normal days.

They found that from birth to the age of one, the metabolism is the fastest, 50 percent faster than the adult rate. From age one to 20, the metabolism slows by three percent a year. From 20 to 60, it remains the same. And after 60, it drops by about 0.7 percent annually. There was no difference between men and women of the same size and weight.

Learning that babies have a fast metabolism makes sense. They grow and develop so quickly. But, the scientists said that their metabolism seemed to outstrip the speed of their growth. “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,” said study co-author Herman Pontzer, associate professor of evolutionary anthropology at Duke Univ. “Something is happening inside a baby’s cells to make them more active, and we don’t know what those processes are yet.”

The fact that men and women were the same and that people between the ages of 20 and 60 maintain the same metabolism goes against years of commonly held beliefs. The researchers were shocked to see that menopause made no difference to metabolism. And that gender didn’t play a role. On average, adults gain more than a pound and a half a year. This has always been attributed to a slowing metabolism. But it isn’t true. Reviewing it, doctors said the real problem is simple: people eat more calories than they can burn, metabolism has nothing to do with it. If there is excess, then there’s excess.

It’s going to take a lot of mental adjustments to come to terms with these finds. The old way of thinking just made sense. “There are lots of physiological changes that come with growing up and getting older,” said Prof. Pontzer. “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.”

We think this study is fascinating and could impact medicine. But what we take away from it for our personal lives is the importance of a healthy diet and exercise. We cannot depend on any metabolism tricks to get us through. We have written about plenty of foods that claim they speed up the metabolism. Nutritionists swear some will boost your metabolism. While we don’t doubt their earnest belief, this shows that science is still developing. We always stress the importance of variety and balancing your diet with a healthy lifestyle and exercise. This underscores that for us. No one aspect of health can be banked upon, so it’s best to have a multitude of healthy habits that build up to a better life.  

Banner image: Patrick Jansen via Unsplash

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