Ah, the circle of life! Your parents have sex, and nine months later, you arrive into the world (apologies for that image).
But did you know that the temperature around the time of your parents’ hanky-panky might impact your metabolism for the rest of your life?
At least, that’s according to a recent study by researchers at the University of Tokyo, Japan.
They calculated the season during which 642 Japanese adults were conceived and found that those whose parents ‘did it’ during colder months were more likely to have a lower body mass index (BMI), less visceral (abdominal) fat and faster metabolism than those conceived in summer.
This is all to do with brown fat: a type of fat that burns energy even when we’re resting, keeps us warm in the cold and helps the body regulate blood sugar.
“People conceived during cold seasons tend to have more active brown fat as adults, which helps burn calories and generate heat,” lead author Takeshi Yoneshiro, associate professor at Tohoku University Graduate School of Medicine, told BBC Science Focus.
If we have more active brown fat, our bodies burn more energy when we’re resting – which might mean we have a faster metabolism than someone with less active brown fat.
Professor Jaswinder Sethi, an immunometabolism specialist at the University of Southampton, who was not involved in this research, told BBC Science Focus: “The primary function of brown fat is to generate heat and keep the body warm.
“But the activity of brown fat contributes significantly to energy expenditure. In doing so, it helps reduce the amount we need to store, thereby preventing overweight or obesity and risks of developing metabolic diseases.”
Yoneshiro explained that our parents’ exposure to the cold might lead to epigenetic changes – meaning, alterations to how our genes are expressed – that give us more brown fat, so we’re better adapted to wintry climates.
“In modern times, with heating systems and air-conditioning, this metabolic system seems to be useful for regulating energy balance and preventing metabolic diseases,” said Yoneshiro.
But Sethi said: “It is important to note that, like the majority of genetic variations known to be linked to obesity, these changes may only predispose individuals to altered metabolism, so they are unlikely to be the sole factor causing disease later in life.”
And Dr Adam Collins, associate professor of nutrition at the University of Surrey – who was also not involved in this research – told BBC Science Focus that brown fat might not be all that important for regulating metabolism.
“It might not be that people who have more brown fat will have a higher metabolic rate,” he said. “They’ll probably just be more cold-tolerant, because energy wasting from brown fat – which everybody thinks is great – is deliberately for generating heat. It's not for wasting calories.”
This study was only observational, so it can’t prove that ‘winter loving’ causes faster metabolism in children.
But Yoneshiro said: “If other stimuli can replicate this effect, we may be able to develop targeted interventions to promote metabolic resilience in the next generation.”
Read more:
- Why it's time we changed our relationship with fat
- How to boost your metabolism: 5 simple ways to speed up fat loss
- The fast metabolism myth: Here’s what actually determines how slim you are
About our experts:
Dr Takeshi Yoneshiro is an associate professor of biomedical science at Tohoku University's Graduate School of Medicine, in the Division of Molecular Physiology and Metabolism. Before joining Tohoku University in 2023, he was an associate professor at the University of Tokyo, in their Research Centre for Advanced Science and Technology.
Jaswinder Sethi is a professor of immunometabolism at the University of Southampton. She is also an Honorary NHS Foundation Trust Research Fellow and a member of the Institute for Life Sciences. Her research interests include immunometabolism, obesity, metabolic diseases and tissue remodelling.
Dr Adam Collins is an Associate Professor of Nutrition at the University of Surrey's School of Biosciences. He has been a qualified nutritionist for more than 20 years and is a programme leader for BSc and MSc nutrition at Surrey. His current research includes exercise intensity and energy balance, intermittent fasting, meal timing and composition – specifically, the use of carbohydrate manipulation for metabolic health.
