Ah, the circle of life! Your parents engage in intimate activities, and nine months later, you make your grand entrance into the world (apologies for that mental image).

However, did you know that the temperature during your parents’ romantic encounters could impact your metabolism for the long haul?

According to recent research conducted by a researcher at the University of Tokyo in Japan, this might be the case.

The study analyzed the season when 642 Japanese adults were conceived and discovered that individuals conceived during colder months tend to have lower body mass index (BMI), less visceral (abdominal) fat, and a faster metabolism compared to those conceived in warmer months.

This correlation is linked to brown fat, a type of fat that burns energy even at rest, helps keep the body warm, and assists in regulating blood sugar levels.

“People conceived during colder seasons tend to have more active brown fat as adults,” explained Takeshi Yoneshiro, an associate professor at Tohoku University Graduate School of Medicine, in an interview with BBC Science Focus.

Having more active brown fat means the body burns more energy while resting, potentially resulting in a faster metabolism compared to individuals with lower levels of brown fat.

Professor Jaswinder Sethi, an expert in immuno-metabolism at the University of Southampton who was not involved in the research, stated to BBC Science Focus: “Brown fat’s primary role is to produce heat and maintain body temperature.

“Moreover, brown fat activity significantly contributes to energy expenditure, aiding in reducing the need for storage and potentially preventing the risk of obesity and metabolic disorders.”

Yoneshiro suggested that parental exposure to cold temperatures could lead to epigenetic modifications, influencing how our genes are expressed.

“In modern times, this metabolic system may help regulate energy balance and protect against metabolic diseases by acting as a heater and air conditioner,” Yoneshiro explained.

However, Sethi cautioned: “It’s crucial to note that, similar to many known genetic variations associated with obesity, these changes are not the sole contributors to future health issues, as individuals may have genetic predispositions affecting their metabolism.”

Additionally, Dr. Adam Collins, an Associate Professor of Nutrition at the University of Surrey not involved in the study, stated to BBC Science Focus that the significance of brown fat in metabolic regulation may be overemphasized.

“Having abundant brown fat might not necessarily equate to a higher metabolic rate,” Collins noted. “The benefit of brown fat lies in its ability to generate heat, particularly in cold conditions, rather than simply burning calories.”

Since this study is observational, it cannot definitively prove that the season of conception impacts a child’s metabolism in the long term.

Nonetheless, Yoneshiro expressed hope: “If other factors can reproduce this effect, targeted interventions may be developed to enhance metabolic resilience in future generations.”

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About our experts:

Dr. Takeshi Yoneshiro is an associate professor of biomedical sciences specializing in molecular physiology and metabolism at Tohoku University’s Graduate School of Medicine. Prior to joining Tohoku University in 2023, he served as an associate professor at the Center for Advanced Science and Technology Research at the University of Tokyo.

Jaswinder Sethi is a professor of immunotherapy at the University of Southampton. She is also an Honorary NHS Foundation Trust Research Fellow and a member of the Life Sciences Institute. Her research focuses on immune metabolism, obesity, metabolic diseases, and tissue remodeling.

Dr. Adam Collins is an Associate Professor of Nutrition at the School of Biological Sciences, University of Surrey. With over 20 years of experience as a qualified nutritionist, he leads BSc and MSc nutrition programs at the university. His research includes studying exercise intensity and energy balance, intermittent fasting, dietary composition and timing, and carbohydrate manipulation for metabolic health.