Born to Burn Fat? When You Were Conceived May Impact Your Metabolism, Study Reveals

Everyone’s metabolism works a little differently—and surprisingly, a new study suggests that your metabolism and body fat levels may be influenced by the season you were conceived. In other words, environmental conditions like outdoor temperature at the time of fertilization might affect how your body stores and burns fat years later.

What the study says about conception season and body fat

A recent study published in Nature Metabolism (the largest of its kind) found that men who were conceived during colder months store fat differently from those conceived in warmer months.

Participants included 356 healthy young male volunteers, and researchers in Japan exposed them to a chilly 19 °C (66 °F) for two hours. Brown fat activity and metabolic activity were assessed after cold exposure and again after sitting at room temperature. 

Researchers found that those who were conceived in a cold season showed relatively higher rates of brown adipose tissue, which is a type of fat that burns energy and assists blood sugar regulation. People who are deemed overweight or obese often have less brown fat activity. 

More specifically, brown fat activity was notably higher in those who were conceived in the Northern Hemisphere between January 1 and April 15 and October 17 and December 31, as opposed to those conceived in a warm period between April 16 and October 16.

This group also showed increased energy expenditure, a lower body mass index (BMI), and less fat accumulation around their organs, indicating better metabolic health overall. 

Can these findings apply to women, too?

To extend the results to a wider population, researchers analyzed a second cohort of 286 male and female adults of various ages. Ultimately, they found “modest yet significant associations” between conception during cold seasons and brown fat activity. Also detected in this group was decreased BMI, waist circumference and visceral fat, which surrounds your internal organs. 

Scientists believe that the increase in brown adipose tissue (BAT) activity is what is driving the other metabolic outcomes. Individual factors on their own, specifically BMI, were not directly associated with the season of conception.

Important to note: There was no significant link between a person’s birthday and their metabolic health—only with their season of conception, 266 days before birth. Also, the findings in the study do not prove a direct causal relationship but a correlation. 

How temperature at conception may influence metabolism

Study leaders surmise that cold weather may affect the genetic expression of male sperm or female eggs, and these changes could be passed along to offspring during fertilization. 

This could be a “sophisticated predictive cold adaptation” passed through the generations, which better enables offspring to survive in cold climates, according to the authors. 

More research is needed to explore this concept, which authors refer to as “pre-fertilization origins of health and disease.” However, these findings align with past research on mice, which revealed that being exposed to certain weather conditions during preconception can boost the metabolism of offspring. 

When applying this science to human subjects, scientists found that people conceived during cold months were 3.2 percent more likely to possess active brown fat tissue, while their counterparts in warmer months were more likely to lack active brown fat. 

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