Children conceived in winter may have lifelong protection against excess weight

Illustrative photo. Photo: freepik.com

Weight loss is usually explained by a simple formula: you need to burn more calories than you consume. But the human body is not a mechanical system, and energy metabolism occurs differently for everyone. As FitBook.de notes, we can accurately name the influencing factors, but another one probably needs to be added to them.

In addition to body weight, age and gender, peculiarities of digestion and food absorption, as well as physical activity, whether our parents were cold before conceiving us may also play a role. Researchers from Japan claim: a cold climate in the weeks before conception can provide offspring with efficient fat burning for life.

What the researchers studied

A large-scale study, the results of which were published in the scientific journal Nature Metabolism, for the first time demonstrates a link between environmental conditions before conception and a long-term impact on energy metabolism in humans.

The study involved five independent cohorts — a total of 1013 healthy Japanese people, mostly young men.

Researchers determined the estimated period of conception, counting back from the date of birth, and divided participants into two groups:

• cold season — from October 17 to April 15,

• warm season — from April 16 to October 16.

Possible influencing factors were taken into account in the analysis: age, gender, and physical activity. The influence of temperature, humidity, daylight duration, and other factors for 12 months before birth was also analyzed.

The main indicator was the so-called activity of brown adipose tissue (BAT), often simply called brown fat. Unlike regular white fat, which stores energy, brown fat burns it, converting it into heat. Its cells are rich in mitochondria — the "power stations" of the cell. High BAT activity is considered a factor that protects against obesity and metabolic disorders.

Researchers determined BAT density using specialized equipment, assessed changes in energy expenditure under cold and food exposure, and measured participants' total daily energy expenditure. Additionally, a meteorological analysis was conducted to check whether certain weather conditions during fertilization correlated with subsequent BAT activity. The influence of temperature, humidity, daylight duration, and other factors for 12 months before birth was analyzed.

Surprising results

People conceived in the cold season, compared to those conceived in the warm period, demonstrated:

significantly higher brown adipose tissue activity;

greater total energy expenditure in everyday conditions — regardless of height, fat-free mass, and activity level;

lower body mass index indicators, smaller waist circumference, and less fat around internal organs (called visceral fat);

increased energy expenditure at low temperatures (measurements were taken at 19°C);

greater energy expenditure after meals;

a clear link between high BAT activity and low body mass index.

Interestingly, the month of birth did not matter. The climatic background in the weeks before conception proved to be important.

What this means for medicine

The study results suggest that environmental conditions even before pregnancy can program the energy metabolism of offspring. From a medical point of view, the results are very important: programmed brown fat activity can help slow down aging processes, weight gain, and the development of metabolic diseases.

At the same time, new questions arise. Can global warming potentially change the energy profile of the population? And is it possible to purposefully use cold stimuli before conception to improve the health of future generations?

For now, these are only hypothetical scenarios. The study does not provide direct evidence that the effect is transmitted specifically through epigenetic mechanisms — it records a correlation, but does not confirm a causal relationship.

Furthermore, the results have several limitations. All participants were Japanese, so it is unknown whether similar patterns would be found in other ethnic groups. The influence of skeletal muscle on overall energy expenditure is also not entirely excluded. Finally, the temperature of 19 °C, at which measurements were conducted, might be an insufficient stimulus for people with high cold resistance to show maximal brown fat activation.

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