Blame the calendar? How your birth month may shape your body fat

High blood pressure, high cholesterol, obesity, and diabetes have all seen a sharp rise since the mid-1900s.

These health issues are generally associated with factors like poor diet and lack of physical activity.

But have you ever wondered whether your body fat may not entirely be within your control?

New research now shows that the month in which you are born might play a role in shaping your body’s health as you age.

In this explainer, we explore how birth month could affect body fat levels over time and what the latest findings reveal.

How your birth month impacts body fat

Scientists have found that people conceived during the colder months tend to have more active brown fat, a kind of fat that helps the body stay warm by burning calories.

This kind of fat helps the body use more energy, lowers body mass index (BMI) , and reduces fat stored around organs.

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A new study, published last week in ‘Nature Metabolism’, looked into how weather conditions at the time of conception may affect health later in life.

Researchers at Tohoku University Graduate School of Medicine studied the temperature and environment during the time of conception.

They found that those conceived in winter months, typically December to February, had more active brown fat. As a result, they managed to burn more calories and had lower levels of fat around their organs.

If you were born in September, October or November, it is likely you were conceived in winter and may benefit from this effect, the study says.

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Meanwhile, those born in April and May, likely conceived in the hot summer months of July and August, may not see the same benefits.

“Our study suggests that the environment experienced by parents even before pregnancy can shape the child’s metabolic health later in life,” study author Takeshi Yoneshiro, a metabolism researcher at Tohoku University, told Popular Science.

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What is brown fat? What did the study conclude?

Yoneshiro and his team found that people conceived during colder months tend to have more brown fat.

This brown fat, or brown adipose tissue (BAT), is different from white fat, which stores energy and contributes to weight gain. While adults have small amounts of brown fat in areas like the neck, shoulders and back, newborns have much more of it to help keep warm.

Brown fat becomes more active when exposed to the cold. For instance, cold water immersion is known to trigger this activity, which helps burn calories.

Writing in ‘Nature Metabolism’, the researchers say the activity of brown fat may be set even before a baby is conceived, influenced by cold weather. Interestingly, they believe this may be more connected to the father’s exposure to low temperatures than the mother’s.

Previous studies have suggested that cold conditions could affect sperm, leaving a kind of memory that gets passed on at conception. This could help the embryo grow with better metabolism and temperature control.

To explore this further, the Japanese researchers studied 683 healthy participants, aged between three and 78. They were split into two groups based on when they were conceived: those whose parents experienced cold weather around the time of conception (from 17 October to 15 April), and those conceived during warmer months (16 April to 16 October).

Their analysis showed that people from the colder group had higher brown fat activity. This was linked to greater calorie use, better temperature regulation, less fat around vital organs and lower BMI even into adulthood.

“Here we report that individuals whose mothers conceived during cold seasons exhibit higher brown adipose tissue activity, adaptive thermogenesis, increased daily total energy expenditure and lower body mass index and visceral fat accumulation,” the researchers wrote.

They concluded that brown fat activity is mostly shaped by the weather before conception, especially colder average temperatures and large day-to-day shifts in outdoor conditions.

The researchers say further work is needed to understand why this happens. They hope to look into how food and other environmental conditions may also play a role.

Obesity in India

India had the second-largest number of overweight or obese adults in 2021, with 18 crore people affected, second only to China.

A study published in ‘The Lancet’ in March warns that this figure could rise to 45 crore by 2050, making up nearly one-third of the country’s estimated population.

The study also projects that, globally, over half of all adults and one in three children and teenagers could fall into the same category.

In 2021, an estimated 211 crore people, around 45% of the world’s population, were either overweight or obese.

Nearly half of these individuals were concentrated in eight countries: China (40.2 crore), India (18 crore), the United States (17.2 crore), Brazil (8.8 crore), Russia (7.1 crore), Mexico (5.8 crore), Indonesia (5.2 crore), and Egypt (4.1 crore), The Indian Express reported.

The number of adults aged 25 and older diagnosed as ‘overweight’ or ‘obese’ in India increased from 1990 to 2021.