Exactly when you were born could play a hidden role in your future BMI

Daily Mirror

05-06-2025

Eating well, exercising regularly and maintaining a clean-living lifestyle are key to keeping your weight healthy but new research suggests a different factor could affect BMI
Known as BMI, Body Mass Index is the calculation that uses your height and weight to estimate your body fat. Staying within the right weight range is said to lower your risk for serious conditions such as heart disease, high blood pressure and type 2 diabetes - and the way to do it is typically focused on diet, exercise and lifestyle.
Prioritising getting enough sleep and avoiding stress, consuming nutrient-rich foods and engaging in physical activity are thought to be the key to maintaining a healthy BMI. But a new study has found another factor that could come into play - and there's nothing you can do about it.
Research published in the journal Nature Metabolism explored the link between weather conditions and a person's physiology over the course of their life and an intriguing result emerged.
People conceived during colder months, researchers found, could end up with a lower BMI and less fat around their internal organs, the Independent reported.
The study from Japan 's Tohoku University looked at 683 healthy men and women aged between three and 78 and found those conceived during a cold season ended up with 'higher brown adipose tissue density'. Brown fat tissue generates heat to help the body maintain its core temperature, including in newborns and cold environments.
Higher density of the tissue has been linked to a lower internal fat accumulation into adulthood, meaning people conceived during a cold season could end up with a lower BMI.
By contrast to brown adipose tissue, white adipose tissue is the most abundant type of fat in the body. Research found when it gets colder, less of this is stored than under hotter conditions.
"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," said researchers in the study.
"Lower outdoor temperatures and greater fluctuations in daily temperatures during the fertilisation period are key determinants of brown adipose tissue activity." they added.
Obesity is a key risk factor for death, with more than a billion people around the globe thought to be living with very high levels of body fat. You're considered to be obese if you're 20 per cent over your healthy weight range.
Key advice to lower your BMI includes:
1. Do at least five half-hour sessions of moderate activity every week, such as brisk walking.
2. Eat five portions of fruit and veg a day. Besides being low in fat, they contain antioxidants, which help prevent serious illness.
3. Drink no more than two to three units of alcohol per day for women (and a weekly limit of 14). A unit equals half a pint of beer, a small glass of wine or a single measure of spirits.
4. Limit takeaways to once or twice per month. They are full of saturated fat, which raises the risk of high blood pressure and cholesterol - both of which are major risks for heart disease.