Scientists made the discovery after studying 34 commonly used pesticides and herbicides in brown fat cells and testing the effects of chlorpyrifos in mice fed high-calorie diets. Their findings were published in Nature Communications and could have important implications for global public health.
“Brown fat is the metabolic furnace in our body, burning calories, unlike normal fat that is used to store them. This generates heat and prevents calories from being deposited on our bodies as normal white fat. We know brown fat is activated during cold and when we eat,” said senior author Gregory Steinberg, professor of medicine and co-director of the Centre for Metabolism, Obesity, and Diabetes Research at McMaster.
For this study, mice were exposed to 2.0 mg/kg body weight of chlorpyrifos daily, a dose that is equivalent to the real-world exposure of humans. Steinberg said that, while chlorpyrifos has been linked to rising obesity rates in both humans and animals, most of these studies have attributed weight gain to associated increases in food intake and not to the suppression of metabolism in the brown fat cells.
“Lifestyle changes around diet and exercise rarely lead to sustained weight loss. We think part of the problem may be this intrinsic dialling back of the metabolic furnace by chlorpyrifos.”
Steinberg said chlorpyrifos would only need to inhibit energy use in brown fat by 40 calories every day to trigger obesity in adults, which would translate to an extra five lbs of weight gain per year. Mice that developed obesity in this study due to exposure also showed an increased incidence of insulin resistance and non-alcoholic fatty liver disease.
He said that while several environmental toxins including chlorpyrifos have been linked to rising obesity rates in both humans and animals, most of these studies have attributed the weight gain to increases in food intake and not the burning of calories.
It was only discovered recently that adult humans have brown fat, which is switched on when eating, previously thought to only exist in infants and other animals, and that people with obesity have lower brown fat activity, said Steinberg.
While the use of chlorpyrifos on foods is banned in Canada, imported produce may still be treated with it.
“Although the findings have yet to be confirmed in humans, an important consideration, is that whenever possible consume fruits and vegetables from local Canadian sources and if consuming imported produce, make sure it is thoroughly washed,” said Steinberg.
