Both exercise and cold burn fat, but how?

Why is physical exercise so beneficial to our health? A new study reveals part of the answer, as a fat molecule — which improves cardiometabolic health — is found to be released during exercise.

Physical activity and our heart and metabolic health are known to be intimately linked. Even the slightest increase in physical activity levels lowers cardiometabolic risk, studies have shown, while less physical activity raises the risk of cardiovascular disease and diabetes. But why is exercise so good for our body, and how does it help us to manage fat levels and keep a healthy weight?

Researchers at the Joslin Diabetes Center — affiliated with Harvard Medical School in Boston, MA — in collaboration with scientists at the Ohio State University in Columbus set out to investigate.

The researchers found that even a short, moderate bout of exercise boosts the levels of a key lipid that is released by brown fat, or the "good" type.

Brown fat is considered to be "good" because, unlike white fat — which has been tied to conditions such as heart disease and diabetes — it burns calories; the main purpose of brown fat is to convert the food we eat into energy.

The new findings — which are now published in the journal Cell Metabolism — "highlight another mechanism for the beneficial effects of exercise," explains study co-author Laurie Goodyear, a senior investigator at the Joslin Diabetes Center.

Cold and exercise have similar effects

The lipid in question is called 12,13-dihydroxy-9Z-octadecenoic acid (or 12,13-diHOME), and one of the interesting things about it is that our body also releases it when we're cold. Previous research has shown that exposure to cold makes the lipid 12,13-diHOME stimulate brown fat activity, and that people with a higher level of 12,13-diHOME have better insulin sensitivity and a lower body mass index (BMI).

What the new study found, for the first time, is that exercise also boosts 12,13-diHOME levels. Using lipidomics analysis, the researchers saw that a single "bout of moderate-intensity exercise causes a pronounced increase in the circulating lipid [12,13-diHOME] in male, female, young, old, sedentary, and active human subjects."

An additional examination of mice revealed that in rodents, too, both a short bout of exercise and long-term physical training boosted levels of the lipid. Finally, removing the rodents' brown fat canceled this effect, confirming the fact that the lipid is produced by this type of fat.