According to a study presented at the European Congress on Obesity (ECO) held in Dublin, brief exposure to cold temperatures activates brown fat. This leads to the burning of calories, which has become a prominent target to promote cardiometabolic health.

In the preliminary study conducted by Dr. Maritte Boon and colleagues from the Leiden University Medical Centre in the Netherlands, it was found that exposure to cold in the morning can boost metabolism and burn fat more efficiently than exposure to cold in the evening in men. However, the same was not observed in women.

Brown fat, also known as brown adipose tissue (BAT), is a form of fat that becomes activated in response to low temperatures. Its principal function is to generate heat to help maintain body temperature, which it accomplishes by burning calories, particularly fat calories.

The researchers conducted a randomized crossover study that included 24 lean adults. The participants were from the age group of 18 to 31 years old, with a BMI in the range of 18–26 kg/m2. For the study, the participants underwent a 2.5-hour personalized cooling protocol using water-filled mattresses in the morning and evening, in random order.

The temperature of the water was steadily reduced until shivering occurred or a temperature of 9°C was obtained. After that, participants were exposed to steady cold for another 90 minutes.

During the experiment, researchers measured energy expenditure (via indirect calorimetry) four times, i.e., at the start under thermoneutral conditions (at 32°C, when the body does not need to produce extra heat to maintain its core temperature), during the cooling down phase, during the stable cold phase, and at the end of cooling (after 90 minutes). The temperature of the supraclavicular skin was also recorded regularly using infrared thermography.

The findings of the study showed that cold-induced energy expenditure and skin temperature were higher in the morning than in the evening in men. However, in females, cold-induced energy expenditure and skin temperature did not differ between the morning and the evening.

It was also observed that females were more tolerant of cold in the morning than in the evening. Moreover, in women, circulating free fatty acid concentrations, triglycerides, and cholesterol levels were higher after cold exposure in the morning than in the evening. 

(Source:https://theprint.in/health/study-discovers-how-time-of-day-determines-effectiveness-of-cold-exposure-in-fat-burning/1587174/ )