Short-term exposure to low temperatures activates the so-called brown adipose tissue, which burns calories in humans. However, scientists from Leiden University in the Netherlands learned that the effectiveness of this type of calorie burning depends on the time of day. The study was presented at the European Society for the Study of Obesity Congress.
Brown fat or brown adipose tissue is a special type of fat that is activated in response to low temperatures. Its main role is to generate heat to maintain body temperature, and this is achieved by burning calories, especially from fat.
Therefore, exposure to the cold in the morning may be more effective at speeding up metabolism and burning fat in men, but not in women. They got the highest result, on the contrary, it was recorded in the evening.
The researchers conducted a randomized crossover study with 24 adults, 12 men and 12 women. Participants were randomized to a 2.5-hour individual cooling session using mattresses filled with water in the morning (7:45) and evening (19:45).
The water temperature was gradually lowered until shaking was observed or until a temperature of 9°C was reached. Participants were then exposed to continuous cold for an additional 90 minutes. During this time, the researchers measured energy expenditure and skin temperature four times during the experiment.
The analysis showed that cold-related energy expenditure and skin temperature (both indicators of brown fat activity) in men were higher in the morning than in the evening. Cold-related energy expenditure and skin temperature were not different in women, but they were more tolerant to cold in the morning than in the evening. Therefore, the effectiveness of such treatment in the evening is higher.