Drinking coffee could help boost weight loss, researchers say.
Experts found that drinking a cup of coffee can stimulate "brown fat", which burns calories to generate body heat.
Professor Michael Symonds, from the School of Medicine at the University of Nottingham, who co-directed the study, said this was the first research to show how coffee has an impact on brown fat in humans.
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He said: "Brown fat works in a different way to other fat in your body and produces heat by burning sugar and fat, often in response to cold.
"Increasing its activity improves blood sugar control as well as improving blood lipid levels and the extra calories burnt help with weight loss.
"This is the first study in humans to show that something like a cup of coffee can have a direct effect on our brown fat functions.
"The potential implications of our results are pretty big, as obesity is a major health concern for society and we also have a growing diabetes epidemic and brown fat could potentially be part of the solution in tackling them."
Researchers, writing in the journal Scientific Reports, first used stem cells to see if caffeine would stimulate brown fat.
They then moved on to humans, using a thermal imaging technique to trace the body's brown fat reserves as they emitted heat.
Prof Symonds said: "From our previous work, we knew that brown fat is mainly located in the neck region, so we were able to image someone straight after they had a drink to see if the brown fat got hotter.
"The results were positive and we now need to ascertain that caffeine as one of the ingredients in the coffee is acting as the stimulus or if there's another component helping with the activation of brown fat.
"We are currently looking at caffeine supplements to test whether the effect is similar.
"Once we have confirmed which component is responsible for this, it could potentially be used as part of a weight management regime or as part of glucose regulation programme to help prevent diabetes."
Brown fat - also known as brown adipose tissue (BAT) - differs from "white fat" in the body, which occurs as a result of excess calories.
Experts say people with a lower body mass index (BMI) tend to have a higher amount of brown fat.