Could a cup of coffee aid weight loss or help prevent type 2 diabetes? It’s a possibility, according to scientists at the University of Nottingham School of Medicine, and Wolfson Centre for Stem Cells, Tissue Engineering and Modelling (STEM). The researchers have found that the caffeine in our coffee, tea, and colas directly activates a kind of body fat called brown adipose tissue (BAT), which burns calories to generate heat. Results from their studies in cell models and in human volunteers indicate that caffeine could feasibly be included in strategies against obesity and metabolic disorders such as type 2 diabetes.
“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,” said research co-lead Michael Symonds, PhD, at the University of Nottingham School of Medicine. “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.”
Symonds and colleagues report their findings in Scientific Reports, in a paper titled, “Caffeine exposure induces browning features in vitro and in vivo.”
The bodies of humans and other mammals contain two types of fat. White adipose tissue (WAT), or white fat, is laid down to store excess energy taken in as calories. Brown fat was originally discovered in babies and in hibernating animals, and generates body heat by burning calories. Brown fat activation is characterized by increased function of the BAT-specific uncoupling protein 1 (UCP1) in mitochondria.
“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,” Symonds explained. “Increasing its activity improves blood sugar control as well as improving blood lipid levels and the extra calories burnt help with weight loss. However, until now, no one has found an acceptable way to stimulate its activity in humans.”
The amount of brown fat in adult humans diminishes with age, and is also negatively correlated with increasing body mass index, so it is feasible that changing the rate of BAT loss could have “marked benefits for human health,” the authors continued. “Enhanced BAT activity in adult humans has the potential to improve lipid and carbohydrate homeostasis as well as contributing to weight loss strategies … This could be achieved through dietary ingredients but, although it has been shown that diet can stimulate BAT function, the extent to which individual nutrients can have comparable effects is not well established.”
The plant alkaloid caffeine (1,3,7-trimethylxanthine) is found widely in coffee, tea, and cola drinks, as well as in chocolate. Previous research has suggested that caffeine consumption can help weight loss and boost the body’s energy expenditure. Caffeine intake has also been associated with reduce risk of type 2 diabetes, but the extent to which caffeine—or coffee—may directly activate brown fat isn’t known.
Using a well-recognized mouse mesenchymal stem cell (mMSC) model of browning, the researchers first confirmed that caffeine could directly enhance UCP1 function, and so ramp up mitochondrial activity and lipid handling. Cells exposed to caffeine demonstrated more numerous, densely packed mitochondria, and increased mitochondrial division. Caffeine also enhanced cell respiration, increased glycolysis and oxidative phosphorylation, “indicative of more metabolically active cells.”
The team identified a physiologically relevant dose of caffeine that they could test out in humans, and then carried out a series of studies in nine healthy adult men and women with a normal BMI, to see if caffeine consumption stimulated brown fat activation.
Using a thermal imaging technique that they had previously developed to visualize brown fat reserves, the team saw that caffeine consumption significantly increased the temperature in an area around the neck that carries the primary store of brown fat in adults. “The increase in temperature of the region which co-locates with BAT observed with caffeine ingestion is indicative of an increase in BAT activity following a relatively low dose of caffeine from a single standard cup of coffee,” they wrote. “These findings suggest that the increase in metabolic rate following caffeine ingestion could be mediated by enhanced BAT function, which precedes any change in skin temperature.”
“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,” explained Symonds. “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 program to help prevent diabetes.”
“In conclusion, these results provide new complementary in vitro and in vivo evidence that caffeine (and a coffee beverage) can promote BAT function at doses compatible with human use,” the researchers concluded. “Enhanced BAT activity in adult humans has the potential to improve lipid and carbohydrate homeostasis as well as contributing to weight loss strategies.” They acknowledge that more research will be needed to see if the effects are dose-dependent, and whether caffeine could have clinical use against metabolic disorders such as diabetes or obesity. “Future intervention studies can now be undertaken to assess whether caffeine-induced BAT activation in humans is dose-dependent, refine the minimal intake required for a BAT response, and explore whether comparable effects are seen in fully differentiated adipocytes and primary cells, as well as in diabetic and/or obese individuals.”