Having high levels of caffeine in your blood may lower the amount of body fat you carry and reduce the risk of type 2 diabetes, research suggests. The findings could lead to calorie-free caffeinated drinks being used to reduce obesity and type 2 diabetes, though further research is required, the researchers wrote in the BMJ Medicine journal. Dr Katarina Kos, a senior lecturer in diabetes and obesity at the University of Exeter, said the research showed potential health benefits for people with high levels of caffeine their blood, but added: “It does not study or recommend drinking more coffee, which was not the purpose of this research.” She said any caffeinated drinks containing sugar and fat would offset the positive effects. The researchers said their work built on previously published research, which suggested that drinking three to five daily cups of coffee, containing an average 70-150mg of caffeine, was associated with a lower risk of type 2 diabetes and cardiovascular disease. As those were observational studies, they made it difficult to pinpoint whether the effects were because of caffeine or other compounds, the researchers said. This latest study used a technique known as Mendelian randomisation, which establishes cause and effect through genetic evidence. The team found two common gene variants associated with the speed of caffeine metabolism, and used these to work out genetically predicted blood caffeine levels and whether this was associated with lower BMI and body fat. People who carry genetic variants associated with slower caffeine metabolism drink less coffee on average, yet have higher levels of caffeine in their blood than people who metabolise it quickly. The researchers found that nearly half of the reduction in type 2 diabetes risk was driven by weight loss. Caffeine is known to boost metabolism, increase fat burning and reduce appetite, with a daily intake of 100mg estimated to increase energy expenditure by about 100 calories a day. There are limitations to the findings, including that the research was based on nearly 10,000 people of predominantly European ancestry, who were taking part in six long-term studies. Dr Stephen Lawrence, an associate clinical professor at the University of Warwick’s medical school, said the study was “interesting” and used “good science”, but noted that the Mendelian assessment was a “relatively new technique” and, although useful, was “vulnerable to bias”. He said it could lead to future studies that could eventually develop promising treatments. “This represents good hypothesis-forming or idea-forming science. It does not, however, prove cause and effect. We therefore need to be cautious not to rush to over-interpret it.” The authors made a “big leap of faith” in assuming that the weight loss brought about by increased caffeine consumption would reduce the risk of developing type 2 diabetes, Lawrence said, adding that it was not more effective than reducing calorie intake and increasing physical activity. Additionally, caffeine consumption gave some people palpitations and abnormal heart rhythms, so it was not suitable for everyone. He said: “Should people drink more coffee to reduce fat or diabetes risk? The science suggests relatively good evidence that consuming caffeine increases fat burning, even at rest. However, it does not constitute a treatment for obesity and, used wrongly, may result in weight gain or even harm.”