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expert reaction to study looking at blood caffeine level and body fat / type 2 diabetes

A study published in BMJ Medicine looks at plasma caffeine, adiposity, type 2 diabetes, and cardiovascular disease.


Dr Katarina Kos, Senior Lecturer in Diabetes and Obesity, University of Exeter, said:

“The genetic study shows links and potential health benefits for people with certain genes attributed to a faster coffee metabolism as a hereditary trait and potentially a better metabolism. It does not study or recommend drinking more coffee, which was not the purpose of this research. Most importantly, when considering coffee consumption and caffeine containing energy drinks, one must be mindful of the potential negative offset by surplus calories in form of sugar and fat in many of these drinks. Even for the option of increasing the use of calorie free caffeine drinks, a benefit has yet to be proven.”


Dr Stephen Lawrence, Associate Clinical Professor at the University of Warwick’s medical school, said:

“This is a very interesting idea-forming study with some good science. It uses a relatively new technique called Mendelian assessment to investigate whether caffeine consumption can cause weight loss and reduce the future risk of type 2 diabetes The link between obesity and type 2 diabetes is well established with over 90% of people with type 2 diabetes being overweight or obese. However, the technique of Mendelian assessment used by the authors requires caution in its interpretation since it is vulnerable to bias which may influence the result. This represents good hypothesis-forming or idea-forming science.  It does not however prove not cause-and-effect. We therefore need to be cautious not to rush to over-interpret it.

“The authors of the study have acknowledged that this is does not prove cause and effect. It is merely suggestive or hypothesis forming. Such studies are important because they form a bedrock for future studies designed to reduce or minimise any viruses.

“Results from any study may be reported as having “statistical significance”  which is often misinterpreted as a “clinically important” result.  Put simply, statistical significance is a numbers game whereas, clinical significance explores how much those results matters in the day-to-day setting.

“The science tells us that the caffeine consumed in approximately 4 cups of coffee can increase your metabolic rate by 3-11%. The higher your metabolic rate, the easier it is for you to burn fat. This sounds like good news if you’re trying to lose weight and this publication supports existing studies suggesting a link between caffeine consumption and increased fat burn. If you consume several cups of coffee, your body will burn fat at a greater rate than those who do not consume coffee. It is well established that obesity is a strong predictor of type 2 diabetes. Over 90% of people with type 2 diabetes are overweight or obese. If you reduce obesity, you reduce the risk of diabetes.

“The big leap of faith that the authors have made is to assume that the weight loss brought about by increased caffeine consumption is sufficient to reduce the risk of developing type 2 diabetes. On a practical basis, caffeine consumption has not been proven to be a standalone treatment for obesity. Some people will find that the consumption of coffee increases the risk of side-effects, such as palpitations, abnormal heart rhythms. On a practical basis, if you have your coffee with sugar, muffins or biscuits you may even experience weight gain! 

“Reducing daily calorie intake is the most important factor for weight loss. There is a far greater body of good quality evidence showing that the traditional methods of reducing calorie intake and increasing physical activity represent the safest and most effective way of losing weight.

“The authors have accounted for biases but some may be out of their control. They also admit that the studies were performed on a Caucasian population and therefore we do not know whether the effect would be transferred to minority ethnic groups, many of whom have a higher risk of diabetes for a similar level of BMI.

“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. To reduce your risk of diabetes and improve your cardiovascular health, it is important to limit calorie intake (especially of refined foods) and to increase physical activity.”



‘Appraisal of the causal effect of plasma caffeine on adiposity, type 2 diabetes, and cardiovascular disease: two sample mendelian randomisation study’ by Susanna Larsson et al. was published in BMJ Medicine at 22.30 UK time Tuesday 14 March 2023.

DOI: 10.1136/bmjmed-2022-000335



Declared interests

Dr Katarina Kos: “I have no conflict of interest.”

For all other experts, no reply to our request for DOIs was received.


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