Research about what is healthy comes so thick and fast – red meat can appear good for you one week, stroke-inducing the next – that a confused public often struggles to keep up. But a massive new review published on Monday aims to look beyond the latest study by evaluating the available evidence on a range of health topics and giving it a star rating. The US-based Institute for Health Metrics and Evaluation (IHME), which has become a global reference for health statistics, analysed the existing research in 180 areas to find out how much a particular risk factor, such as smoking, is linked to a health outcome, such as lung cancer. The connection between smoking and lung cancer was given the highest five-star rating, as was the link between high blood pressure and heart disease, which means that the evidence is solid and unlikely to change in the future. However, nearly two thirds of the risk-outcome relationships received only one or two stars, suggesting that the proof for a lot of widely believed health advice is weaker than might have been thought. For example, evidence for a connection between eating a lot of unprocessed red meat and having a stroke was given just one star, meaning there was “no evidence of an association”, the study said. The links between red meat and colon cancer, breast cancer, ischaemic heart disease and diabetes were all given two stars. Christopher Murray, IHME director and a senior author of several of the “Burden of Proof” studies published in the journal Nature Medicine, said he was “very surprised at how many of the diet risk-outcome relationships are relatively weak.”