This month the World Health Organisation announced that eating red meat is an activity fraught with risk, and shoppers in the UK at least are taking no chances. Three weeks after the WHO announced that processed meats are on par with cigarettes as a “convincing” cause of cancer, British sales of packaged sausages were down by about 16 per cent. But the WHO overstates its case, in a way that could even create risks of its own.

There are three ways to tell whether a substance causes cancer. The first, which cannot be relied on alone, is to see whether there is a plausible biochemical mechanism leading from exposure to malignancy. Here, the WHO thought the evidence was moderate to strong. The second kind of evidence, animal testing, gave no grounds for concern. Feeding animals a diet rich in red meat does not give them cancer.

So the WHO leaned heavily on the third source: epidemiological data. Its great success was in linking smoking to cancer. In that case, smokers faced a risk of contracting lung cancer between nine and 25 times greater than did non-smokers. Unless relative risks are greater than five, epidemiological studies typically provide only low-quality evidence. The decision on meat was based on relative risks of just 1.17 to 1.18. Look at the population as a whole, and the lifetime risk of contracting colon cancer is less than 4.5 per cent. A relative risk of 1.17 raises that only to 5.3 per cent.