Commentary: Should you eat meat, or are you confounded by methodological debate?

Selection

The non-meat eaters were volunteers, mainly recruited through advertisements and word of mouth in an organisation that promotes vegetarianism. Such volunteers will differ greatly from the general population, not only in age and sex, but also in education, social class, and other aspects of lifestyle. To counter these obvious objections the authors asked the non-meat eaters to recruit friends or relatives as controls. These people ate meat more regularly but belonged to the same social strata and might also have shared other habits.

As expected, the overall and cause specific mortalities were lower in both groups than in the general population. The reduction in mortality was greater among the non-meat eaters. There is, however, a possibility that the two groups were not comparable and that the “healthy person effect” might have been operating. People who are enthusiastic about their vegetarian life may have volunteered to prove how healthy vegetarianism is. Their meat eating …