Letter: We and our microbiome can have diet advice (2)

From William Meggs,Greenville, North Carolina, US

Wilson correctly points out the limitations and inconsistencies of observational studies based on questionnaires, and the inability to perform randomised controlled studies of diet and health. She concludes that the problem is serious enough that we should be sceptical of all dietary advice.

But there are studies that examine health differences in geographical populations with different diets: for instance, those comparing northern European populations that typically consume more animal-based fats with southern European populations whose diets feature fish, vegetables and olive oil.

Other studies compared the health of Japanese immigrants to the US who adopted typically lower-quality American diets with those in Japan who followed a traditional diet.

Studies comparing vegetarians with meat eaters support the value of a vegetarian diet.