, he discussed a study he had co-authored and said: “The single most important dietary factor we found for better gut health was the number of different plants we eat weekly, with 30 a week being the optimal number.”
The number of 30 plants per week is entirely arbitrary and was chosen by the researchers. It didn’t come out of the data and is rather a convenient number to represent “people who eat a large number of plants”. We have no idea whether people who ate, say, 20 plants per week, or 15, would see the same benefits. The specific number of 30 doesn’t mean anything at all.
The “number of plants” measure was also self-reported on a questionnaire , making it very vulnerable to the participants forgetting, misunderstanding the question, or justThe questionnaire included many dozens of questions on diet, too, and asked how often the participants ate fermented food, dairy, sugary snacks, artificial sweeteners, and much more. It’s not immediately clear why they only focused on the low and high extremes of the answers to that single question about plants.