Study shows difference between plant based and animal based diet but hard to say which is really better
Animal based diet rapidly and reproducibly changes human gut microbiome
Long-term dietary intake influences the structure and activity of the trillions of microorganisms residing in the human gut1,2,3,4,5, but it remains unclear how rapidly and reproducibly the human gut microbiome responds to short-term macronutrient change. Here we show that the short-term consumption of diets composed entirely of animal or plant products alters microbial community structure and overwhelms inter-individual differences in microbial gene expression. The animal-based diet increased the abundance of bile-tolerant microorganisms (Alistipes, Bilophila and Bacteroides) and decreased the levels of Firmicutes that metabolize dietary plant polysaccharides (Roseburia, Eubacterium rectale and Ruminococcus bromii). Microbial activity mirrored differences between herbivorous and carnivorous mammals2, reflecting trade-offs between carbohydrate and protein fermentation. Foodborne microbes from both diets transiently colonized the gut, including bacteria, fungi and even viruses.
I like this study because it shows very clear measurable differences and it shows how anti-meat bias makes them search diligently for a link between meat and intestinal problems. Since they consider their model microbiome diet to be a fairly low fat plant based bad-at-hunting-gatherer - they already think the meat is causing microbiome problems (and not the sugar).
I'd like to see better questions explored with better studies - but this is a good start.