*IMPORTANT* As the field grows basic concepts need to be highlighted. Validated placebos, in any probiotic study in the literature, for any organism, are the absence of living cells. Heat-killed cells will be, indeed, a simple source of carbon, i.e., another treatment (1/3)

Not a good control! This is how researchers have been testing probiotics for decades (e.g. non-fermented milk as a control to probiotics for humans; no cells to test plant probiotics; no cells in aquaculture, no cells for frogs, etc. Good tools to validate probiotics could be(2/3

for example, the successful incorporation of probiotics, microbial shifts, or microscopy. There is no way that "eaten bacteria" will be significantly enriched as members of the host microbiome if they are not probiotics, so check their stability and beneficial effect (3/3).

And for those who still say that probiotics are "only" a good source of carbon, well not any food promote health, but only prebiotics, and they are hard to find and equally awesome ;-) (4/4) @reefgenomics @DiseaseMatters @ute_hentschel @phylogenomics @PolypProtectors @VibrioSoup

If we feed them with killed cells and probiotics are incorporated (not eaten), we are comparing probiotics x food, two distinct treatments. We can develop even better controls in the future, as science moves forward, but killed cells are definitely not a good one, in my opinion.