There’s a growing body of research that the best way to ensure a diverse microbiome is to eat many different plant foods each week. Recent research at the University of California San Diego suggests the magic number is 30:

https://www.humnutrition.com/blog/30-plants-per-week/

Every plant makes unique contributions to the microbiome because of the unique chemical composition of its prebiotic fiber. Every different type of nut, bean, or grain is considered a separate plant food. So, a week that includes whole-grain rye, wheat, rice, spelt, oats, black beans, garbanzo beans, pinto beans, lentils, almonds, walnuts, pumpkin seeds, sunflower seeds, pecans, and cacao get you half of the way there without even eating a single fruit or vegetable.

Here’s some useful guidelines about how to support a healthy microbiome from a research nutritionist and clinical dietitian (RD, PhD) who specializes in gut health:

https://www.theguthealthdoctor.com/all-articles/10-step-gut-makeover-plan-healthy-gut

Keep in mind that it is critical to get the naturally occurring diverse plant fibers. Juices or extracts with one or a few added fiber types will not give you the same benefit.

It’s admittedly very hard to reconcile the evidence that comes from epidemiological research on plant based diet in blue zones and basic science and clinical research on how to support a healthy microbiome with the recommendations of some rather extreme advocates of Paleo, Keto, and low-carb diets. Some researchers coming from the perspective of microbiomics note that many of the foods that modern Americans have adverse reactions to because of excessive intestinal permeability may actually be caused by microbiome issues that were established very early in life and even during gestation.