I've learned a lot about prebiotics from the Paleobiotics site. In fact, he also wrote a book about the subject, which I've recently ordered. Overall, his research shows that prebiotic fibers were an essential component of the Paleo diet.
The next question is: did humans in the Paleolithc consume anything equivalent to modern probiotics in their diet? Probiotics generally come from two species: lactobacteria and bifidobacteria. The lactobacteria comes from the lactic acid in fermented foods. Bifidobacteria is mainly found in breast milk, though I've seen some claims that it is naturally found in some foods. Putting aside the issue of bifidobacteria, did Paleolithic man consume lactic acid bacteria via fermented foods?
In the Paleo Diet by Loren Cordain, fermented foods are prohibited. It would also seem that hunter-gatherers might consume fermented food only if they had to, so it would have probably been a backup source of calories - not a main one. I realize that fermented foods have been around thousands of years. I also know that some African cultures have certain fermented foods in their diet, but these cultures are relatively stationary. This doesn't exactly translate to what a mobile group of Paleolithic hunter-gatherers would consume.
Instead, it is likely that the prebiotics consumed in Paleolithic diets fed the probiotic bacteria in their guts. Prebiotics are undigestible fibers that are consumed by probiotic bacteria. Without prebiotics, you would need a steady supply of probiotics (fermented food) to keep up the levels of good bacteria in the gut.
Also, it appears that prebiotics are actually more effective at increasing good bacteria in the gut than probiotics. This study compared prebiotics versus probiotics in men. The men who took prebiotics increased their good gut bacteria by a massive amount, while the group taking probiotics saw little change.
In addition, modern probiotics tend to contain just one or a few strands of good bacteria. This approach of increasing only certain strands of lactobacteria or bifidobacteria may not be the most natural approach. A person might be better off consuming a large amount of prebiotic fiber, which would then fuel the growth of many different strands of good bacteria in the gut.
