I take probiotics in food form (water kefir, home-made yogurt.)

You have to define healthy. It's a little hard to believe that there are many people who have totally healthy gut flora in today's environment and that includes those of us taking probiotics. Everything's against us because we live in an artificial environment which is both "too sterile" and toxic and we eat food that is widely considered inferior compared to even 50 years ago.

Now, if you define healthy as symptom free that creates a reasonable group but I haven't known that many people who always feel high energy, cheerful, well rested, etc.

The nice thing about probiotics is, if you happen to have a healthy community of gut flora the probiotics aren't going to hurt you. Just as with overall nutrition, I believe the best choice is real foods vs. a pill or capsule. And home made is definitely better than any commercial product.

Because there is much more that we don't know about human biology than we do know, I think otherwise healthy should not take any supplements, except those for which a compelling argument can be made that such supplement is needed to return the person to a more "paleo" state. For example, vitamin D is lacking in our modern lives for people that spend all day working inside. Another argument might be made for certain minerals potentially lacking in our food because of soil depletion or geography. With respect to probiotics, humans used to eat more fermented foods prior to the advent of refrigeration. That said, fermented and preserved foods are a neolithic thing, more than a paleo thing, in that they helped stretch the fall harvest (think: agriculture) through the winter. Paleolithic tribes were probably less likely, or even unlikely, to eat such foods. Moreover, to the extent this is the argument, why not just eat fermented foods and not take probiotics?

One additional negative with many commercially available probiotics is that they come in phthalate "enteric" coatings. Although there is currently no evidence that the specific type of phthalate used causes birth defects or other problems, there is not much evidence that they don't either. And, generally, there is not a whole lot of difference between the chemical structure of one phthalate as compared to another... I try to avoid them wherever possible.

My personal experience with probiotics is limited. They helped me once with a minor but chronic sore throat (had it for months). I broke open a New Chapter (non-enteric) probiotic, mixed it with water, and gargled... The sore throat disappeared within half an hour of the first and only treatment and did not return again... I thought that was compelling evidence... Aside from this one positive experience, however, the only thing I have ever noticed from actually swallowing probiotics (and I've tried a few brands, including ones that sport enteric coatings) is bloating and gas. I do not now take them.

From everything I've read probiotics help some people, don't help others, and some people can't tolerate them at all such as myself. What's just as important as the source of bacteria is your source of food for all your bacteria. Fecal transplants are so effective because they provide the patient with anaerobic bacteria that can't survive in the presence of oxygen and therefore can't be put in a probiotic. If you're healthy and eating a paleo diet you don't need probiotics, especially if you're having fermented foods and drinks.

I don't see any reason for anyone to NOT eat sauerkraut. :)

My common sense test says they are neither harming nor helping a healthy individual. Our guts are full of multiple species of bacteria, all in competition for the available nutrients. Bacteria multiply extremely quickly, so they will achieve a level of balance depending on your diet (a high fat diet will probably result in a different "mix" of species than a high carb diet.

Probiotics may be useful if you have just made a major change to your diet and want to jump start the bacteria. But multiple doses shouldn't be necessary. Likewise after antibiotics have been taken and have disrupted your gut bacteria.

The anecdotes I have read around fecal transplants support this somewhat. It appears that multiple treatments are not ordinarily required. Once introduced, the bacteria will flourish if nutrients are there.

I recently started Bio-Kult probiotics with the hope that it will help my asthma condition. Since going Paleo, my allergies have improved markedly, but I still have exercise and weather induced asthma. I've recently read some research indicating that allergies and asthma, among other conditions, begin in the gut, so for me, it is worth a look-see.

I think probiotics are a sham. I have experimented extensively with different brands, and also with Kombucha and various yogurts (the ones with culture and milk as the only ingredients) and found the latter to be far more effective.

If possible try to get beneficial bacteria in your system through your diet by eating fermented foods, such as homemade kefir (milk or water), homemade sauerkraut (or kimchi), or drinking kombucha. Eating real food is usually better than taking supplements.

The book "Wild Fermentation: The Flavor, Nutrition, and Craft of Live-Culture Foods" by Sandor Katz has lots of good fermentation ideas.