Rice vinegar is just rice that has been fermented into vinegar. Although our paleolithic ancestors probably weren’t fermenting their food, much less grains, we can still incorporate a little rice vinegar into our diets.
The Benefits of Fermentation
To start with, the fermentation process is known to destroy anti-nutrients, so by fermenting rice, you eliminate much of the reason to avoid consuming grains. Fermented foods also have demonstrated health benefits in their own right, and vinegar is no different. Studies have shown vinegar can help improve insulin sensitivity and lower blood sugar.
Paleo and Carbohydrates
The other reason to avoid grains is they tend to be very high in carbohydrates, but by distilling them into vinegar, we remove that objection as well.
Mark Sisson addressed the pros and cons of vinegar.