The answer is… not necessarily. If fermented foods were a relationship category they’d read ‘it’s complicated’.
Fermentation is a traditional method of preserving food that also happens to produce lots of tasty flavours. It happens when harmless; naturally occurring live bacteria consume sugars in foods (like vegetables and milk) and produce probiotic bacteria + various gases. As well as a slightly sour, tangy taste, this prevents harmful bacteria from growing.
Although fermented foods are made with live microbes, many commercial products are baked or pasteurised (heat-treated) to extend shelf life, which can kill off the live cultures. So, just because a food is fermented, it doesn’t mean it contains live microbes. An example is sourdough bread, where the bacteria produced are inactivated by heat, or pasteurised sauerkraut. As for aged cheeses, most live bacteria die during storage.
THE MEANING OF PROBIOTIC
Scientifically speaking, in order for something to be ‘probiotic’, it has to meet three criteria - it has to deliver live bacteria in sufficient enough quantities to deliver a health benefit. And for this reason, many products can't really be called probiotic.
Some fermented food products contain live microbes, but they are not at the level where they can be ‘probiotic’. In a recent review, researchers found fermented dairy foods consistently contained higher levels, but there was a wide variation depending on product age and region.
This means there’s more chance that fermented foods made at home or in small batches contain higher levels of live helpful microbes. This doesn’t mean commercially produced fermented foods aren’t of any benefit – compounds produced by the microbes when they were live may have positive effects - and if you're eating a fermented vegetable you also stand to benefit from the fibre, vitamins and minerals.
The problem is we don’t yet know enough about the effects of fermented foods to be sure – human trials are thin on the ground but I hope we’ll see more in the coming years.