Fermented foods: trendy but they’re not probiotics
Although clinical evidence for its role in health is limited, lab evidence is promising
FERMENTATION is a case of what’s old is new again – an ancient foodprocessing-method-turned hot trend, with companies churning out products incorporating kefir, kimchi, sauerkraut and kombucha that are promoted as being probiotics. But do they offer probiotic benefits?
The short answer is probably not. But that doesn’t mean the foods are without benefit.
First, let’s clear up what “probiotic” means. Scientists define probiotics as live microorganisms (microbes) which, when administered in adequate amounts, confer a health benefit.
Probiotics can contribute to digestive and immune system health and crowd out harmful microbes in the gut (large intestine).
They also create some nutrients, including vitamin K and many of the B vitamins, and help our bodies absorb other nutrients.
However, most fermented foods do not meet the criteria, and would not give you the same benefit as a probiotic supplement might.
Robert Hutkins, a food science professor and researcher at the University of Nebraska at Lincoln and author of Microbiology and Technology of Fermented Foods, said that most microbes, which include fungi as well as bacteria, in fermented foods have not been characterised or defined, let alone tested in clinical trials to see if they offer probiotic health benefits.
This is partly due to logistics – the microbes in fermented foods vary by manufacturer, batch and location.
“We don’t know how many bacteria are helping us,” said Cynthia Lair, a nutrition faculty member at Bastyr University near Seattle, and author of Sourdough on the Rise: How to Confidently Make Whole Grain Sourdough Breads at Home.
“We haven’t even identified them all, so they haven’t all been studied.”
And then there’s the issue of how many live microbes might be needed to confer any benefit.
Some fermented foods, including fresh kimchi, sauerkraut and sour pickles, as well as yoghurt, kefir and kombucha, can contain 1 million to 1 trillion live microbes a gram. With other foods, the microbes are killed by baking, pasteurisation or filtering.
These include tempeh, most soy sauces, beer and wine, as well as any shelf-stable fermented foods. Aged cheeses retain few live microbes. It was long thought that baking killed all the microbes in fermented breads.
That is not the case, as Lair discovered when she created a new sourdough starter from a piece of one of her home-baked loaves.
A review published in August in the journal Nutrients found that clinical evidence for the role of fermented foods in digestive health and disease is limited, although laboratory evidence is promising.
The health effects of kefir, a fermented dairy beverage, are the best studied, but the rest of the fermented food world is more of a question mark. If they’re not “probiotic”, what do fermented foods do for you? Plenty, as it turns out. Fermentation helps preserve food by suppressing microbes that might make us sick – something humans figured out early on.
“Properly made cheese and sausages would have lasted for months or years, providing a stable source of protein, minerals and vitamins for when food resources were scarce,” Hutkins said.
“Even today, fermented foods serve as an excellent source of these nutrients.”
He points to cheese and yoghurt, which are among the best sources of calcium in the human diet, as well as fermented vegetables such as kimchi and sauerkraut, which contain B vitamins and vitamin C.
Hutkins said that even when there are no live microbes left in the finished food, the dead microbes might enhance the food’s nutritional value.