The Gut Health Cookbook
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Fabulous ferments.

People have fermented food for thousands of years. Here is what fermented foods are, what the research says, and how to start.

By Michael Vestri, author of The Gut Health Cookbook. General information, not medical advice.

What counts as a fermented food?

An international panel of scientists defines fermented foods as foods made through the desired growth of microbes and the changes they make to the food.1 Yoghurt, kefir, sauerkraut, kimchi, miso, tempeh, kombucha, sourdough bread and many cheeses all qualify.

Not every fermented food still contains live microbes when you eat it. Baking sourdough, pasteurising sauerkraut or heat-treating yoghurt kills them. For live microbes, look for words such as "live", "raw" or "unpasteurised", and keep them in the fridge.

What does the research say?

In a 10-week trial at Stanford University, 36 healthy adults ate either a diet high in fermented foods or a diet high in fibre. The fermented foods group, averaging around six servings a day by the end, saw their gut microbiome diversity increase and a range of inflammation markers fall.2 It was a small study, and more research is needed, but it was a striking result.

The scientific panel is optimistic but careful: much of the evidence so far comes from population studies rather than controlled trials, and most studies have focused on a few types of fermented food, such as yoghurt.1

How to begin

  • Start small. A spoonful of sauerkraut or kimchi, or a small glass of kefir, then build up over a few weeks.
  • Make it part of a meal. Kraut on the side of eggs, kefir in a smoothie, miso stirred into soup or a dressing.
  • Mix them up. Different ferments bring different microbes.
  • Try making your own. Sauerkraut needs only cabbage, salt and a jar. The book includes four simple ferments to make at home.

Safety first: use clean equipment, follow a tested recipe, and throw away anything that smells or looks wrong. If you are pregnant, have a weakened immune system or a medical condition, check with a healthcare professional before eating unpasteurised foods.

Sources

  1. Marco ML et al. The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on fermented foods. Nature Reviews Gastroenterology & Hepatology, 2021. doi.org/10.1038/s41575-020-00390-5
  2. Wastyk HC et al. Gut-microbiota-targeted diets modulate human immune status. Cell, 2021. doi.org/10.1016/j.cell.2021.06.019
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