Tim Spector’s guide to fermentation is meticulous and persuasive

Ferment
Tim Spector (Jonathan Cape (UK); US TBC)

There are two reasons why humans became interested in fermentation: preservation and pleasure. Before refrigeration, the process let us store drinks like mead for months when water could be deadly. And milk that spoiled within a day could last for weeks as yogurt or cheese. We grew to enjoy these tangy flavours, and the microbes that created such delicacies not only produced the odd impromptu aperitif, but also brought many health benefits.

Today, fermented foods like kimchi and sauerkraut are firmly on trend. Yet, as doctor and geneticist Tim Spector argues in his new book Ferment: The life-changing power of microbes, this isn’t really something new – we evolved to consume such produce as a regular part of our diet.

He begins with the basics: fermentation is simply the transformation of food by microbes. The effects of this aren’t at all simple, however, with consequences not just for the flavour and longevity of food, but also our health. Even dead microbes can influence our body and brain.

Fermentation and our microbiome are intimately linked. Fermented products give gut microbes raw materials to turn into nutrients and active molecules, such as short-chain fatty acids, which help regulate the immune system, writes Spector. These foods also assist microbes in maintaining the gut’s mucus barrier, preventing inflammation.

They are probiotics, too, adding millions of microbes to our guts. A diverse microbiome, explains Spector, has been linked to better health in a wide range of studies. Improving this diversity by eating fermented foods might even play a role in how well cancer treatments work, he writes.

The most compelling parts of Ferment explore this “microbial pharmacy”, demonstrating how, if only in small studies so far, fermented products are linked to improvements in everything from irritable bowel syndrome to anxiety and immune health.

Spector’s own research suggests people who regularly ate fermented foods had around 14 per cent less severe covid-19 symptoms compared with those taking other supplements, such as vitamin C. As with many nutrition studies, it is hard to distinguish correlation from causation, but Spector draws on multiple strands of evidence to build a persuasive case for eating fermented food.

The book is peppered with interesting facts. For instance, did you know that scientists have been unable to reproduce natural kefir grain (the “starter” for any good kefir) in the lab, despite their attempts to introduce the 30 or so microbes it contains to each other?

Throughout Ferment, we are reminded of how vital microbes are to us, and that we are only just scratching the surface of how we interact with them. Spector’s access to health data often allows him to fill in gaps where other studies fall short, and although his company’s gut supplements are mentioned, he avoids straying into marketing territory.

At its best, the book balances science, medical anecdotes and Spector’s own fermentation journey with practical advice. In those moments, the writing feels authentic and useful, especially when guiding readers on what foods to choose – pick kefir made from grains in whole milk, for example, as these contain yeasts as well as multiple microbes, which are likely to have greater health benefits.

At times, though, Ferment is a little repetitive, with knowledge occasionally prioritised over narrative. And despite Spector warning against overinterpreting animal studies, the infancy of the field means he is often forced to lean heavily on them himself. Still, this is a persuasive, meticulously researched book. Its final chapters were particularly intriguing, looking ahead to a future that may include personalised microbes – a yogurt for depression, say, or a cheese that helps with menopause.

Once hesitant to ferment at home, I was persuaded to begin experimenting by around page 40. By the end of the book, I had jars of kombucha and sauerkraut brewing in my pantry, an organic kefir grain winging its way to me and a fresh appreciation for the microbes – living and dead – that are shaping my health.

Helen Thomson is a writer based in London

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