The one food change with a trial behind it

“Food as medicine” is a phrase that usually means nothing. Occasionally there is a trial behind it. This is one of those times.

In 2021 a team at Stanford School of Medicine published a randomised study in Cell — Wastyk, Fragiadakis and colleagues, with Justin and Erica Sonnenburg and Christopher Gardner as senior authors. Thirty-six healthy adults were randomly assigned to one of two diets for ten weeks: one high in fermented foods, the other high in fibre.

The interesting part is that the researchers expected fibre to win.

What the fermented group ate

Ordinary things. Yoghurt, kefir, fermented cottage cheese, kimchi and other fermented vegetables, vegetable brine drinks, and kombucha. No supplements. No powder. Groceries.

What happened

Two results, and they point the same way.

The first: overall gut microbial diversity went up in the fermented-food group. Diversity is one of the more robust markers we have of a gut microbiome in good shape, and it is notoriously hard to shift with diet. The effect scaled with the dose — the more servings, the larger the change.

The second: four types of immune cell showed less activation after ten weeks, and the levels of nineteen inflammatory proteins fell. Among them was interleukin-6, which is one of the proteins repeatedly linked to chronic inflammatory conditions.

Diversity went up. Nineteen inflammatory proteins went down. In ten weeks, on groceries.

And the fibre arm

This is the part that keeps the study honest. The high-fibre diet did not produce the same increase in microbial diversity, and did not lower the inflammatory markers across the board. The authors were careful about it: fibre is not thereby proven useless, ten weeks is short, and thirty-six people is a small trial. It may be that a gut microbiome depleted by a modern diet lacks the microbes needed to break down the extra fibre in the first place.

So the finding is not “fibre is out”. The finding is that fermented food did something measurable, quickly, in a randomised design — which is more than almost any wellness food claim can say.

What we do in the kitchen

• Something fermented at every meal, in small amounts. A spoon of kraut next to lunch beats a jar once a fortnight.
• Live, not pasteurised. Shelf-stable supermarket sauerkraut is usually cooked. Look in the chilled cabinet, and look for bubbles.
• Both, not either. We did not stop eating fibre. The trial compared two diets; it did not tell anyone to abandon vegetables.
• Start smaller than you think. A large first serving is how people decide fermented food does not agree with them.

It is the cheapest intervention on this whole site, and it is the one with the best trial behind it. That ordering is worth noticing.