Squash champion Olivia Weaver eats kimchi before breakfast and drinks bone broth at night. A Stanford trial backs the fermented morning, raising microbiome diversity and cutting inflammation; the broth, though, is mostly comfort.
Kimchi is cabbage that has been left to spoil under supervision. Salted, packed with chili and garlic, and sealed in a jar until the wild bacteria already living on the leaves turn it sour, fizzing, and faintly alive, it belongs to one of the oldest tricks humans have for keeping food through a winter, a trick invented over and over across the world long before anyone could see a microbe. For most of that history it was survival food. In Olivia Weaver’s kitchen, it is the first thing she eats every morning, before the eggs, before the coffee, a spoonful taken the way someone else might take a vitamin.
“Lemon water, a 15-minute stroll in the sunlight,” the professional squash player told NewBeauty, walking through a day that opens on fermentation and closes, at night, on “tea or bone broth.” She has landed, without necessarily meaning to, right where the science on fermented food gets interesting, because one of those two bookends has a landmark study behind it and the other has a warm mug.
The study came out of Stanford in 2021, and it even startled the people who ran it. Researchers took thirty-six healthy adults and split them onto two diets for ten weeks: one loaded with fiber, the other loaded with fermented foods, the kimchi and kefir and kombucha and briny vegetables Weaver now eats by habit. The fermented group’s gut bacteria grew more diverse, and nineteen markers of inflammation in their blood dropped, including one tied to rheumatoid arthritis and type 2 diabetes. “This is a stunning finding,” Justin Sonnenburg, an associate professor of microbiology and immunology at Stanford, said in the university’s account of the research. “It provides one of the first examples of how a simple change in diet can reproducibly remodel the microbiota across a cohort of healthy adults.”
The strange part was the other group. Fiber is the thing nutritionists have spent a generation telling people to eat more of, and over ten weeks it moved almost nothing. “We expected high fiber to have a more universally beneficial effect,” said Erica Sonnenburg, a senior research scientist and co-author. “The data suggest that increased fiber intake alone over a short time period is insufficient to increase microbiota diversity.” The team was careful not to bury fiber on the strength of one trial, and a co-senior author, Stanford Prevention Research Center nutrition-studies director Christopher Gardner, called the work “a proof-of-concept study.” But the fermented result was immediate and hard to argue with.
What counts as a fermented food, and what doesn’t
The word fermented does a lot of hiding on grocery shelves, and Weaver’s plain kimchi is not the same as most things wearing the label. “Some products are initially fermented but then pasteurized afterwards, and although pasteurization extends the food storage life, unfortunately it also destroys the active cultures in the process,” Stephen Devries, a preventive cardiologist who runs the nonprofit Gaples Institute, told the American Medical Association. Vinegar pickles are out for the same reason. “The acidity in vinegar preserves the food, but vinegar doesn’t support the growth of the beneficial bacteria needed for fermentation,” Devries said. Even the real thing can be undercut by what is added to it, salt in the kimchi and miso, sugar in the kombucha and flavored yogurts. “The healthiest choices of yogurt and kefir are unsweetened,” Devries said. Weaver, eating hers straight, is doing the version the research actually rewards.
The bone broth she drinks at night has a softer verdict. “There’s no evidence that bone broth has greater health benefits than any other broths,” L.J. Amaral, a clinical dietitian at Cedars-Sinai, told Cedars-Sinai, before offering the reason people swear by it anyway. “There are studies that show how drinking warm liquids does have a positive effect on the body and how we feel,” she said. If the warmth is the active ingredient, tea or a vegetable broth delivers it just as well, and leaves the animal out of it. Amaral does not tell anyone to quit bone broth, and a warm cup after a hard day of training is a real comfort, just a different thing from a spoonful of live cabbage that turns up in the bloodwork ten weeks later.
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