Gut Reset

the nerdy bit

In a Stanford study, 36 healthy adults were randomly put on a high-fibre or a high-fermented-food diet, 18 on each (Wastyk et al., 2021). Over the 10-week diet, the fermented-food group's gut bacteria grew steadily more diverse, and 19 of the 93 inflammatory proteins measured in their blood went down. They built up from less than one serving a day of foods like yogurt, kefir, kimchi and kombucha to about six, and the study tracked gut and blood, not skin.

For skin: in a 4-week Japanese trial, 40 women drank a probiotic fermented milk or plain milk every day, and skin hydration fell with plain milk but held steady with the fermented drink (Kano et al., 2013). In a 12-week trial of people aged 12 to 30, 42.5% of those taking a probiotic capsule improved, against 20.6% on a placebo, though that was a capsule, not food (Eguren et al., 2024). The limits: a 2022 review of 14 studies of fermented foods or lactic acid bacteria, with 884 people, found no overall gain in skin water content (Sun et al., 2022), and we found no trial of a fermented food on its own for breakouts.