Such Sweet Things Out of Such Corruptions

The Season

September is harvest and the start of fermentation: cabbage into kraut, apples into cider, grapes into wine, fallen leaves into next year's soil. As the last hallmark and the close of the series, dysbiosis returns everything to the ground the other eleven grew from. The year ends at the gardener's question, as Candide does: what are you going to cultivate now?

The Biology

The gut holds a living community of trillions of microbes that ferment the fibre we cannot digest into small fatty acids. Those feed the cells of the colon, keep the gut wall sealed, and calm the immune system. With age, and especially with frailty, a narrow diet, antibiotics and inactivity, that community tends to thin out. Diversity falls, fibre-fermenting species fade, oxygen-tolerant opportunists spread, and the gut wall leaks more, feeding low-grade inflammation. López-Otín and colleagues named this "dysbiosis" the twelfth hallmark of aging in 2023. Healthy ageing does not mean keeping a young microbiome. In large cohorts, healthy older people's microbiomes keep changing and become more individual. What seems to matter is a community that stays alive, varied and fed.

Anchor facts

• Across more than 9,000 people, gut microbiomes grew more individual from mid-life, and older adults who kept a Bacteroides-dominated, low-uniqueness pattern had lower four-year survival (Wilmanski et al., Nat Metab 2021). Source ↗
• In a 17-week randomised trial, a diet high in fermented foods steadily raised microbiome diversity and lowered inflammatory markers, while a high-fibre diet did not raise diversity (Wastyk et al., Cell 2021). Source ↗
• After a 4-day broad-spectrum antibiotic course, healthy men's gut communities returned to near-baseline within about six weeks, but nine common species were still missing in most of them at six months (Palleja et al., Nat Microbiol 2018). Source ↗

The Canon

• Walt Whitman — "This Compost" (first published 1856 in Leaves of Grass as "Poem of Wonder at The Resurrection of The Wheat"; given its present title in 1881) — stanza 2. The speaker, afraid of the diseased dead buried in the soil, is overwhelmed that the same earth sends up clean wheat and fruit: "What chemistry!" / "It grows such sweet things out of such corruptions." That is fermentation as renewal, the microbiome's whole bargain.
• Virgil — Georgics (29 BC) — Book 1, lines 71–83 (fallow, crop rotation, and not being ashamed to feed exhausted fields with rich dung). The Roman farmer's manual treats fertility as something kept up by rotation, rest and feeding the soil, not by forcing it. Diversity of crops and the feeding of the soil map onto plant diversity and fibre.
• Voltaire — Candide (1759) — chapter 30, the closing line: "il faut cultiver notre jardin." After every grand theory fails, what is left is small daily tending. It fits the protocol's verdict that the evidence rests on ordinary habits (fibre, fermented food, movement, fewer unnecessary antibiotics) and not on products, and it closes the series as it closes the book.
• Genesis 2:8–15 (Hebrew Bible; King James Version, 1611) — verse 15. The man is put into the garden "to dress it and to keep it." Two verbs, cultivate and guard, match the two halves of the ledger: feed the community, and protect it from harm.
• Andrew Marvell — "The Garden" (published 1681) — stanza 6. The mind withdraws into the garden, "Annihilating all that's made / To a green thought in a green shade." It is a poem of attention, and it bridges to the contemplative practice: presence as a kind of inner cultivation.
• John Keats — "To Autumn" (1819) — stanza 1. "Season of mists and mellow fruitfulness" gives the ripeness that tips into decay. Stanza 2's figure drowsing by the cider-press is the season's fermentation in one image.