Glossary
Fiber
Carbohydrate human enzymes cannot break down, left for colon bacteria to ferment into short-chain fatty acids. American adults average about 17 g a day; pooled benefits peaked at 25 to 29 g.
Published Updated
Graded claims that mention Fiber
- Can a greens powder replace vegetables?Expensive vitamins, and no substitute for vegetables.Evidence grade: Emerging. Early, small, animal-only, or actively contested.
Chapters of the book that mention Fiber
Where this comes from
In the reference topic that owns this term
Reference topic 12, The Gut That Expects Dirt, states the mismatch as a card: what the system evolved to expect, what it gets instead, and what happens in the gap.
Mismatch card
- What it expects
Tens of grams of fiber a day from many plants, a seasonal menu, and microbes from soil and food.
- What it gets
About 17 g of fiber a day (the US adult average), a narrow and refined diet, courses of antibiotics, and sanitized surroundings.
- What happens in the gap
Fewer species and less fermentation, with links to disease still being untangled.
What that chapter recommends
3 of the 7 graded recommendations in Reference topic 12, strongest evidence first. How the grades work.
Eat more fiber, from more kinds of plant
StrongEvidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.Aim for at least 25 g a day. In meta-analyses the benefit was greatest at 25-29 g, and more may help. The US adult average is about 17 g.
Add fermented foods with live cultures
ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.Trial participants worked up over four weeks to about six servings a day; start with one. Yogurt, kefir, most cheeses, miso and unheated fermented vegetables can carry live microbes; bread, vinegar pickles and...
Skip the probiotic aisle
ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.unless a clinician recommends one for a specific reason.
Related terms
Graded recommendations elsewhere that mention Fiber
- Aim for at least 25 g of fiber a dayEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.Topic 13
- Skip raw milk, worms and immune-training supplementsEvidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.Topic 18
Other reference topics that mention Fiber
The argument behind this term, its studies and its notes are in Reference topic 12 of the reference library. The book gives the practical version. Get the book.