How we write and cite
Every number has a source, and the source has a limitation
A figure on this site — a gram, a percentage, a number of kilograms — comes from a named source you can open, listed at the bottom of the page. Next to each source we record its limitation: what the study was, whom it studied, and what it therefore cannot tell you. The limitation is part of the citation, not a footnote. A source that does not say what we need is not cited for it; if no source exists, the page says "no established figure" instead of inventing one.
Which sources we use, in order
- Official expert reports and guidelines — WHO, FAO, EFSA, the National Academies, NICE, national ministries.
- Systematic reviews and meta-analyses — Cochrane and the major journals.
- Large randomised trials with hard outcomes.
- Observational cohorts, only for associations and always named as such.
- Mechanism and expert opinion, only as context, never as evidence.
No number in a structured field comes from below the third level.
The evidence grade on each page
- A — several systematic reviews or trials agree in one direction.
- B — systematic reviews with limitations: heterogeneity, short follow-up, high dropout.
- C — single trials or observational data.
- D — mechanism, opinion or marketing without clinical confirmation.
The grade applies to the page's central claim, and the page says which claim that is.
What we may reproduce and what we may only cite
Facts are free; wording is not. We paraphrase in our own words and give the number, the source, its limitation and a link. We do not copy paragraphs, redraw tables or translate figures. Some of our most important sources — WHO, EFSA, Cochrane, NICE — are published under licences that permit citation but not reproduction or translation, and the source list marks them "cited, not reproduced". Public-domain and CC BY sources may be quoted with attribution.
Review and correction
Every page shows the date it was last reviewed and the date its sources were last checked. Pages about ways of eating are re-checked at least every twelve months or when a guideline changes; a page whose sources are overdue says so at the top. When a source we cite is retracted, updated or reversed, the page changes and the change is recorded. When we are wrong, we say so on the page rather than editing quietly. Corrections and questions: see Contact.
How the text is made
Pages are written from the sources above, drafted and translated with the help of AI tools, and reviewed by a person before publication. The English text is the original; other languages are translations of a specific version of it, and a translation that has fallen behind says so.