How we rate evidence

The principle

The Balance of Health exists so that someone who disagrees with us can inspect the same evidence we used and understand exactly how we reached a conclusion. That means showing sources, saying how strong the evidence is, presenting the strongest counterargument, and being explicit about what is uncertain.

If the evidence is inconvenient for a plant-based diet, we show it anyway.

How evidence is structured

Every important statement on the site passes through the same chain, and each link is a record you can open:

Claim: a single, quotable statement.
Short answer: the claim in plain English.
Key statistic: one number, with its unit, geography, year and source.
Explanation and chart: why the number is what it is.
Evidence strength: a rating and, always, the reason for it.
Source records: what each source found, its limitations, funding, and which claims it supports or challenges.
Original research: a direct link to the paper, report or dataset.
Methodology and limitations: how the numbers were produced and what they leave out.
Last reviewed: when a person last checked the record.

How we rate evidence strength

We use four levels. The rating describes the evidence for the claim as stated, not how much we like the conclusion. A claim can be rated strong and still have large uncertainties in its exact size.

Strong evidence: Supported by multiple systematic reviews or large, consistent studies using different methods, with few plausible alternative explanations.
Moderate evidence: Supported by good-quality studies that point the same way, but with gaps: fewer studies, mostly observational data, or some inconsistency.
Limited evidence: Some relevant studies exist but they are small, indirect, short-term or conflicting. The direction is plausible; the size of the effect is not settled.
Uncertain: The evidence is too thin, too mixed or too dependent on assumptions to support a confident conclusion either way.

Special care with health evidence

Most nutrition evidence comes from observing large groups over time. That can show associations but struggles to prove cause, because people who eat differently also live differently. We say when a finding is observational, when trials exist, and what the trials measured.

We report relative risks alongside a sense of absolute risk, because a 25% reduction of a small risk is a small number. We do not treat a vegan diet and a whole-food plant-based diet as the same thing.

Special care with environmental evidence

Environmental footprints come from life-cycle assessments, which depend on system boundaries and allocation choices. We report averages with ranges where the source gives them, compare foods on a nutritionally sensible basis, and note where methods (for example, how methane is counted) change the numbers.

We do not treat all plant foods as environmentally equivalent, nor all animal farming.

Countries, production systems and personalisation

Every statistic and food figure carries a geography. When you choose a country, we use its figures where a source provides them and fall back to global averages otherwise, always saying which. Country records also summarise local dietary guidance, fortification practice, welfare law and water stress, each with its own source.

Some foods have figures for several production systems (beef from dairy herds, grass-fed, feedlot; free-range and indoor chicken). The comparison tool shows the all-systems average by default and lets you choose a system; the source changes with it.

Telling us what you are mainly interested in reorders what comes first on a page. It never removes evidence. The preference and country are stored as cookies on your device; there are no accounts.

Counterarguments

For each major question we present the strongest opposing argument, as its proponents would state it. We then say what is correct about it, what the evidence supports, what may be misleading, and what remains uncertain. We do not construct straw men.

Source records

A citation on this site leads first to our record of the source, not straight off-site. The record summarises the study, its type, population and sample size, key findings, limitations, funding and conflicts, and an assessment of its quality. From there, one link takes you to the original.

Sources can support some claims and challenge others. We record both.

Sample data and the current state of the site

The site is being built ahead of its research database. Records marked 'Sample' are demonstration data: real publications, but with figures and summaries that have not yet been verified through our review process. They show how evidence will be presented. They should not be cited.

As verified research is imported, sample records will be replaced and the marker removed. Every record shows its status and last-reviewed date.

Review, corrections and funding

Each record carries a last-reviewed date and, where available, a reviewer. Our editorial policy, correction policy, reviewer policy and funding disclosure are being drafted and will be published here. Until then: we will correct errors promptly and note the correction on the page.