21 August 2026

How every number in these books is computed

Most cookbooks that print calorie counts do not say where they came from. Usually the answer is a nutrition app, which is a database of user-submitted entries of wildly varying quality, or another cookbook, which got it from an app.

Here is the method used for every figure in this series, in full, so you can check any of it.

Two databases, downloaded not queried

The primary source is USDA FoodData Central, SR Legacy release, which carries 7,793 generic unbranded foods and is public domain. The second is McCance and Widdowson Composition of Foods Integrated Dataset 2021, published by Public Health England under the Open Government Licence, which carries 2,886 foods.

Both are downloaded in bulk rather than queried live, so no figure in a printed book depends on an API that might rate-limit, change, or disappear.

When each one is used

USDA is primary. CoFID is used where the British product genuinely differs from the American one, which is not a preference but an accuracy problem. USDA bacon is 393 kcal per 100g. British streaky bacon is 276. Using the American figure would overstate every saving in every recipe that touches it.

The same applies to sausages, which carry rusk here; to cream, where the British fat grades are legally defined and differ; and to self-raising flour, which has no clean USDA equivalent.

The arithmetic

Each ingredient is matched to one database row, multiplied by its weight in grams, and the total divided by the number of servings. The traditional version is costed the same way from its own ingredient list, which is why the saving printed with each recipe is a measurement rather than a claim.

Salt is given as salt equivalent: sodium multiplied by 2.5 and divided by 1,000, the conversion used on British food labels. Salt added to pasta water is not counted, because most of it goes down the sink.

What gets printed

The appendix at the back of each book lists every ingredient, the database it came from, the reference number, and the exact row name. If you doubt a figure, that table tells you where to go and check it.

Where the closest available row is not exactly the thing in the recipe, the book says so. There is no ricotta salata in either database, so Pecorino Romano stands in, and the appendix prints that rather than hiding it in a footnote.

A number that could not be traced did not go in the book.

The swap kit is free, and it is the part of the book you would use most.