Our nutrition methodology explains where food values come from and how the tools calculate their estimates. A useful number should come with a reproducible method. Here is the method used by the food reference and recipe library.
Nutrition methodology: exact records, visible preparation states
Our initial 75-food dataset comes from the official USDA FoodData Central SR Legacy CSV archive. It is historical reference data: the final April 2018 SR Legacy release, published in FoodData Central in 2019. Every entry preserves its FDC ID, NDB identifier, original nutrient row identifiers and documented food description. The records keep raw, cooked, drained and edible portions distinct.
USDA dataset downloads · Exact source archive · SR Legacy documentation. USDA data are public domain; no USDA endorsement is implied.
Scale once, sum before rounding
For each nutrient, multiply the source’s amount per 100 grams by the edible ingredient grams divided by 100. For a recipe, add the ingredient amounts, then divide by the stated servings. The tools retain full precision until they display values. We do not replace the USDA energy field with a calculated calorie estimate.
| Displayed count | Calculation | Interpretation |
|---|---|---|
| Protein blocks | Protein grams ÷ 7 | A nutrient count, not the food’s weight. |
| Carbohydrate blocks | max(total carbohydrate − fiber, 0) ÷ 9 | Available-carbohydrate convention. |
| Total-fat blocks | Total fat grams ÷ 3 | A separately labeled mixed-food/meal reference. |
| Original added-fat equivalent | Fat grams ÷ 1.5 | The legacy food tool’s convention; not interchangeable with total-fat blocks. |
The Zone publisher’s guide describes different fat conventions depending on the accompanying protein source. Our interface keeps the two displayed quantities distinct instead of pretending they always represent the same meal.
What is and is not verified
We compared source values against the USDA nutrient rows and checked recipe arithmetic independently. We have not analyzed individual recipes in a laboratory or physically kitchen-tested them. Times are editorial estimates. Ingredient substitutions, product differences, cooking losses and portion measurement can change actual nutrition.
The tools offer only household measures documented for that exact USDA record. They do not infer a generic cup-to-gram conversion or treat missing data as zero.
Calculator compatibility
The tools retain the original four autocomplete entries as legacy data, without relabeling them as USDA records. A new USDA selection fills protein, available carbohydrate and fat from its own documented entry. Original food-portion rounding remains 0.25 for carbohydrate, 0.5 for protein and 0.05 for fat in the selected unit.
The prescription calculator’s default unit-consistent mode converts kilograms to pounds before applying the original pound calculation and rounded stages. The visitor-facing calculator uses this standard estimate only. The calculator retains the old meal-allocation table with missing/mismatched-result notices; it does not invent a new meal distribution.
Inspect the food reference → · Explore recipes → · Read the evidence guide →