The Nutrition Dex is an editorial publication covering measurement accuracy in nutrition: USDA FoodData Central, nutrition-label methodology, kitchen-scale precision, validation against reference meals, and the error metrics — MAE, MAPE, RMSE — that distinguish a credible calorie figure from a guess.https://thenutritiondex.com/en-ushttps://thenutritiondex.com/glossary/usda-fooddata-central/https://thenutritiondex.com/glossary/usda-fooddata-central/The U.S. Department of Agriculture's integrated food-composition database, comprising five source datasets and serving as the reference ledger for most American nutrition labelling and research.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/sr-legacy/https://thenutritiondex.com/glossary/sr-legacy/The frozen April 2018 final release of the USDA's Standard Reference database, preserved inside FoodData Central as the historical reference backbone for legacy research.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/foundation-foods/https://thenutritiondex.com/glossary/foundation-foods/The USDA's current-generation analytical food-composition dataset, distinguished by documented sampling protocols, nutrient uncertainty estimates, and sample provenance metadata.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/fndds/https://thenutritiondex.com/glossary/fndds/The USDA Agricultural Research Service's dietary-recall reference database, tied to What We Eat in America and NHANES, and the canonical source for 24-hour recall coding in U.S. nutritional epidemiology.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/usda-branded-foods-database/https://thenutritiondex.com/glossary/usda-branded-foods-database/The manufacturer-submitted portion of FoodData Central, containing roughly 1.5 million packaged-food entries with label-derived nutrient values and variable update timeliness.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/atwater-factors/https://thenutritiondex.com/glossary/atwater-factors/The 4-9-4 kilocalorie-per-gram coefficients (protein, fat, carbohydrate) derived from Wilbur Atwater's late-19th-century calorimetry work and still used to compute food energy on most nutrition labels.Sun, 19 Apr 2026 00:00:00 GMTbiochemistryJames Oliverhttps://thenutritiondex.com/glossary/bomb-calorimetry/https://thenutritiondex.com/glossary/bomb-calorimetry/The laboratory method for measuring a food's total energy content by igniting a dried sample inside an oxygen-pressurised steel vessel and recording the heat released into a surrounding water jacket.Sun, 19 Apr 2026 00:00:00 GMTbiochemistryJames Oliverhttps://thenutritiondex.com/glossary/atwater-specific-factors/https://thenutritiondex.com/glossary/atwater-specific-factors/A refined set of Atwater coefficients that vary by food category to account for digestibility differences — used by some USDA database entries and accepted by regulators as an alternative to the general 4-9-4 system.Sun, 19 Apr 2026 00:00:00 GMTbiochemistryJames Oliverhttps://thenutritiondex.com/glossary/nutrition-facts-label/https://thenutritiondex.com/glossary/nutrition-facts-label/The FDA-regulated nutrition disclosure panel required on most U.S. packaged foods, governed by 21 CFR 101.9 and last materially revised in 2016 with a 2020 compliance deadline.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/fda-serving-size/https://thenutritiondex.com/glossary/fda-serving-size/The per-serving reference quantity required on a Nutrition Facts panel, determined by the FDA's Reference Amounts Customarily Consumed (RACC) table rather than set freely by the manufacturer.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/racc/https://thenutritiondex.com/glossary/racc/The FDA regulatory table in 21 CFR 101.12 that assigns a reference serving amount to each of approximately 140 food categories, based on national consumption survey data.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/daily-value/https://thenutritiondex.com/glossary/daily-value/The FDA reference intake figures used to contextualise nutrient content on Nutrition Facts labels — derived partly from the National Academies' Dietary Reference Intakes and partly from older regulatory constructs.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/percent-dv/https://thenutritiondex.com/glossary/percent-dv/The ratio of a nutrient amount in a serving to the FDA Daily Value, expressed as a percentage on a Nutrition Facts panel to give consumers a quick gauge of whether an amount is low or high.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/dual-column-labeling/https://thenutritiondex.com/glossary/dual-column-labeling/The FDA-required two-column nutrition panel format used on packages containing 200 to 300 per cent of a single Reference Amount, showing both per-serving and per-container nutrient figures.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/label-rounding-rules/https://thenutritiondex.com/glossary/label-rounding-rules/The FDA-specified rules for rounding nutrient quantities on Nutrition Facts labels — increments that differ by nutrient and magnitude and that introduce an irreducible precision floor into any label-derived tracking.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/twenty-percent-tolerance-fda/https://thenutritiondex.com/glossary/twenty-percent-tolerance-fda/The FDA tolerance band in 21 CFR 101.9(g) permitting the analytically measured content of naturally-occurring nutrients to exceed the declared label value by up to 20 per cent without the product being deemed misbranded.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/mean-absolute-error/https://thenutritiondex.com/glossary/mean-absolute-error/The average of the absolute differences between estimated and reference values across a set of observations — the preferred first-line accuracy measure for calorie and nutrient estimation because its units match the thing being measured.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/mean-absolute-percentage-error/https://thenutritiondex.com/glossary/mean-absolute-percentage-error/The average of the absolute percentage differences between estimates and reference values — the accuracy measure most often quoted for consumer calorie-tracking apps because it scales cleanly across meals of different sizes.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/root-mean-square-error/https://thenutritiondex.com/glossary/root-mean-square-error/The square root of the mean of squared differences between estimates and reference values — an accuracy measure in the same units as the original quantity but one that weights large errors more heavily than MAE.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/accuracy-vs-precision/https://thenutritiondex.com/glossary/accuracy-vs-precision/Two distinct properties of a measurement system — accuracy is closeness to the true value, precision is the repeatability of measurements regardless of correctness — that consumer nutrition discourse routinely conflates.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/systematic-error-vs-random-error/https://thenutritiondex.com/glossary/systematic-error-vs-random-error/Systematic error is a consistent bias that shifts all measurements in a single direction; random error is the scatter of measurements around a central value. The two require different corrections.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/test-retest-reliability/https://thenutritiondex.com/glossary/test-retest-reliability/The degree to which a measurement method produces the same result on repeated application to the same underlying reality — the statistical core of what consumers mean when they ask whether a scale, app, or survey is "consistent."Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/inter-app-variance/https://thenutritiondex.com/glossary/inter-app-variance/The spread of calorie and nutrient estimates produced by different tracking apps for the same food or meal — a practical consequence of differing underlying databases, serving assumptions, and calculation choices.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/per-meal-error-band/https://thenutritiondex.com/glossary/per-meal-error-band/The expected range of estimation error for a single meal logged by a given method — the practical accuracy figure that matters for per-meal decisions, as distinct from daily or long-run averages.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/portion-size-error/https://thenutritiondex.com/glossary/portion-size-error/The contribution to total estimation error that arises from inaccurate determination of the amount of food consumed — often the dominant error source even when the nutrient database is correct.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/ingredient-visibility-error/https://thenutritiondex.com/glossary/ingredient-visibility-error/The estimation error introduced when ingredients are hidden from view (dressings, sauces, cooking fats, buried components) and therefore cannot be identified or quantified by a visual or photo-based method.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/mixed-dish-error/https://thenutritiondex.com/glossary/mixed-dish-error/The elevated estimation error specific to composite meals — casseroles, stews, stir-fries, curries, salads — whose ingredient composition cannot be fully inferred from appearance.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/low-light-photo-error/https://thenutritiondex.com/glossary/low-light-photo-error/The degradation in photo-based food-identification and portion-estimation accuracy that occurs when images are captured in poor lighting — restaurant interiors, evening meals, dim kitchens.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/small-portion-error/https://thenutritiondex.com/glossary/small-portion-error/The relatively elevated percentage error that affects small portions — where a fixed absolute error (in grams or kilocalories) represents a larger fraction of the true value.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/validated-photo-database/https://thenutritiondex.com/glossary/validated-photo-database/A curated corpus of food images paired with laboratory-measured nutrient reference values — the ground-truth resource against which photo-based estimation methods are benchmarked.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/laboratory-weighed-reference-meals/https://thenutritiondex.com/glossary/laboratory-weighed-reference-meals/Meals prepared and weighed ingredient-by-ingredient under controlled conditions, then analysed or calorimetrically measured, to serve as ground truth for validating dietary-assessment methods.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/kitchen-scale-precision/https://thenutritiondex.com/glossary/kitchen-scale-precision/The specification that determines how finely a kitchen scale can discriminate weights — 0.1g, 1g, or 2g are the three common tiers — and the principal determinant of weight-based logging accuracy.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/one-tenth-gram-scale/https://thenutritiondex.com/glossary/one-tenth-gram-scale/A kitchen or laboratory scale specified to display weight in 0.1-gram increments — the precision tier required for accurate logging of small-portion ingredients.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/one-gram-scale/https://thenutritiondex.com/glossary/one-gram-scale/A kitchen scale displaying weight in 1-gram increments — the workhorse precision tier for meal-scale weighing, typical capacity 3 to 5 kilograms.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/measuring-cup-vs-weight/https://thenutritiondex.com/glossary/measuring-cup-vs-weight/The accuracy gap between volume-based measurement (cups, tablespoons) and weight-based measurement (grams) — a gap driven by density variability, packing behaviour, and user reading error.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/density-based-conversion/https://thenutritiondex.com/glossary/density-based-conversion/The calculation that turns a volume measurement into a mass measurement by multiplying volume by the food's density — the source of most volume-to-weight error when a single density figure is used for a variable real-world food.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/liquid-volume-conversion/https://thenutritiondex.com/glossary/liquid-volume-conversion/The conversion between liquid volume units (millilitres, fluid ounces, cups) and mass (grams), with the wrinkle that U.S. and U.K. fluid ounces are different sizes.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/raw-vs-cooked-weight/https://thenutritiondex.com/glossary/raw-vs-cooked-weight/The gap between a food's weight before and after cooking, driven primarily by moisture loss and fat rendering — a source of systematic error when a database assumes one state and the user logs the other.Sun, 19 Apr 2026 00:00:00 GMTdietary-assessmentJames Oliverhttps://thenutritiondex.com/glossary/moisture-loss-in-cooking/https://thenutritiondex.com/glossary/moisture-loss-in-cooking/The reduction in a food's mass during cooking due to evaporation of water — the primary driver of the raw-to-cooked weight change and the main reason cooked-state databases exist.Sun, 19 Apr 2026 00:00:00 GMTbiochemistryJames Oliverhttps://thenutritiondex.com/glossary/fat-rendering/https://thenutritiondex.com/glossary/fat-rendering/The melting and separation of solid fat from meat during cooking — a component of cooking mass loss whose fate (discarded, retained, partially absorbed by other ingredients) determines whether the calories leave the meal or not.Sun, 19 Apr 2026 00:00:00 GMTbiochemistryJames Oliver