Nutrition Reference is an editorially-independent glossary of nutrition science terminology — macronutrient biochemistry, micronutrient bioavailability, metabolic physiology, and the concepts behind modern dietary assessment. Each entry is peer-reviewed against primary sources.https://nutritionreference.org/en-ushttps://nutritionreference.org/glossary/doubly-labelled-water/https://nutritionreference.org/glossary/doubly-labelled-water/The reference method for measuring total energy expenditure in free-living humans, using the differential elimination of two stable isotopes over one to two weeks.Thu, 17 Sep 2026 00:00:00 GMTdietary-assessmentDr. Helena Weisshttps://nutritionreference.org/glossary/weighed-food-record/https://nutritionreference.org/glossary/weighed-food-record/A prospective dietary assessment method in which every item consumed is weighed and recorded at the time of eating, used as the per-meal reference in instrument validation.Thu, 17 Sep 2026 00:00:00 GMTdietary-assessmentDr. Helena Weisshttps://nutritionreference.org/glossary/twenty-four-hour-dietary-recall/https://nutritionreference.org/glossary/twenty-four-hour-dietary-recall/A retrospective interview method in which a trained interviewer elicits everything consumed in the previous twenty-four hours, using a structured multiple-pass protocol.Thu, 17 Sep 2026 00:00:00 GMTdietary-assessmentDr. Helena Weisshttps://nutritionreference.org/glossary/food-frequency-questionnaire/https://nutritionreference.org/glossary/food-frequency-questionnaire/A retrospective instrument that asks how often each of a fixed list of foods was consumed over months or a year, designed to rank individuals by habitual intake rather than to quantify it precisely.Thu, 17 Sep 2026 00:00:00 GMTdietary-assessmentDr. Helena Weisshttps://nutritionreference.org/glossary/amino-acids/https://nutritionreference.org/glossary/amino-acids/The organic building blocks that assemble into proteins and serve as precursors to neurotransmitters, hormones, and metabolic intermediates.Sun, 06 Sep 2026 00:00:00 GMTmacronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/essential-amino-acids/https://nutritionreference.org/glossary/essential-amino-acids/The nine amino acids the adult human body cannot synthesize de novo in adequate quantity and must obtain from dietary protein.Sun, 06 Sep 2026 00:00:00 GMTmacronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/leucine/https://nutritionreference.org/glossary/leucine/A branched-chain essential amino acid that serves as the principal nutritional trigger of muscle protein synthesis via mTORC1 signaling.Sun, 06 Sep 2026 00:00:00 GMTmacronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/bcaas/https://nutritionreference.org/glossary/bcaas/The three essential amino acids — leucine, isoleucine, and valine — whose aliphatic side chains share a common branched structure and degradation pathway.Sun, 06 Sep 2026 00:00:00 GMTmacronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/whey-protein/https://nutritionreference.org/glossary/whey-protein/The soluble protein fraction of milk, rich in essential amino acids and leucine, with rapid digestion kinetics that make it a reference protein in muscle metabolism research.Sun, 06 Sep 2026 00:00:00 GMTmacronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/casein-protein/https://nutritionreference.org/glossary/casein-protein/The insoluble phosphoprotein fraction of milk that forms slowly digested micellar curds in the stomach, producing prolonged postprandial amino acidemia.Sun, 06 Sep 2026 00:00:00 GMTmacronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/plant-protein/https://nutritionreference.org/glossary/plant-protein/Dietary protein derived from plant sources — legumes, grains, nuts, seeds — with amino acid profiles and digestibility characteristics distinct from animal proteins.Sun, 06 Sep 2026 00:00:00 GMTmacronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/diaas-score/https://nutritionreference.org/glossary/diaas-score/A protein quality metric that scores dietary protein by the ileal digestibility of each indispensable amino acid relative to human requirement, recommended by FAO in 2013 as successor to PDCAAS.Sun, 06 Sep 2026 00:00:00 GMTmacronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/pdcaas-score/https://nutritionreference.org/glossary/pdcaas-score/A protein quality metric introduced by FAO/WHO in 1989 that scores proteins by amino acid composition corrected for fecal digestibility, with values truncated at 1.00.Sun, 06 Sep 2026 00:00:00 GMTmacronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/protein-leverage-hypothesis/https://nutritionreference.org/glossary/protein-leverage-hypothesis/The hypothesis that humans prioritize absolute protein intake over total energy intake, overeating fats and carbohydrates until a protein quota is met.Sun, 06 Sep 2026 00:00:00 GMTmetabolic-physiologyDr. Helena Weisshttps://nutritionreference.org/glossary/muscle-protein-synthesis/https://nutritionreference.org/glossary/muscle-protein-synthesis/The anabolic process by which amino acids are assembled into new skeletal muscle proteins, driven by mTORC1 signaling and nutrient availability.Sun, 06 Sep 2026 00:00:00 GMTmetabolic-physiologyDr. Helena Weisshttps://nutritionreference.org/glossary/muscle-protein-breakdown/https://nutritionreference.org/glossary/muscle-protein-breakdown/The catabolic process by which skeletal muscle proteins are degraded to free amino acids via autophagy-lysosomal, ubiquitin-proteasome, and calpain systems.Sun, 06 Sep 2026 00:00:00 GMTmetabolic-physiologyDr. Helena Weisshttps://nutritionreference.org/glossary/net-protein-balance/https://nutritionreference.org/glossary/net-protein-balance/The algebraic difference between protein synthesis and protein breakdown, expressed per unit time and determining whether protein mass is accreted or lost.Sun, 06 Sep 2026 00:00:00 GMTmetabolic-physiologyDr. Helena Weisshttps://nutritionreference.org/glossary/gluconeogenesis/https://nutritionreference.org/glossary/gluconeogenesis/The metabolic pathway that synthesizes glucose from non-carbohydrate substrates — lactate, glycerol, and gluconeogenic amino acids — primarily in the liver and kidney.Sun, 06 Sep 2026 00:00:00 GMTmetabolic-physiologyDr. Helena Weisshttps://nutritionreference.org/glossary/ketogenesis/https://nutritionreference.org/glossary/ketogenesis/The hepatic mitochondrial synthesis of ketone bodies — acetoacetate, beta-hydroxybutyrate, and acetone — from acetyl-CoA during states of glucose scarcity.Sun, 06 Sep 2026 00:00:00 GMTmetabolic-physiologyDr. Helena Weisshttps://nutritionreference.org/glossary/ketosis/https://nutritionreference.org/glossary/ketosis/A metabolic state characterized by circulating ketone body concentrations above 0.5 mmol/L, reflecting hepatic ketogenesis from fatty acid oxidation during low glucose availability.Sun, 06 Sep 2026 00:00:00 GMTmetabolic-physiologyDr. Helena Weisshttps://nutritionreference.org/glossary/beta-hydroxybutyrate/https://nutritionreference.org/glossary/beta-hydroxybutyrate/The dominant circulating ketone body in fasting and ketogenic states, functioning as energy substrate, epigenetic regulator, and signaling molecule.Sun, 06 Sep 2026 00:00:00 GMTbiochemistryDr. Helena Weisshttps://nutritionreference.org/glossary/medium-chain-triglycerides/https://nutritionreference.org/glossary/medium-chain-triglycerides/Triglycerides composed of medium-chain fatty acids (C6-C12) that are absorbed via portal circulation rather than lymphatic chylomicrons and rapidly oxidized to ketones in liver.Sun, 06 Sep 2026 00:00:00 GMTmacronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/omega-3-fatty-acids/https://nutritionreference.org/glossary/omega-3-fatty-acids/A family of polyunsaturated fatty acids with the first double bond at the third carbon from the methyl end, including ALA, EPA, and DHA.Sun, 06 Sep 2026 00:00:00 GMTmicronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/epa/https://nutritionreference.org/glossary/epa/A 20-carbon omega-3 polyunsaturated fatty acid and precursor to 3-series prostaglandins and E-series resolvins, found primarily in marine sources.Sun, 06 Sep 2026 00:00:00 GMTmicronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/dha/https://nutritionreference.org/glossary/dha/A 22-carbon omega-3 polyunsaturated fatty acid concentrated in neural and retinal membranes, essential for normal brain and visual development.Sun, 06 Sep 2026 00:00:00 GMTmicronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/omega-6-fatty-acids/https://nutritionreference.org/glossary/omega-6-fatty-acids/Polyunsaturated fatty acids with the first double bond at the sixth carbon from the methyl end, with linoleic acid being the dietary precursor to arachidonic acid.Sun, 06 Sep 2026 00:00:00 GMTmicronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/saturated-fats/https://nutritionreference.org/glossary/saturated-fats/Fatty acids containing no carbon-carbon double bonds, typically solid at room temperature, found primarily in animal fats and tropical oils.Sun, 06 Sep 2026 00:00:00 GMTmacronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/monounsaturated-fats/https://nutritionreference.org/glossary/monounsaturated-fats/Fatty acids with exactly one carbon-carbon double bond, dominantly oleic acid (C18:1), characteristic of olive oil and the Mediterranean dietary pattern.Sun, 06 Sep 2026 00:00:00 GMTmacronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/polyunsaturated-fats/https://nutritionreference.org/glossary/polyunsaturated-fats/Fatty acids containing two or more carbon-carbon double bonds, encompassing the omega-3 and omega-6 families and including both essential dietary fatty acids.Sun, 06 Sep 2026 00:00:00 GMTmacronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/linoleic-acid/https://nutritionreference.org/glossary/linoleic-acid/An essential omega-6 polyunsaturated fatty acid with 18 carbons and two double bonds, the parent compound from which arachidonic acid is synthesized.Sun, 06 Sep 2026 00:00:00 GMTmacronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/alpha-linolenic-acid/https://nutritionreference.org/glossary/alpha-linolenic-acid/An essential omega-3 polyunsaturated fatty acid with 18 carbons and three double bonds, precursor to EPA and DHA.Sun, 06 Sep 2026 00:00:00 GMTmacronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/vitamin-d/https://nutritionreference.org/glossary/vitamin-d/A fat-soluble secosteroid essential for calcium and phosphate homeostasis, synthesized in skin from 7-dehydrocholesterol under UVB exposure or obtained from diet.Sun, 06 Sep 2026 00:00:00 GMTmicronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/vitamin-b12/https://nutritionreference.org/glossary/vitamin-b12/A cobalt-containing water-soluble vitamin essential for DNA synthesis, fatty acid metabolism, and myelin maintenance, obtained almost exclusively from animal-source foods.Sun, 06 Sep 2026 00:00:00 GMTmicronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/folate/https://nutritionreference.org/glossary/folate/A water-soluble B vitamin essential for one-carbon transfer reactions including thymidylate synthesis, methionine regeneration, and DNA methylation.Sun, 06 Sep 2026 00:00:00 GMTmicronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/iron/https://nutritionreference.org/glossary/iron/An essential trace mineral required for hemoglobin, myoglobin, cytochromes, and numerous iron-sulfur cluster enzymes, with absorption tightly regulated by body iron status.Sun, 06 Sep 2026 00:00:00 GMTmicronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/heme-vs-non-heme-iron/https://nutritionreference.org/glossary/heme-vs-non-heme-iron/The two dietary forms of iron with distinct absorption pathways — heme iron from animal-source foods with 15-35% bioavailability, non-heme iron from plant and fortified sources with 2-20% bioavailability.Sun, 06 Sep 2026 00:00:00 GMTmicronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/magnesium/https://nutritionreference.org/glossary/magnesium/An essential divalent cation cofactor for over 300 enzymatic reactions including ATP handling, DNA/RNA synthesis, and neuromuscular excitability regulation.Sun, 06 Sep 2026 00:00:00 GMTmicronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/zinc/https://nutritionreference.org/glossary/zinc/An essential trace mineral and structural/catalytic cofactor for over 300 enzymes and more than 2000 transcription factors, critical for immune function and growth.Sun, 06 Sep 2026 00:00:00 GMTmicronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/calcium/https://nutritionreference.org/glossary/calcium/The most abundant mineral in the human body, required for skeletal mineralization, neuromuscular function, blood coagulation, and intracellular signaling.Sun, 06 Sep 2026 00:00:00 GMTmicronutrient-scienceDr. Helena Weisshttps://nutritionreference.org/glossary/potassium/https://nutritionreference.org/glossary/potassium/The principal intracellular cation, essential for resting membrane potential, cardiac and neural excitability, and acid-base balance; consistently under-consumed in US diets.Sun, 06 Sep 2026 00:00:00 GMTmicronutrient-scienceDr. Helena Weiss