Nutrition Glossary

A

Adequate Intake (AI)

The recommended average daily intake level based on observed or experimentally-determined approximations of nutrient intake by a group of apparently healthy people. Used when an RDA cannot be determined due to insufficient evidence.

Alpha-Carotene

A provitamin A carotenoid found in orange and yellow vegetables. Less efficiently converted to vitamin A than beta-carotene (1 RAE = 24 µg alpha-carotene).

Amino Acid

Organic compounds that serve as the building blocks of proteins. Nine are essential (must come from diet): histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

Ascorbic Acid

The chemical name for vitamin C, a water-soluble vitamin and antioxidant essential for collagen synthesis, immune function, and iron absorption.

B

Beta-Carotene

The most important provitamin A carotenoid, found in orange and dark green vegetables. Converted to vitamin A in the body (1 RAE = 12 µg beta-carotene). Also functions as an antioxidant.

Bioavailability

The proportion of a nutrient that is absorbed from the diet and utilized for normal body functions. Varies by nutrient form, food matrix, cooking method, and individual factors such as gut health.

Body Mass Index (BMI)

A measure of body fat based on weight relative to height (kg/m²). Categories: underweight (<18.5), normal (18.5–24.9), overweight (25–29.9), obese (≥30). Used in population-level dietary risk assessment.

C

Calorie (kcal)

A unit of energy. In nutrition, 1 kilocalorie (kcal) equals the energy needed to raise 1 kg of water by 1°C. Protein and carbohydrates provide ~4 kcal/g, fat provides ~9 kcal/g, and alcohol provides ~7 kcal/g.

Carbohydrate

A macronutrient providing 4 kcal/g of energy. Includes sugars (simple), starches (complex), and dietary fiber. Found primarily in grains, fruits, vegetables, and legumes.

Carotenoid

A class of pigments found in plants, responsible for red, orange, and yellow colors. Some (beta-carotene, alpha-carotene, beta-cryptoxanthin) are provitamin A; others (lutein, zeaxanthin, lycopene) serve as antioxidants.

Cholesterol

A waxy lipid found in animal-derived foods and produced by the liver. Dietary cholesterol has a modest effect on blood cholesterol in most people. Essential for cell membranes, hormones, and bile acid production.

Cobalamin

The chemical name for vitamin B12, essential for red blood cell formation, neurological function, and DNA synthesis. Found exclusively in animal-derived foods and fortified products.

D

Daily Value (DV)

A reference amount of a nutrient used on food labels to indicate what percentage of the recommended daily intake one serving provides. Based on a 2,000 kcal/day diet for adults and children aged 4+.

Dietary Fiber

The indigestible portion of plant foods. Includes soluble fiber (oats, beans) which lowers cholesterol, and insoluble fiber (whole grains, vegetables) which aids digestion. AI is 25–38 g/day for adults.

Dietary Reference Intake (DRI)

A comprehensive system of nutrition recommendations from the National Academies. Includes four values: RDA, AI, UL, and EAR, specified by age group and sex.

DHA (Docosahexaenoic Acid)

A long-chain omega-3 fatty acid critical for brain development and retinal function. Found in fatty fish, algae, and fish oil supplements. Along with EPA, represents the most biologically active omega-3s.

E

EPA (Eicosapentaenoic Acid)

A long-chain omega-3 fatty acid with anti-inflammatory properties. Found primarily in fatty fish. Together with DHA, may reduce cardiovascular disease risk.

Essential Nutrient

A nutrient the body cannot synthesize in sufficient quantities and must obtain from food. Includes 9 amino acids, 2 fatty acids (LA and ALA), 13 vitamins, and ~15 minerals.

Estimated Average Requirement (EAR)

The average daily nutrient intake level estimated to meet the requirements of half the healthy individuals in a particular age and sex group. Used to derive the RDA (RDA = EAR × 1.2).

F

Fat (Total Lipid)

A macronutrient providing 9 kcal/g — the most energy-dense macronutrient. Includes saturated, monounsaturated, and polyunsaturated fatty acids. Essential for hormone production, cell structure, and fat-soluble vitamin absorption.

Folate (Vitamin B9)

A B vitamin essential for DNA synthesis and cell division. Critical during pregnancy to prevent neural tube defects. Found naturally in leafy greens, legumes, and liver. The synthetic form (folic acid) is used in supplements and fortified foods.

FoodData Central (FDC)

The USDA's integrated food composition database, providing nutrient data for foods. Includes Foundation Foods (lab-analyzed), SR Legacy (historical), and other datasets. The primary data source for the Human Nutrition Explorer.

Foundation Foods

The most analytically rigorous dataset in USDA FoodData Central, containing extensively lab-analyzed nutrients for minimally processed foods with statistical measures (mean, min, max, standard error, data points).

G

Global Burden of Disease (GBD)

A comprehensive study by the Institute for Health Metrics and Evaluation (IHME) that quantifies health loss from diseases, injuries, and risk factors worldwide. The GBD 2023 data powers the Diet & Disease section of this tool.

Glycemic Index (GI)

A ranking system (0–100) that measures how quickly a carbohydrate-containing food raises blood glucose. High GI (>70): white bread, sugary drinks. Low GI (<55): most fruits, legumes, whole grains.

H

Heme Iron

A form of iron found in animal-derived foods (meat, poultry, fish). Absorbed 2–3 times more efficiently than non-heme iron. Accounts for 40% of iron in meat.

I

INFOODS Tagname

A standardized system of abbreviations (e.g., PROCNT for protein, ENERC_KCAL for energy) developed by the International Network of Food Data Systems to enable cross-database nutrient comparison.

K

Kilojoule (kJ)

The SI unit of energy used in many countries instead of kilocalories. 1 kcal = 4.184 kJ. The Australian Food Composition Database (AFCD) uses kilojoules as its primary energy unit.

L

Lutein

A carotenoid pigment found in dark leafy greens (kale, spinach) and egg yolks. Accumulates in the macula of the eye and may protect against age-related macular degeneration. Often measured alongside zeaxanthin.

Lycopene

A red carotenoid pigment found in tomatoes, watermelon, and pink grapefruit. A potent antioxidant that may reduce prostate cancer risk. Bioavailability increases with cooking and fat co-consumption.

M

Macronutrient

Nutrients required in large amounts that provide energy: protein (4 kcal/g), carbohydrates (4 kcal/g), and fat (9 kcal/g). Water is sometimes included as a fourth macronutrient.

Menaquinone (Vitamin K2)

A form of vitamin K found in fermented foods and animal products. Subtypes include MK-4 (meat, eggs) through MK-13 (fermented foods like natto). Supports bone metabolism and cardiovascular health.

Micronutrient

Nutrients required in small amounts (milligrams or micrograms): vitamins and minerals. Essential for metabolic processes but do not provide calories directly. Deficiencies can cause specific diseases.

Monounsaturated Fatty Acid (MUFA)

A fatty acid with one double bond in its carbon chain. Found in olive oil, avocados, and nuts. May improve blood cholesterol levels when replacing saturated fat.

N

Niacin (Vitamin B3)

A B vitamin essential for energy metabolism and DNA repair. Found in meat, fish, legumes, and enriched grains. Severe deficiency causes pellagra (dermatitis, diarrhea, dementia).

Non-Heme Iron

A form of iron found in plant foods and fortified products. Less efficiently absorbed than heme iron but represents the majority of dietary iron. Absorption enhanced by vitamin C.

O

Omega-3 Fatty Acid

A family of polyunsaturated fatty acids with the first double bond at carbon 3. Includes ALA (plant-based), EPA, and DHA (marine). Anti-inflammatory; may reduce cardiovascular disease risk.

Omega-6 Fatty Acid

A family of polyunsaturated fatty acids with the first double bond at carbon 6. Includes linoleic acid (LA), the most abundant dietary PUFA. Found in vegetable oils, nuts, and seeds. Essential but pro-inflammatory in excess.

P

Phylloquinone (Vitamin K1)

The plant form of vitamin K, found in green leafy vegetables. Primary role is blood coagulation (clotting). The dominant form in most diets.

Polyunsaturated Fatty Acid (PUFA)

A fatty acid with two or more double bonds. Includes omega-3 and omega-6 families. Found in fish, flaxseed, walnuts, and vegetable oils. Two PUFAs are essential: LA (omega-6) and ALA (omega-3).

Protein

A macronutrient providing 4 kcal/g, composed of amino acid chains. Functions include tissue building/repair, enzymes, hormones, and immune function. RDA is 0.8 g/kg body weight for adults.

Provenance (Source Indicator)

In the Human Nutrition Explorer, a per-nutrient label showing which database provided the value: F = USDA Foundation Foods (primary), A = FSANZ AFCD (gap-filler), S = USDA SR Legacy (fallback).

R

Recommended Dietary Allowance (RDA)

The average daily dietary intake level sufficient to meet the nutrient requirements of 97–98% of healthy individuals in a particular age and sex group. Set at EAR + 2 standard deviations.

Retinol Activity Equivalent (RAE)

The standard unit for measuring vitamin A activity. 1 RAE = 1 µg retinol = 12 µg beta-carotene = 24 µg alpha-carotene or beta-cryptoxanthin. Replaced the older IU system.

Riboflavin (Vitamin B2)

A B vitamin essential for energy metabolism and antioxidant protection. Found in dairy products, eggs, lean meats, and green vegetables. Sensitive to light degradation.

S

Saturated Fatty Acid (SFA)

A fatty acid with no double bonds in its carbon chain. Found in animal fats, tropical oils (coconut, palm), and dairy. High intake associated with elevated LDL cholesterol.

SR Legacy (Standard Reference)

The USDA's historical food composition database containing ~7,800 foods with up to 150 nutrients. Released in 2018 as the final version. Now supplemented by Foundation Foods and FNDDS in FoodData Central.

T

Thiamin (Vitamin B1)

A B vitamin essential for carbohydrate metabolism and nerve function. Found in whole grains, pork, and legumes. Severe deficiency causes beriberi (peripheral neuropathy, heart failure).

Tocopherol (Vitamin E)

A fat-soluble antioxidant vitamin. Alpha-tocopherol is the most biologically active form. Found in vegetable oils, nuts, seeds, and leafy greens. Protects cell membranes from oxidative damage.

Trans Fatty Acid

An unsaturated fatty acid with at least one double bond in trans configuration. Industrial trans fats (partially hydrogenated oils) strongly increase cardiovascular disease risk. Now largely banned in food production.

U

Tolerable Upper Intake Level (UL)

The highest average daily nutrient intake level likely to pose no risk of adverse health effects. Exceeding the UL increases the risk of toxicity. Not all nutrients have established ULs.

V

Vitamin

An organic micronutrient essential in small amounts for normal metabolism. Thirteen vitamins: four fat-soluble (A, D, E, K) and nine water-soluble (C and eight B vitamins). Most must come from diet.

W

Water-Soluble Vitamin

Vitamins that dissolve in water and are not stored in significant amounts: vitamin C and the eight B vitamins. Must be consumed regularly. Excess amounts are typically excreted in urine.

Z

Zeaxanthin

A carotenoid pigment found in corn, orange peppers, and egg yolks. Along with lutein, it accumulates in the macula of the eye and may protect against age-related macular degeneration and cataracts.

Zinc

An essential mineral required for immune function, wound healing, DNA synthesis, and taste perception. Found in meat, shellfish, legumes, and seeds. RDA is 8–11 mg/day for adults.