Glossary
Plain-English definitions of 30 terms covering nutrition science, metabolism, AI food tracking, GLP-1 medications, and dietary assessment methodology.
Measurement
24-Hour Recall
A 24-hour recall is a structured dietary assessment interview in which a trained interviewer asks the respondent to describe in detail every food and beverage consumed in the previous 24 hours, along with portion sizes and preparation methods. The Automated Multiple-Pass Method, used in NHANES, is the standard protocol for high-quality 24-hour recalls.
Dietary Assessment
Dietary assessment is the systematic measurement of an individual's or population's food and nutrient intake using structured methods such as 24-hour recalls, food frequency questionnaires, food records, or biomarkers. Each method has known accuracy and bias limitations; dietary assessment underpins clinical nutrition, public health surveillance, and the validation of consumer calorie tracking apps.
Food Frequency Questionnaire
A food frequency questionnaire (FFQ) is a structured dietary assessment instrument that asks respondents how often they consumed each of a defined list of foods over a specified period (typically the past month or year). FFQs are designed to estimate usual long-term intake patterns and are widely used in nutritional epidemiology, but carry known portion estimation and recall biases.
MAPE
Mean Absolute Percentage Error (MAPE) is a statistical measure of forecasting or estimation accuracy expressed as the average absolute percentage difference between predicted and reference values. In nutrition app evaluation, MAPE quantifies how closely a calorie tracking app's estimates match weighed reference values across a set of test meals; lower MAPE indicates better accuracy.
App & Tech
Barcode Scanning
Barcode scanning in calorie tracking apps is the use of a phone camera to read the UPC or EAN barcode on a packaged food product, which the app then maps to a database entry containing the manufacturer's published nutrition facts. Barcode scanning is the most accurate input method for packaged foods but does not work for fresh, prepared, or restaurant items.
Food Database
A food database is a structured collection of foods and their nutrient compositions used by calorie tracking apps, dietitians, and research instruments to convert food intake into calorie and nutrient values. Major sources include USDA FoodData Central (US), CIQUAL (France), McCance and Widdowson (UK), and proprietary app databases that blend public sources with user contributions.
Food Photo Recognition
Food photo recognition is the use of computer vision and deep learning to identify foods, estimate portion sizes, and compute calorie and macronutrient content from a single photograph. Modern systems combine convolutional neural networks (or vision transformers) for food identification with depth estimation, reference-object scaling, or multi-angle inference for portion estimation.
USDA FoodData Central
USDA FoodData Central (FDC) is the United States Department of Agriculture's integrated public food composition database, launched in 2019 to consolidate previously separate USDA databases. It contains laboratory-analyzed nutrient values for foundation foods, the SR Legacy reference set, branded foods, the FNDDS dataset for dietary assessment, and experimental food data.
Metabolism
BMR
Basal Metabolic Rate (BMR) is the minimum number of calories the human body requires to sustain vital functions while completely at rest, fasted, and in a thermoneutral environment. BMR represents the energy cost of organ function, cellular maintenance, and core body temperature, and accounts for 60-75% of total daily energy expenditure in most adults.
NEAT
Non-Exercise Activity Thermogenesis (NEAT) is the energy expended for everything other than sleeping, eating, or formal exercise — including standing, walking to the mailbox, fidgeting, typing, household chores, and occupational activity. NEAT can vary by 2,000 kcal per day between individuals of similar body size and is the most variable component of total daily energy expenditure.
RMR
Resting Metabolic Rate (RMR) is the number of calories the body burns at rest, measured under standard but less stringent conditions than BMR. RMR includes minor energy costs of digestion, postural muscle tone, and recent activity, and is typically 5-10% higher than true BMR. Most clinical calorimetry measures RMR rather than BMR.
TDEE
Total Daily Energy Expenditure (TDEE) is the total number of calories a person burns in 24 hours. It is the sum of basal metabolic rate (BMR), the thermic effect of food (TEF), the energy cost of exercise (EAT), and non-exercise activity thermogenesis (NEAT). TDEE is the calorie target most weight management apps estimate to set deficits or surpluses.
Thermic Effect of Food
The thermic effect of food (TEF), also called diet-induced thermogenesis, is the energy the body expends to digest, absorb, and metabolize ingested nutrients. TEF accounts for approximately 10% of total daily energy expenditure on a mixed diet, but the percentage varies by macronutrient: protein costs 20-30% of its energy, carbohydrate 5-10%, and fat 0-3%.
Nutrition Science
Calorie
A calorie is a unit of energy equal to the amount of heat required to raise the temperature of one gram of water by one degree Celsius. In nutrition, the term refers almost exclusively to the kilocalorie (kcal), which is 1,000 small calories and represents the energy a food provides when metabolized.
Glycemic Index
The glycemic index (GI) is a numerical scale that ranks carbohydrate-containing foods by how quickly they raise blood glucose after consumption, relative to a reference food (usually pure glucose, set at 100). Foods are classified as low (≤55), medium (56-69), or high (≥70) GI based on standardized two-hour blood glucose response curves.
Glycemic Load
Glycemic load (GL) is a measure of the total impact of a food's carbohydrate content on blood glucose, accounting for both the carbohydrate quality (glycemic index) and the quantity consumed in a typical serving. GL is calculated as the glycemic index multiplied by grams of available carbohydrate per serving, divided by 100.
Macronutrient
A macronutrient is a class of nutrient required by the human body in large amounts (grams per day) to provide energy and structural material. The three dietary macronutrients are carbohydrate, protein, and fat; alcohol is sometimes counted as a fourth because it provides energy, although it is not nutritionally essential.
Micronutrient
A micronutrient is a nutrient required by the body in small amounts (milligrams or micrograms per day) for normal physiological function. Micronutrients include vitamins and minerals; they do not supply energy directly but are essential cofactors for the metabolic processes that release energy from macronutrients.
Net Carbs
Net carbs is an unofficial nutritional metric calculated by subtracting fiber and sugar alcohols from total carbohydrates on a food label. The concept is intended to estimate the carbohydrate fraction that meaningfully raises blood glucose, but the term has no FDA-recognized regulatory definition and is used inconsistently across the industry.
Protein Leverage Hypothesis
The protein leverage hypothesis is a theoretical framework proposing that humans regulate food intake primarily to meet a target absolute protein intake, and that when dietary protein density is diluted (as in modern ultra-processed food environments), individuals overconsume total energy in pursuit of that protein target. It was articulated by Simpson and Raubenheimer in 2005.
Satiety Index
The satiety index is a numerical ranking of how filling individual foods are per calorie consumed, originally developed by Susanna Holt and colleagues at the University of Sydney in 1995. Foods are scored relative to white bread (set at 100); a higher index indicates greater satiety per calorie. Boiled potatoes scored highest in the original study at 323.
Diet Method
Carb Cycling
Carb cycling is a structured dietary practice in which carbohydrate intake is varied across days or weeks based on training demand, performance goals, or body composition objectives. High-carb days are typically aligned with high-volume training; low-carb days with rest or low-volume training. Carb cycling is most established in physique sport and endurance training.
Intermittent Fasting
Intermittent fasting (IF) is an umbrella term for eating patterns that cycle between periods of eating and voluntary fasting. Common protocols include 16:8 time-restricted eating, alternate-day fasting, the 5:2 diet (two low-calorie days per week), and 24-hour periodic fasts. Most clinical trials show IF produces weight loss similar to calorie-equivalent continuous restriction.
Refeed Day
A refeed day is a planned, single-day or two-day increase in calorie intake — primarily from carbohydrate — built into an extended calorie deficit to replenish muscle glycogen, normalize leptin signaling, and improve psychological adherence. Refeeds are most commonly used in physique sport, athletic training during cuts, and structured weight-loss protocols.
Time-Restricted Eating
Time-restricted eating (TRE) is a form of intermittent fasting in which all daily food intake is confined to a fixed window of typically 6 to 12 hours, with the remaining hours spent fasting. The most popular protocol is 16:8 (16-hour fast, 8-hour eating window). TRE is studied for both weight management and circadian metabolic effects.
Pharmacology
GLP-1 Receptor Agonist
A GLP-1 receptor agonist is a class of injectable medication that mimics glucagon-like peptide-1, a gut hormone that stimulates insulin secretion, suppresses glucagon, slows gastric emptying, and reduces appetite. GLP-1 receptor agonists are FDA-approved for type 2 diabetes and chronic weight management; major branded products include semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound).
Mounjaro
Mounjaro is the brand name of subcutaneous tirzepatide manufactured by Eli Lilly, FDA-approved in 2022 for the treatment of type 2 diabetes. It is administered once weekly at doses of 2.5 mg through 15 mg via prefilled pen injector. Mounjaro is not FDA-approved for weight loss; the same molecule is sold as Zepbound for chronic weight management.
Ozempic
Ozempic is the brand name of subcutaneous semaglutide manufactured by Novo Nordisk, FDA-approved in 2017 for the treatment of type 2 diabetes. It is administered once weekly at doses of 0.25 mg, 0.5 mg, 1 mg, or 2 mg via prefilled pen injector. Ozempic is not FDA-approved for weight loss; the same molecule at a higher dose is sold as Wegovy for chronic weight management.
Semaglutide
Semaglutide is a long-acting GLP-1 receptor agonist developed by Novo Nordisk and FDA-approved under three brand names: Ozempic (subcutaneous, type 2 diabetes), Wegovy (subcutaneous, chronic weight management), and Rybelsus (oral, type 2 diabetes). It is administered as a once-weekly injection at doses ranging from 0.25 mg to 2.4 mg.
Tirzepatide
Tirzepatide is a dual GIP and GLP-1 receptor agonist developed by Eli Lilly, FDA-approved as Mounjaro for type 2 diabetes (2022) and as Zepbound for chronic weight management (2023). It is a once-weekly subcutaneous injection at doses from 2.5 mg to 15 mg, and has produced larger weight loss than semaglutide in head-to-head trials.