Adaptive Thermogenesis
A decrease in resting and non-resting metabolic expenditure that exceeds what can be predicted by the loss of body mass during prolonged caloric restriction. Often referred to colloquially as "metabolic adaptation."
Amino Acids
Organic compounds that combine to form proteins. The human body requires 20 amino acids, 9 of which are classified as essential because they cannot be synthesized endogenously and must be consumed via diet.
Basal Metabolic Rate (BMR)
The minimum amount of energy (calories) expended by the body to sustain vital vegetative functions (such as brain function, heartbeat, and cellular protein synthesis) in a completely rested, fasted state. Calculate yours using our BMR Calculator.
Body Recomposition
The simultaneous reduction of body adipose tissue (fat loss) and increase in skeletal muscle mass (hypertrophy), typically achieved via resistance training, high protein intake, and a slight caloric deficit or maintenance intake.
Caloric Deficit
A physiological state where the total energy consumed from food and beverage intake is lower than total daily energy expenditure (TDEE). This forces the body to mobilize stored endogenous triglycerides from adipose tissue for fuel.
Caloric Density (Energy Density)
The amount of energy (calories) per unit weight of food (kcal/gram). High-water and high-fiber foods (vegetables, fruits, lean meats) have low caloric density, allowing for greater physical stomach fullness with fewer total calories.
CICO (Calories In, Calories Out)
The scientific shorthand summarizing the first law of thermodynamics applied to human biology. Body mass alterations are fundamentally dictated by the net differential between metabolizable energy ingested and total energy dissipated.
Diet Break
A planned, strategic period of 1 to 2 weeks where an individual eating in a caloric deficit temporarily raises energy intake to maintenance levels. This attenuates diet fatigue, restores thyroid/leptin signaling, and reduces muscle loss.
Energy Balance
The relationship between energy intake (ingested calories) and energy expenditure (BMR + TEF + NEAT + EAT). A positive balance leads to weight gain; a negative balance produces weight loss; an equilibrium results in weight maintenance.
Ghrelin
An orexigenic peptide hormone produced primarily by cells in the gastrointestinal tract. Often dubbed the "hunger hormone," ghrelin levels rise before meals and during caloric deficits to stimulate appetite.
Glycogen
The primary stored carbohydrate in animal tissue, concentrated in skeletal muscle (~400-500g) and the liver (~80-100g). Each gram of stored glycogen binds approximately 3 to 4 grams of water.
Intermittent Fasting (IF)
An umbrella term for dietary timing patterns that cycle between voluntary periods of fasting and eating (e.g., 16:8, 18:6, OMAD, 5:2). Intermittent fasting simplifies calorie control and promotes metabolic flexibility. To track your fasting timer and autophagy stages in real-time, explore our companion platform at FastingTracker.net.
Leptin
An adipokine hormone secreted by fat cells that signals satiety and long-term energy stores to the hypothalamus. When body fat drops during dieting, circulating leptin decreases, prompting increased hunger.
Macronutrients (Macros)
Nutrients required in large quantities by the human body: Protein (4 kcal/g), Carbohydrates (4 kcal/g), and Dietary Fats (9 kcal/g). Calculate your macro split with our Macro Split Calculator.
Muscle Protein Synthesis (MPS)
The biochemical process where cells build new muscle proteins to repair and grow muscle tissue, triggered by essential amino acids (particularly leucine) and resistance training.
Non-Exercise Activity Thermogenesis (NEAT)
The energy expended for everything that is not sleeping, eating, or dedicated sports-like exercise. Includes pacing, fidgeting, yard work, and general daily movement. NEAT can vary by up to 800 kcal/day between individuals.
Reverse Dieting
The practice of gradually increasing daily caloric intake by small increments (50–100 kcal per week) following a prolonged fat loss diet to restore metabolic rate and hormonal balance while minimizing adipose rebound.
Satiety Index
A standardized clinical metric evaluating the capacity of specific foods to satisfy hunger and maintain fullness over a two-hour postprandial window relative to white bread (baseline 100%). Boiled potatoes, lean fish, and oatmeal rank among the highest.
Thermic Effect of Food (TEF)
The metabolic energy required for the digestion, absorption, and assimilation of dietary nutrients. Dietary protein boasts the highest TEF (20–30% of ingested energy), while carbohydrates require 5–10% and fats 0–3%.
Total Daily Energy Expenditure (TDEE)
The aggregate sum of all calories burned by an individual over a 24-hour period, calculated as: TDEE = BMR + TEF + NEAT + EAT. Calculate your personalized number using our TDEE Calculator.
