Fat Loss & Nutrition Glossary
Clear, science-backed definitions for every key term in fat loss, metabolism, training, and nutrition. Written and reviewed by our research team.
Metabolism
Basal Metabolic Rate (BMR)
The minimum number of calories your body needs per day at complete rest, with no digestion or activity, to maintain essential physiological functions.
Total Daily Energy Expenditure (TDEE)
The total number of calories you burn in a day, including BMR, activity, movement, and the thermic effect of food.
Non-Exercise Activity Thermogenesis (NEAT)
The calories you burn from everyday movement — walking, fidgeting, standing, doing chores — outside of formal exercise.
Thermic Effect of Food (TEF)
The energy cost of digesting, absorbing, and metabolizing food — typically 8–15% of calories consumed.
Metabolic Adaptation
The reduction in energy expenditure your body makes in response to prolonged calorie restriction, beyond what predicted equations explain.
Nutritional Ketosis
A metabolic state in which the liver produces ketone bodies from fat as an alternative fuel to glucose.
Autophagy
A cellular recycling process in which damaged components are broken down — upregulated by fasting and exercise.
Glycogen
The body's storage form of carbohydrate, held in the liver and muscles — the primary fuel for high-intensity exercise.
Nutrition
Calorie Deficit
Eating fewer calories than you burn, forcing the body to use stored energy (primarily fat) for fuel.
Macronutrient
The three calorie-providing nutrients: protein (4 kcal/g), carbohydrates (4 kcal/g), and fat (9 kcal/g).
Muscle Protein Synthesis (MPS)
The process by which the body builds new muscle protein, stimulated by resistance training and protein intake.
Net Carbs
Total carbohydrates minus fiber (and in some formulations, sugar alcohols) — the carbs that raise blood glucose.
Glycemic Index (GI)
A 0–100 score indicating how quickly a specific food raises blood glucose compared to pure glucose.
Glycemic Load (GL)
A portion-adjusted measure of how a food will affect blood sugar: GL = (GI × carb grams per serving) / 100.
DIAAS (Digestible Indispensable Amino Acid Score)
A modern protein-quality score that accounts for ileal digestibility of each essential amino acid.
Training
Progressive Overload
The training principle of gradually increasing stress (weight, reps, volume) to drive continued adaptation.
Training Volume
The total work performed in training, commonly measured as sets × reps × load or weekly hard sets per muscle group.
One-Rep Max (1RM)
The maximum weight you can lift for a single repetition with correct form.
Body Recomposition
Simultaneously losing fat and gaining muscle — most achievable for beginners, returnees, and higher-body-fat individuals.
Hormones & Physiology
Insulin Sensitivity
How efficiently your cells respond to insulin to absorb glucose from the bloodstream.
Polycystic Ovary Syndrome (PCOS)
A hormonal disorder affecting 8–13% of reproductive-age women, commonly featuring insulin resistance and fat-loss challenges.
Cortisol
A glucocorticoid hormone released by the adrenals during stress that, when chronically elevated, promotes central fat storage.
Sarcopenia
Age-related loss of muscle mass and strength, accelerating after 60 and a primary driver of metabolic decline.
Anabolic Resistance
The blunted muscle-protein-synthesis response to protein and training in older adults.
Relative Energy Deficiency in Sport (RED-S)
A syndrome of impaired physiological function caused by chronic under-fueling in athletes.
Menopause
The end of menstrual cycles, usually between ages 45–55, marked by declining estrogen and metabolic shifts.
Diet Types
IIFYM (If It Fits Your Macros)
A flexible-dieting approach where food choices are made freely as long as daily macro targets are met.
Ketogenic Diet
A very-low-carbohydrate, high-fat diet that shifts metabolism toward burning fat and ketones for fuel.
Intermittent Fasting (IF)
An eating pattern that alternates between fasting windows and eating windows — common protocols are 16:8, 18:6, and OMAD.
Measurement & Tools
Mifflin-St Jeor Equation
A validated formula that estimates BMR from weight, height, age, and sex — the most accurate equation for the general population.
Katch-McArdle Formula
A BMR formula that uses lean body mass directly, typically more accurate for athletic or low-body-fat individuals.
Lean Body Mass (LBM)
Your total body weight minus fat mass — includes muscle, bone, organs, and water.
Visceral Fat
Fat stored around internal organs in the abdominal cavity — the most metabolically active and health-damaging body fat.
Somatotype
William Sheldon's body-type classification (ectomorph, mesomorph, endomorph) — loosely correlated with training responses.