Health.
Glossary

A measure of body size calculated from weight and height: BMI = weight (kg) ÷ height (m)². BMI classifications: Under 18.5 = Underweight, 18.5–24.9 = Normal weight, 25–29.9 = Overweight, 30+ = Obese. BMI is a population-level screening tool; it cannot distinguish between fat mass and muscle mass, making it unreliable for athletes and muscular individuals.

The proportion of total body mass that is adipose (fat) tissue, expressed as a percentage. More meaningful than BMI for assessing health and fitness because it distinguishes between fat mass and lean mass. Healthy ranges: Men 8–19%, Women 21–33%. Measured by DEXA scan (gold standard), hydrostatic weighing, or estimated by circumference-based methods like the Navy Method.

Total body weight minus fat mass. Includes muscles, bones, organs, water, and connective tissue. Lean body mass is used in some metabolic rate calculations as a more precise predictor of caloric needs than total body weight, since fat tissue is metabolically less active than muscle.

Fat stored within the abdominal cavity surrounding internal organs, as opposed to subcutaneous fat stored under the skin. Visceral fat is metabolically active and associated with higher cardiovascular and metabolic disease risk. It is not visible externally and cannot be measured accurately by BMI or simple circumference measurements.

Waist circumference divided by height, both in the same units. A ratio above 0.5 indicates excess central body fat at any age. Some researchers consider waist-to-height ratio a more reliable cardiovascular risk predictor than BMI because it specifically captures central obesity, which carries higher health risk than distributed body fat.

The number of calories your body requires per day at complete rest to maintain basic physiological functions — breathing, circulation, cell production, organ function. BMR represents 60–75% of total daily caloric expenditure for sedentary individuals. It decreases with age and increases with lean body mass.

The most widely validated formula for estimating BMR. For men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5. For women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161. Published in 1990 and validated across diverse populations; more accurate than the older Harris-Benedict equation.

The total number of calories you burn in a day, including all physical activity. Calculated by multiplying BMR by an activity multiplier: Sedentary (desk job, no exercise) × 1.2; Lightly active (1–3 days exercise) × 1.375; Moderately active (3–5 days) × 1.55; Very active (6–7 days hard exercise) × 1.725. Eating at TDEE maintains current weight.

The Physical Activity Level multiplier applied to BMR to calculate TDEE. Ranges from 1.2 (sedentary) to 1.9 (extremely active manual labour plus intense exercise). Choosing the correct multiplier is the main source of error in TDEE estimation — most people overestimate their activity level.

Similar to BMR but measured under slightly less strict conditions (fasting but not necessarily post-sleep). REE is typically 10% higher than BMR. The terms are often used interchangeably in non-clinical contexts, though they are technically distinct measurements.

Calories burned through all physical activity that is not formal exercise — walking, standing, fidgeting, household tasks. NEAT is highly variable between individuals (ranging from near zero to over 2,000 kcal/day) and is the primary reason two people with the same BMR can have very different TDEE values.

The reduction in metabolic rate that occurs in response to prolonged caloric restriction. The body reduces energy expenditure to conserve resources, making weight loss progressively harder over time at the same caloric deficit. This is why TDEE should be recalculated periodically during a weight loss programme.

The three primary categories of nutrients that provide energy: protein (4 calories per gram), carbohydrates (4 calories per gram), and fat (9 calories per gram). Macronutrient ratios determine the character of a diet (high-protein, low-carb, ketogenic, etc.) beyond raw caloric intake.

A macronutrient essential for muscle protein synthesis, enzyme production, and tissue repair. Provides 4 kcal/gram. Recommended intake for muscle maintenance during a caloric deficit: 0.8–1.0g per pound of body weight (1.8–2.2g/kg). Protein is more satiating per calorie than carbohydrates or fat.

The primary fuel source for high-intensity exercise and the brain. Provides 4 kcal/gram. Stored as glycogen in muscle and liver. Unlike protein and fat, carbohydrates are not essential nutrients — the body can function without them, though athletic performance typically declines.

An essential macronutrient required for hormone production (including testosterone and estrogen), fat-soluble vitamin absorption (A, D, E, K), and cell membrane integrity. Provides 9 kcal/gram. A minimum of 0.3–0.4g per pound of body weight is required to maintain hormonal health.

Consuming fewer calories than TDEE, causing the body to use stored energy (primarily fat) for fuel. A deficit of 500 kcal/day theoretically produces approximately 1 lb of fat loss per week. Aggressive deficits (over 1,000 kcal/day) increase muscle loss and metabolic adaptation.

Consuming more calories than TDEE, providing the energy needed for muscle protein synthesis and growth. For muscle gain (bulking), a modest surplus of 200–500 kcal above TDEE minimises fat gain while supporting muscle growth.

A unit of energy. In nutrition, "calorie" refers to a kilocalorie (kcal) — the energy needed to raise the temperature of 1 kg of water by 1°C. All macronutrient calorie values (protein = 4 kcal/g, carbohydrate = 4 kcal/g, fat = 9 kcal/g) use this unit.