| BMR share of TDEE | ~60–75% (General physiological estimates; varies by individual) |
| Thermic effect of protein | 20–30% of calories consumed (Compared to 5–10% for carbohydrate and 0–3% for fat) |
| BMI categories defined by | WHO and CDC (Used for population screening, not individual diagnosis) |
| Key hunger-suppressing hormone | Leptin (Produced by adipose tissue; signals fullness to the brain) |
| Key hunger-stimulating hormone | Ghrelin (Rises before meals and during caloric restriction) |
| Adaptive thermogenesis can reduce | Metabolic rate by up to ~15% (Estimated range from controlled weight-loss research; individual variation applies) |
Why This Reference Exists
Weight management discussions are filled with acronyms, clinical terms, and concepts borrowed from physiology and nutrition science. Without a solid grasp of what these words actually mean, it's easy to misread health content — or be misled by it. This reference defines the terms that appear most frequently, clearly and without judgment.
For a deeper look at how energy metabolism works in practice, see our Metabolism & Energy hub. If you're also navigating fitness terminology for the first time, Key Terms Every Beginner Should Know Before Starting a Workout Plan covers the exercise side of the language gap.
Basal Metabolic Rate (BMR)
The number of calories the body requires at complete rest to maintain essential functions like breathing and circulation. It forms the baseline of daily energy expenditure calculations.
Total Daily Energy Expenditure (TDEE)
The estimated total calories burned in a day, combining resting metabolic rate with the energy cost of all physical activity and digestion.
Energy Balance
The relationship between calories consumed through food and calories expended through metabolism and activity. Positive balance means more consumed than burned; negative means more burned than consumed.
Body Composition
The proportion of fat mass, lean mass, and other tissues that make up total body weight. More informative than weight alone for assessing health and fitness status.
Visceral Fat
Fat stored within the abdominal cavity around internal organs. Metabolically distinct from subcutaneous fat and more strongly linked to certain cardiometabolic risk factors.
Set Point Theory
A hypothesis suggesting the body regulates its weight within a preferred range through hormonal and metabolic feedback mechanisms. Still debated, but useful for understanding weight regulation biology.
Adaptive Thermogenesis
A reduction in metabolic rate that occurs in response to sustained caloric restriction. It is a physiological adaptation, not an indicator of personal effort or willpower.
Insulin Sensitivity
A measure of how effectively the body's cells respond to insulin signals to take up glucose from the bloodstream. Higher sensitivity is generally associated with better metabolic health.
Thermic Effect of Food (TEF)
The energy the body expends to digest, absorb, and process nutrients. It typically accounts for roughly 10% of total daily energy expenditure, varying by macronutrient type.
Satiety
The sustained sense of fullness between meals that reduces the drive to eat again. Regulated by hormones such as leptin and peptide YY acting on the brain and digestive system.
Lean Mass
All body tissue excluding fat mass — including muscle, bone, connective tissue, organs, and fluids. Often used as a proxy for metabolically active tissue.
Body Mass Index (BMI)
A simple ratio of weight to height squared used as a population-level screening tool. Useful for broad comparisons but does not measure body composition or account for individual variation.
Core Metabolic and Energy Terms
These are the terms you'll encounter most often when reading about how the body uses and stores energy.
| BMR share of TDEE | ~60–75% (General physiological estimates; varies by individual) |
| Thermic effect of protein | 20–30% of calories consumed (Compared to 5–10% for carbohydrate and 0–3% for fat) |
| BMI categories defined by | WHO and CDC (Used for population screening, not individual diagnosis) |
| Key hunger-suppressing hormone | Leptin (Produced by adipose tissue; signals fullness to the brain) |
| Key hunger-stimulating hormone | Ghrelin (Rises before meals and during caloric restriction) |
| Adaptive thermogenesis can reduce | Metabolic rate by up to ~15% (Estimated range from controlled weight-loss research; individual variation applies) |
Basal Metabolic Rate (BMR) refers to the calories your body burns at complete rest just to sustain basic functions — breathing, circulation, and cell maintenance. It does not include any activity. Resting Metabolic Rate (RMR) is a closely related measure taken under slightly less strict conditions; the two terms are often used interchangeably in general health content, though they differ methodologically. Total Daily Energy Expenditure (TDEE) adds all activity on top of your RMR to estimate total caloric need for the day. For a detailed comparison of these three numbers, see Basal Metabolic Rate, TDEE, and RMR: A Plain-Language Guide.
Energy balance describes the relationship between calories consumed and calories expended. A positive energy balance means more is consumed than burned; a negative balance means the reverse. Neither state is inherently good or bad — context and duration matter considerably.
Thermic effect of food (TEF) is the energy cost of digesting, absorbing, and metabolizing nutrients. Protein generally has a higher TEF than fat or carbohydrate, meaning the body expends more energy processing it.
Body Composition and Weight Distribution Terms
Body composition refers to the proportions of fat mass, lean mass (muscle, bone, organs, water), and other tissues in the body. Weight alone does not capture this distinction. Two people at the same weight can have very different body compositions and health profiles. Understanding Body Composition: A Starter Guide explores this in more depth.
Fat mass is the total weight of adipose (fat) tissue. Lean mass encompasses everything else — muscle, connective tissue, organs, and fluids. Fat-free mass is sometimes used as a synonym for lean mass, though the terms are not always identical across studies.
Visceral fat accumulates around internal organs in the abdominal cavity. It is metabolically distinct from subcutaneous fat, which sits just beneath the skin. Research suggests visceral fat is more strongly associated with certain metabolic risk factors, though individuals have limited direct control over fat distribution patterns, which are influenced by genetics, hormones, and age.
BMI (Body Mass Index) is a ratio of weight to height squared (kg/m²) used as a population-level screening tool. It is widely used because it requires no special equipment, but it does not measure body composition directly and has well-documented limitations when applied to individuals.
Behavioral and Physiological Concepts
Set point theory is the hypothesis that the body has a biologically preferred weight range it actively defends through hormonal and metabolic adjustments. The evidence base is ongoing and debated, but the theory helps explain why sustained weight change can be physiologically challenging for many people.
Adaptive thermogenesis describes the body's tendency to reduce energy expenditure in response to prolonged caloric restriction — a biological mechanism, not a personal failing. Understanding this concept is important for interpreting why weight loss can slow over time independent of effort.
Satiety is the feeling of fullness and satisfaction after eating that suppresses further intake. Satiation refers to the signals that end a meal. Both are regulated by a complex interplay of hormones, including leptin, ghrelin, and peptide YY.
Insulin sensitivity describes how effectively cells respond to insulin's signal to absorb glucose. Insulin resistance — when that response is blunted — is associated with several metabolic conditions and is influenced by factors including physical activity, sleep quality, and body composition.
For guidance on how physical activity interacts with these systems, see Physical Activity Guidelines for Adults: A Plain-English Breakdown.
This article is for general informational purposes only and does not constitute medical advice. Consult a qualified healthcare professional for guidance specific to your health situation.