Glossary
Short definitions of the metabolism and nutrition terms that come up across the calculators and guides on this site. Each entry is linked from the articles that reference it.
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Term
The anabolic window is the period after exercise when the body is most receptive to nutrients for recovery and muscle protein synthesis. The original 30-minute window concept has been substantially revised by current research; the practical window is closer to 2-4 hours.
Read definitionBMR
BMR is the number of calories your body burns at complete rest, in a thermoneutral environment, in a fasted state. It represents the energy cost of keeping organs, brain, and basic biological processes running.
Read definitionBF%
Body fat percentage is the proportion of total body weight that comes from fat tissue, expressed as a percentage. It separates fat mass from lean mass (muscle, bone, water, organs) and is a more useful body composition signal than weight or BMI alone for fitness goals.
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Body recomposition is the simultaneous loss of body fat and gain of lean mass without large net changes in body weight. It is hardest for lean, trained adults and easiest for novice trainees, returning lifters, and adults with substantial fat to lose.
Read definitionkcal
A calorie is a unit of energy. In nutrition contexts, 'calorie' almost always refers to a kilocalorie (kcal): the amount of energy needed to raise one kilogram of water by one degree Celsius. The 'calorie' on food labels and the 'kcal' used in research are the same unit.
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Creatine is one of the most-studied supplements in sports nutrition. Creatine monohydrate at 3-5 g per day improves strength, power output, and high-intensity performance for most users. The effect is small but reliable, and the safety profile is among the best of any sports supplement.
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A diet break is a planned 1-2 week pause from a calorie deficit, eating at maintenance instead of below it. Research suggests structured breaks during long fat-loss blocks produce more total fat loss than continuous dieting at the same average deficit.
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Dietary fiber is the part of plant foods that passes through the digestive tract largely unabsorbed. Soluble fiber forms a gel that slows digestion; insoluble fiber adds bulk and supports gut motility. Most adults under-consume fiber, with the average US intake at roughly half the recommended daily target.
Read definitionGI
Glycemic index is a 0-100 scale that ranks carbohydrate-containing foods by how quickly they raise blood glucose, anchored against pure glucose (GI 100). GI is widely cited but less practically useful than glycemic load (GL), which accounts for actual carb amount in a real-world serving.
Read definitionGL
Glycemic load is a measure of how much a typical serving of a food raises blood glucose. It combines the food's glycemic index (which describes the speed of glucose response) with the actual carbohydrate amount in a real-world serving.
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Glycogen is the body's stored form of carbohydrate, held mostly in the liver and muscles. Each gram of glycogen carries roughly 3 grams of bound water, which is why low-carb diets and calorie cuts produce rapid early weight loss that is mostly water and stored carbs, not fat.
Read definitionIF
Intermittent fasting is an eating pattern that restricts food intake to specific windows of the day or week. The most common version is 16:8 (16 hours fasting, 8 hours eating). The mechanism for fat loss is calorie reduction; fasting itself does not burn fat differently than non-fasting eating at matched calories.
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The leucine threshold is the minimum amount of the amino acid leucine in a single meal needed to maximally stimulate muscle protein synthesis. Research suggests roughly 2.5-3 grams of leucine per meal, equivalent to roughly 25-30 grams of high-quality protein.
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Metabolic adaptation is the body's downward shift in energy expenditure during sustained calorie restriction. It is the legitimate phenomenon underneath the popular 'starvation mode' framing. The effect is real but usually smaller than dieting folklore suggests.
Read definitionMPS
Muscle protein synthesis is the process by which the body builds new muscle protein from amino acids. MPS responds to two main signals: resistance training (mechanical load) and protein ingestion (especially leucine). Net muscle gain happens when MPS exceeds muscle protein breakdown over time.
Read definitionNEAT
NEAT is the energy spent on movement that is not formal exercise: walking, fidgeting, posture, household activity, occupational movement. It is the most variable component of total daily energy expenditure between two similar-sized people.
Read definitionTerm
A refeed is a planned high-carb day during a sustained calorie deficit, used to restore glycogen, briefly elevate leptin, and provide psychological relief. Refeeds are shorter and more carb-focused than diet breaks; both are tools for managing the cost of long fat-loss blocks.
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Satiety is the feeling of fullness and the cessation of hunger after eating. It is influenced by food volume, protein and fiber content, eating speed, and hormonal signals (leptin, ghrelin, GLP-1, CCK). Different foods produce very different satiety responses per calorie.
Read definitionTEF
TEF is the energy your body spends digesting, absorbing, and metabolizing what you eat. It is roughly 8-10% of total daily energy expenditure for typical mixed diets, with notable variation by macronutrient composition.
Read definitionTDEE
TDEE is the estimated total number of calories you burn in a typical 24-hour day, including resting metabolism, the thermic effect of food, planned exercise, and incidental movement.
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