The nutrition glossary

The most popular intermittent fasting protocol. Fast for 16 hours, eat within an 8-hour window each day. Typical eating window 12 PM to 8 PM. Mizushima 2008 and Patterson and Sears 2017 are foundational references.

A weekly intermittent fasting protocol: eat normally for 5 days, restrict to ~500 to 600 kcal on 2 non-consecutive days. Easier adherence than daily fasting; weekly calorie deficit ~14 to 18%.

A factor that scales Basal Metabolic Rate to estimate Total Daily Energy Expenditure. Standard values range from 1.2 (sedentary) to 1.9 (extra active). Also called Physical Activity Level (PAL).

Sugars added to foods during processing (different from sugars naturally present in fruit or milk). The AHA recommends ≤25 g/day for adult women and ≤36 g/day for adult men.

A rare sugar (D-psicose) that tastes ~70% as sweet as sucrose but provides only 0.4 kcal/g and does not raise blood glucose. FDA exempts it from "Total Sugars" labeling.

The 20 building blocks that proteins are made of. Nine are essential and must come from food; the body synthesizes the rest. Sequence and ratio of amino acids determine a protein's biological role.

The post-workout period (historically claimed at 30 to 60 minutes) when protein consumption supposedly maximizes muscle protein synthesis. Modern research (Schoenfeld et al.) shows the window is much wider, generally hours.

A high-intensity artificial sweetener about 200× sweeter than sucrose. Used in diet sodas and sugar-free products. FDA-approved; the WHO classified it Group 2B "possibly carcinogenic" in 2023 at high doses.

A cellular self-cleaning process where the body breaks down and recycles damaged proteins and organelles. Upregulated by fasting, generally starting around the 16-hour mark in humans. Mizushima 2008 (Cell) is the foundational review. Cheng 2014 documented stem-cell regeneration during prolonged fasts.

Calories your body burns at rest to keep vital functions running (breathing, circulation, temperature, cell repair). For most people, BMR accounts for 60 to 70% of total daily energy expenditure.

How much of a nutrient is absorbed and used by the body after eating. Affected by digestion, food matrix, cooking, and individual factors. Animal proteins typically have higher bioavailability than most plant proteins.

A screening metric calculated as weight in kilograms divided by height in meters squared. BMI categories: Underweight <18.5, Normal 18.5 to 24.9, Overweight 25 to 29.9, Obese ≥30. Does not distinguish muscle from fat.

Three essential amino acids (leucine, isoleucine, and valine) that share a branched molecular structure. Leucine is the primary trigger of muscle protein synthesis among the three.

A central nervous system stimulant that blocks adenosine receptors, reducing perceived tiredness. FDA-considered safe up to 400 mg/day for healthy adults (~4 cups of coffee).

The time for the body to eliminate half of a caffeine dose. Average ~5 hours in healthy adults; longer in pregnancy, with hormonal birth control, or for slow metabolizers (CYP1A2 variant).

The acute toxic dose of caffeine. Severe symptoms (seizures, arrhythmia, vomiting) typically begin around 150 mg/kg of body weight. Estimated lethal dose (LD50) in humans is ~150 to 200 mg/kg, equivalent to roughly 80 to 100 cups of brewed coffee in a single sitting for a 70 kg adult. The FDA recommended daily limit (400 mg) is far below this threshold.

The most abundant mineral in the body, critical for bone health, muscle contraction, and nerve signaling. RDA: 1,000 mg/day for most adults, 1,200 mg/day for women over 50.

Eating fewer calories than you burn. About 7,700 kcal of deficit equals one kilogram of body fat loss (3,500 kcal per pound). Sustainable deficits sit between 250 and 750 kcal/day for most adults.

Eating more calories than you burn. A surplus of 250 to 500 kcal/day supports lean muscle gain with minimal fat gain when paired with resistance training and adequate protein.

A macronutrient providing 4 kcal per gram. Includes sugars, starches, and fiber. The body breaks most carbs down to glucose, the primary fuel for the brain and high-intensity exercise.

A slow-digesting milk protein (about 80% of total cow's-milk protein) that clots in the stomach and releases amino acids over 4 to 7 hours. DIAAS ~1.18. Popular as a pre-sleep protein source.

The process of dissolving soluble compounds from coffee grounds into water. Specialty Coffee Association (SCA) target is 18 to 22% extraction yield by mass for hot brew. Cold brew extracts more slowly and selectively. Higher extraction increases caffeine and bitterness; lower yields a sweeter, less bitter cup.

Coffee brewed by steeping coarse grounds in cold water for 12 to 24 hours. Lower in acidity and bitterness than hot brew. Concentrate ratios typically range from 1:3 (extra strong) to 1:8 (ready-to-drink). Caffeine extraction is around 12 mg per gram of dry beans with ~85% efficiency over a 16 hour steep.

A protein source that contains all nine essential amino acids in sufficient amounts. Animal sources are complete by default. Plant-based combinations (rice + beans, soy, quinoa) can also be complete.

The Adequate Intake set by the U.S. National Academies of Sciences (NAS, 2005) for total daily water from all sources (drinks plus food). About 91 oz (2.7 L) per day for adult women and 125 oz (3.7 L) per day for adult men. Pregnancy adds about 10 oz, breastfeeding adds about 32 oz.

Digestible Indispensable Amino Acid Score. The FAO's 2013 standard for protein quality, replacing PDCAAS. Scores can exceed 1.0 (whey 1.09, casein 1.18). Higher is better.

A macronutrient providing 9 kcal per gram, the most calorie-dense of the three. Essential for hormone production, vitamin absorption (A, D, E, K), and cell membranes.

Plant-based carbohydrate the body cannot fully digest. The USDA recommends 14 grams of fiber per 1,000 kcal consumed. Supports gut health, satiety, and blood sugar control.

The portion of the day during which an intermittent faster consumes all of their calories. Common windows are 8 hours (16:8), 6 hours (18:6), 4 hours (20:4), or 1 hour (OMAD). The complement is the "fasting window."

Minerals that carry an electric charge in body fluids. The main ones are sodium, potassium, chloride, magnesium, calcium, and phosphate. Critical for nerve signaling, muscle contraction, and fluid balance.

Calories per gram (or per volume) of a food. Low-density foods (vegetables, broths) help with fullness on fewer calories; high-density foods (nuts, oils, sweets) deliver more calories per bite.

A sugar alcohol about 70% as sweet as sucrose, providing 0.2 kcal/g. Mostly excreted unchanged in urine. A 2023 study linked high blood levels to elevated cardiovascular events; debate ongoing.

Nine amino acids the body cannot make and must obtain from food: leucine, isoleucine, valine, lysine, methionine, phenylalanine, threonine, tryptophan, histidine.

A 0 to 100 ranking of how quickly a carbohydrate-containing food raises blood glucose compared to pure glucose. Low GI ≤55, medium 56 to 69, high ≥70.

Combines GI with the actual carb amount in a serving: GL = (GI × grams of carbs) / 100. A more practical measure than GI alone. Low GL ≤10, medium 11 to 19, high ≥20.

A BMR estimation formula first published in 1919 and revised by Roza and Shizgal in 1984. Slightly less accurate than Mifflin-St Jeor for the modern adult population but still widely used. Men: 88.362 + 13.397 × kg + 4.799 × cm − 5.677 × age. Women: 447.593 + 9.247 × kg + 3.098 × cm − 4.330 × age.

The state of having enough fluid in the body. A common starting target is ~30 ml of total water per kg of body weight per day, including water from food.

A dangerous drop in blood sodium concentration, often caused by drinking too much plain water too fast (water intoxication). Documented in endurance athletes and people on strict water diets, generally above 6 L (200 oz) per day. Noakes 2003 (BJSM) describes cases in marathon runners. Symptoms: headache, nausea, confusion, seizures.

A pattern of cycling between eating and fasting periods. Common protocols: 16:8 (8-hour eating window), 18:6, 20:4, OMAD, 5:2, and eat-stop-eat. Effects on weight are similar to calorie restriction at matched calories per Patterson and Sears 2017.

A mineral required for oxygen transport in red blood cells (hemoglobin). RDA: 8 mg/day for adult men, 18 mg/day for women 19 to 50, 27 mg/day in pregnancy. Heme iron (animal sources) absorbs better than non-heme.

A BMR formula that uses lean body mass instead of total weight and gender. BMR = 370 + 21.6 × lean body mass (kg). More accurate than Mifflin or Harris-Benedict for athletes and very lean individuals who know their body fat percentage.

A very-low-carb (typically <50 g/day) high-fat diet that shifts the body to burning ketones for fuel. Used for weight loss, epilepsy treatment, and athletic experimentation.

A metabolic state where the body burns fat for fuel and produces ketone bodies (acetoacetate, beta-hydroxybutyrate, acetone) instead of glucose. Triggered by very-low-carb intake (under ~50 g/day) or prolonged fasting (typically 12 to 18+ hours). Mild ketosis often begins around 12 hours of fasting; deep ketosis after 18 to 24 hours.

An amino acid found in tea (especially matcha) that increases alpha brain waves and promotes calm focus. Often co-occurs with caffeine in tea, smoothing caffeine's edge.

Everything in the body that is not stored body fat: muscle, bone, organs, water, connective tissue. Often called "fat-free mass." Preserving lean mass during a cut is a major goal.

A branched-chain essential amino acid that triggers muscle protein synthesis via the mTOR pathway. The leucine threshold per meal is ~2.5 g for younger adults and ~3 g for adults over 50.

A nutrient the body needs in large amounts and uses for energy. The three macronutrients are protein (4 kcal/g), carbohydrates (4 kcal/g), and fat (9 kcal/g). Alcohol (7 kcal/g) sometimes counts as a fourth.

A mineral involved in 300+ enzymatic reactions, muscle relaxation, and sleep regulation. RDA: ~400 mg/day for adult men, 310 mg/day for adult women.

The calorie intake that holds your weight steady over time. Numerically equal to your TDEE for most adults. Used as the baseline for cuts and bulks.

An eating pattern based on traditional foods from countries bordering the Mediterranean: olive oil, fish, vegetables, whole grains, nuts, legumes, and moderate dairy. Consistently linked to lower cardiovascular risk.

A nutrient needed in small amounts (milligrams or micrograms per day). Includes vitamins and minerals. Deficiencies impair growth, immunity, and energy metabolism.

The most validated formula for estimating BMR in healthy adults. Men: 10 × kg + 6.25 × cm − 5 × age + 5. Women: 10 × kg + 6.25 × cm − 5 × age − 161. Published in the American Journal of Clinical Nutrition (1990).

A natural high-intensity sweetener from Siraitia grosvenorii fruit, 150 to 250× sweeter than sucrose. Zero calories, no glycemic impact. Often blended with erythritol.

Growth in the size of muscle fibers via increased contractile protein content. Driven by resistance training, adequate protein (≥1.6 g/kg/day), and a small calorie surplus.

The cellular process of building new muscle proteins. Stimulated by dietary protein (especially leucine) and resistance training. Targeting ~25 to 40 g protein per meal maximizes MPS for most adults.

Total carbohydrates minus fiber, and often minus sugar alcohols. Used by people tracking ketogenic or low-carb diets because fiber and most sugar alcohols have minimal impact on blood glucose.

An intermittent fasting protocol where all daily calories are eaten within a 1-hour window. Typically ~23 hours fasting per day. Aggressive and not recommended for everyone (women, lean athletes, people under 60 kg should consult a clinician first).

Protein Digestibility Corrected Amino Acid Score. The 1989 standard (capped at 1.0) used on FDA nutrition labels. Being replaced by DIAAS in scientific literature.

A plant protein isolated from yellow split peas. DIAAS around 0.65. Complete amino acid profile but lower in methionine; often blended with rice protein to balance.

An eating pattern centered on foods from plants: vegetables, fruits, legumes, whole grains, nuts, seeds, and oils. Ranges from vegan (no animal products) to flexitarian (mostly plants).

An electrolyte mineral that counterbalances sodium and supports blood pressure regulation. Adequate Intake: 3,400 mg/day for adult men, 2,600 mg/day for adult women.

A macronutrient providing 4 kcal per gram, made of 20 amino acids. Essential for muscle protein synthesis, immune function, enzymes, and hormones. The RDA is 0.8 g/kg/day; active adults often target 1.4 to 2.0 g/kg.

The average daily intake of a nutrient considered sufficient to meet the needs of 97 to 98% of healthy individuals at a given life stage and sex. Set by the U.S. National Academies (FNB).

Age-related loss of muscle mass and strength, typically starting in the 30s and accelerating after 60. Resistance training and higher protein intake (1.0 to 1.2 g/kg/day or more) help slow it.

The feeling of fullness and the absence of hunger after eating. High-protein, high-fiber, low-energy-density foods generally produce more satiety per calorie.

An electrolyte that regulates fluid balance and blood pressure. The FDA recommends ≤2,300 mg/day for adults; the AHA suggests an ideal of 1,500 mg/day. Excess sodium contributes to hypertension.

A natural sweetener derived from Stevia rebaudiana leaves, 200 to 350× sweeter than sucrose. Zero calories. The active glycosides (stevioside, rebaudioside A) are FDA-recognized as GRAS.

A chlorinated artificial sweetener about 600× sweeter than sucrose. Used in Splenda, many protein powders, and diet drinks. FDA-approved; not absorbed in significant amounts.

Calories burned digesting, absorbing, and metabolizing food. Protein has the highest TEF (20 to 30% of its calories), carbohydrates 5 to 10%, fats 0 to 3%. Roughly 10% of total daily expenditure for most diets.

Total calories burned per day: BMR + activity + digestion (thermic effect of food). Eating at TDEE maintains your weight. Eating below it loses weight; above it gains weight.

A water-soluble vitamin essential for red blood cell formation, neurological function, and DNA synthesis. RDA: 2.4 µg/day for adults. Found almost exclusively in animal foods; plant-based eaters often need supplementation.

A fat-soluble vitamin that regulates calcium absorption and bone health. Produced in skin from sunlight; also found in fatty fish and fortified dairy. RDA: 600 to 800 IU/day for most adults.

Fast-digesting milk protein (about 20% of total cow's-milk protein) absorbed within 60 to 90 minutes. DIAAS ~1.09. Highest leucine content of common protein powders.