Plain definitions for how you eat, train, and recover
Quick, practical explanations for the nutrition, training, and recovery terms you run into across Fuel. Look up a macro, a GLP-1, a supplement, a metabolic marker, or a coaching concept while you log meals, tune targets, or work through an insight that mentions something new.
Macronutrients
Macronutrients are protein, carbohydrate, and fat, the nutrients that provide nearly all of the energy in your diet and drive most day to day nutrition decisions.
4-4-9 Rule Nutrition
The 4-4-9 rule is the standard calorie conversion framework used in nutrition planning.
Carbohydrate Sources
Carbs differ most in fiber density and digestion speed.
Casein
Casein is the slower-digesting protein fraction in milk.
Cholesterol
Cholesterol is a biological substrate for hormone and membrane function, and blood levels reflect diet, genetics, and training context..
Complex Carbs
Complex carbs pair fiber, starch, and slower digestion in a way that makes them useful for most normal meals.
Dietary Fat
Dietary fat supports satiety, hormone synthesis, and training consistency when placed in the right range for your phase.
Fiber Intake
Fiber supports digestion, satiety, and blood pattern stability.
Insoluble Fiber
Insoluble fiber is the fraction of plant carbohydrate that does not dissolve in water and contributes most strongly to stool bulk and intestinal transit.
Leucine
Leucine is an essential branched-chain amino acid that helps turn a protein-containing meal into a strong muscle protein synthesis signal..
Omega-3 Fatty Acids
Omega-3s include EPA and DHA from marine foods and ALA from plants, with different conversion efficiencies and physiological roles..
Protein Quality
Protein Quality describes how complete and bioavailable a protein source is for tissue repair and immune support.
Resistant Starch
Resistant starch is starch that escapes digestion in the small intestine and reaches the colon, where gut microbes can ferment part of it into short-chain fatty acids.
Saturated Fat
Saturated Fat affects cardiovascular risk markers, but the magnitude and direction depend on the type of saturated fatty acid, the food matrix it sits in, what it replaces in the diet, and individual metabolic context.
Simple Carbs
Simple carbs digest quickly and can raise blood sugar faster than complex carbs.
Soluble Fiber
Soluble fiber is the fraction of carbohydrate that dissolves or swells in water and changes how food behaves in the gut.
Trans Fat
Trans fat is the fat subtype with the clearest case for elimination because even small intakes worsen blood lipids and raise cardiovascular risk.
Unsaturated Fat
Unsaturated Fat includes monounsaturated and polyunsaturated fats, with Saturated Fat tracked separately..
Whey Protein
Whey protein is the fast-digesting protein fraction of milk left after cheese production.
Bioelectrical Impedance Analysis
Bioelectrical impedance analysis, usually shortened to BIA, is the method used by most smart scales and many in-clinic body composition devices to estimate body fat, fat-free mass, and total body water..
Body Composition
Body composition describes how much of your body weight comes from fat mass versus fat-free mass, which includes muscle, organs, bone, and water.
Body Fat Percentage
Body fat percentage estimates how much of your total body weight is fat tissue.
Body Recomposition
Body recomposition means reducing fat mass while maintaining or gaining muscle mass at the same time.
DEXA Scan
A DEXA scan uses two X-ray energies to estimate fat mass, lean mass, bone mineral content, and regional distribution across the body.
Fat-Free Mass
Fat-Free Mass includes everything in the body that is not fat: muscle, organs, bone, water, glycogen, and connective tissue.
Lean Mass
Lean Mass is the non-fat fraction that is responsive to nutrition, hydration, inflammation, and training.
Rate-of-Gain Guardrails
Rate-of-gain guardrails are the weekly weight, waist, and training-output bands that keep a calorie surplus productive.
Sarcopenia
Sarcopenia is the age-related loss of muscle strength and muscle quantity, with the strength loss now treated as the key first signal.
Skinfold Calipers
Skinfold calipers measure the thickness of a pinched fold of skin and subcutaneous fat, then use either the raw sum of sites or a prediction equation to estimate body fat percentage.
Waist Circumference
Waist circumference is the tape-measure distance around the abdomen at a standardized anatomical site.
Active Calories
Active Calories are the calories a device attributes to movement above rest.
Adaptive Calorie Targets
Adaptive calorie targets are calorie prescriptions that update over time based on real behavioral and physiological data rather than remaining fixed at the number a formula produced during onboarding.
Basal Metabolic Rate
Basal Metabolic Rate is the minimum energy your body would use under tightly controlled resting conditions.
Calorie Burn Estimation
Calorie burn estimation is the process of estimating how much energy you burn from baseline metabolism, daily movement, and structured exercise, then checking whether those estimates match what your body weight and intake trend are actually doing..
Ghrelin
Ghrelin is a stomach-derived hormone that increases hunger when your body expects food or senses an energy shortfall.
Insulin
Insulin is the peptide hormone released by pancreatic beta cells that helps move glucose out of the bloodstream and into muscle, liver, and fat tissue.
Insulin Resistance
Insulin resistance often builds quietly.
Insulin Sensitivity
Insulin sensitivity determines how effectively your cells respond to insulin's signal to take up glucose from your bloodstream.
Leptin
Leptin is a hormone released by fat tissue that tells the brain how much stored energy is available.
NEAT
Non-Exercise Activity Thermogenesis (NEAT) is energy from daily movement outside planned workouts.
Resting Metabolic Rate
Resting Metabolic Rate is the energy you burn at rest while awake in a relaxed state.
Testosterone
Testosterone is an androgen hormone that helps regulate muscle maintenance, libido, mood, red blood cell production, bone health, and training recovery.
Thermic Effect of Food
Thermic effect of food is the energy your body spends digesting, absorbing, transporting, and storing nutrients after a meal.
Thyroid Function
Thyroid function is the output of the thyroid-pituitary axis that controls how much thyroxine (T4) and triiodothyronine (T3) reach the body’s tissues.
Total Daily Energy Expenditure
Total Daily Energy Expenditure (TDEE) is the sum of calories you burn each day.
Appetite Suppression
Appetite suppression lowers hunger, interest in food, or expected meal size.
Calorie Deficit
A calorie deficit occurs when intake is lower than daily expenditure, which creates weight loss over time.
Calorie Surplus
A calorie surplus supports tissue gain only when excess is controlled.
Diet Fatigue
Diet fatigue is the cumulative strain that builds when a fat-loss phase runs long enough for hunger, food focus, low energy, and declining adherence to start changing the quality of the plan.
Food Noise
Food noise is the persistent background pull of food-related thoughts, urges, and attention shifts between meals.
GLP-1
GLP-1 (glucagon-like peptide-1) is a hormone your gut produces after eating to regulate hunger and blood sugar.
GLP-1 Receptor Agonist
A GLP-1 receptor agonist is a prescription medication that mimics the GLP-1 hormone your gut produces after eating.
Liraglutide
Liraglutide is a GLP-1 receptor agonist that reduces appetite and helps stabilize blood sugar through daily injections.
Maintenance Calories
Maintenance Calories are the intake that keeps body weight stable over time.
Metabolic Adaptation
A calorie deficit that worked in week two can shrink by week ten as body mass drops, daily movement slips, and energy expenditure falls.
Mounjaro
Mounjaro is a weekly tirzepatide injection approved for type 2 diabetes, where weight loss occurs as a secondary effect.
Ozempic
Ozempic is a weekly semaglutide injection approved for type 2 diabetes, where weight loss occurs as a secondary effect.
Retatrutide
Retatrutide is an investigational triple-receptor agonist (GLP-1, GIP, and glucagon) currently in Phase 3 clinical trials (TRIUMPH program).
Reverse Dieting
Reverse dieting is a staged increase in intake after a deficit so training quality and hunger stabilize while weight regain stays controlled.
Rybelsus
Rybelsus is the daily oral tablet form of semaglutide, approved for type 2 diabetes.
Satiety
Satiety is the reduction in hunger after a meal that delays the next eating episode.
Saxenda
Saxenda is a daily liraglutide injection approved for chronic weight management.
Semaglutide
Semaglutide is a GLP-1 receptor agonist that reduces appetite and stabilizes blood sugar by mimicking the GLP-1 hormone your gut produces after eating.
Tirzepatide
Tirzepatide is a dual GIP/GLP-1 receptor agonist that activates two hormone pathways involved in appetite regulation and blood sugar control.
Victoza
Victoza is a daily liraglutide injection approved for type 2 diabetes, where appetite reduction and weight loss occur as secondary effects.
Wegovy
Wegovy is a weekly semaglutide injection approved for chronic weight management.
Weight Loss Plateau
A weight loss plateau is a 2+ week period with no downward trend despite consistent effort..
Zepbound
Zepbound is a weekly tirzepatide injection approved for chronic weight management.
Altitude Nutrition
Altitude nutrition is the food, fluid, and micronutrient plan that supports performance and recovery when you train, travel, or compete in thinner air.
Beta-Alanine
Beta-alanine is an amino acid used to raise muscle carnosine, a compound that helps buffer the acid load that builds during very hard work.
Caffeine
Caffeine is a central nervous system stimulant that blocks adenosine receptors, which can lower perceived effort, raise alertness, and improve endurance or repeated high-intensity output when the dose matches the task.
Collagen
Collagen is the main structural protein in tendons, ligaments, cartilage, bone, and skin.
Creatine
Creatine is a compound stored mainly in skeletal muscle that helps you regenerate ATP during short, hard efforts.
Creatine Loading
Creatine loading is a short high-dose phase, usually 20 grams per day split into four 5 gram servings for 5 to 7 days, used to raise muscle creatine stores quickly before moving to a maintenance dose.
Deload Week
A Deload Week reduces training stress for a short block so fatigue can fall faster than fitness.
Glycogen
Glycogen is the storage form of carbohydrate in muscle and liver, and it helps decide how much hard work you can support before pace, power, and concentration drop.
Glycogen Loading
Glycogen loading is a short-term high-carbohydrate strategy used before long endurance events to raise stored carbohydrate in muscle before the start.
Gut Training
Many endurance athletes know their fueling targets on paper and still fail to absorb them when pace, heat, and stress rise.
Heart Rate Zones
Heart rate zones group intensity into bands so cardio sessions are repeatable and fatigue is easier to manage..
Interval Training
Interval training alternates focused work and recovery blocks to build fitness efficiently without turning every session into a grind..
Lactate Threshold
Lactate threshold is the exercise intensity where blood lactate starts rising faster than it can stay stable during continued work.
Low Energy Availability
Low energy availability happens when dietary intake does not cover both exercise cost and the body’s remaining physiological work.
Menstrual Cycle Nutrition
Menstrual cycle nutrition is the use of cycle data to guide food, fluid, and training support across the month.
Muscle Protein Synthesis
Muscle protein synthesis, often shortened to MPS, is the process of building new muscle proteins after training and protein feeding.
Periodized Nutrition
Periodized nutrition changes energy, carbohydrate, fluid, and protein distribution across a training week so each session starts with the fuel profile that fits its purpose.
Post-Workout Nutrition
Post‑Workout Nutrition supports repair and glycogen replenishment, especially when paired with Pre-Workout Nutrition.
Pre-Workout Nutrition
Pre-workout nutrition fuels performance while avoiding digestive discomfort during training.
Progressive Overload
Progressive overload increases training stress gradually to drive adaptation, while recovery sets the pace of progress..
Recovery Time
Recovery time is how long your body needs before repeating hard work at the same intensity and quality..
Training Split
A training split organizes sessions across the week so volume, intensity, and recovery are distributed on purpose..
VO2 Max
VO2 max is the highest rate at which your body can take in, transport, and use oxygen during intense exercise.
Electrolyte Balance
Electrolyte Balance supports nerve signaling, muscle contraction, and fluid distribution.
Hydration
Hydration supports blood volume, temperature control, and performance.
Hyponatremia
Hyponatremia means blood sodium concentration has fallen too low, usually below 135 mmol/L.
Sodium Intake
Sodium supports fluid balance, nerve communication, and exercise performance.
Sodium Loading
Sodium loading is a short pre-race strategy that combines extra sodium with planned fluid intake to help the body retain more of what you drink before a long event.
Sports Drink
Long endurance sessions create a double demand.
Sweat Rate
Sweat rate is the amount of body fluid you lose per hour during exercise, usually expressed in liters per hour.
Water Intake Goals
Water Intake Goals provide a structured framework for matching fluid intake to daily needs and training demands.
B Vitamins
B Vitamins function as coenzymes across energy conversion, methylation, and redox control.
Calcium Intake
Calcium acts as both a structural mineral and a signaling mineral.
Iodine
Iodine is the trace mineral your thyroid uses to make T4 and T3, so an intake gap can lower thyroid hormone output, alter resting metabolic rate, and eventually show up as fatigue, cold intolerance, constipation, or goiter.
Iron Levels
Iron status affects oxygen transport and can influence energy, endurance, and training recovery.
Magnesium
Magnesium supports neuromuscular, energy, and recovery systems through multiple cellular roles.
Micronutrients
Micronutrients are nutrients required in small absolute quantities but essential for metabolic continuity, cellular signaling, and recovery.
Potassium
Potassium helps maintain fluid balance and supports muscle and nerve function, working with sodium intake as part of overall electrolyte balance..
Supplements
Supplements can be useful when food intake, schedule variability, and recovery demands create persistent gaps in key nutrients.
Vitamin D
Vitamin D is both hormone precursor and signaling regulator.
Zinc
Zinc is a trace mineral that helps regulate immune defense, wound repair, protein synthesis, and taste and smell, so low intake can show up as poor recovery, frequent illness, or skin and appetite changes long before a lab result is checked.
Anabolic Resistance
Anabolic resistance is the reduced muscle protein synthesis response to a dose of protein or resistance exercise that would produce a stronger signal in a younger, healthier, or better-fed state.
Balanced Diet
A balanced diet is a repeatable way of eating that gives you enough protein, carbs, fats, fiber, and micronutrients to match your energy needs and support health, recovery, and performance.
Carb Cycling
Carb Cycling places carbohydrate load around demands while preserving weekly energy alignment..
Competition Prep Nutrition
Competition prep nutrition is the nutrition strategy used in the final stretch before a physique or weight-class competition, when the goal is to lower body fat percentage without arriving flat, exhausted, or visibly smaller from lost lean mass.
Diet Break
A diet break is a planned return to maintenance calories for several days or about one to two weeks during a fat-loss phase.
Fermented Foods
Fermented foods are foods that microbes change through controlled microbial growth or enzymatic activity, which shifts flavor, texture, shelf life, and often the live-microbe profile of the final food.
Flexible Dieting
Flexible dieting gets sold as permission to eat anything if the macros match.
Glycemic Index
Glycemic Index ranks carbohydrate foods by how quickly they raise blood glucose under standardized testing conditions.
Glycemic Load
Glycemic Load combines carbohydrate quality and portion size into one planning number.
Gut Microbiome
The gut microbiome is the collection of bacteria, archaea, viruses, and fungi living mainly in your large intestine.
High-Protein Diet
A high-protein diet raises daily protein intake high enough to change hunger, recovery, and body-composition outcomes.
Intermittent Fasting
Intermittent fasting is a timing framework for energy intake, not a stand-alone recovery or fat-loss shortcut.
Ketogenic Diet
A ketogenic diet is a very low-carbohydrate, high-fat eating pattern designed to produce nutritional ketosis.
Meal Replacement
Meal replacements work as a practical fallback when cooking time is constrained.
Mediterranean Diet
A Mediterranean diet is a food pattern centered on vegetables, fruit, legumes, whole grains, extra-virgin olive oil, nuts, seafood, and regular home-style meals.
Menopause Nutrition
Menopause nutrition is the way you structure food intake when falling ovarian estrogen starts shifting bone turnover, muscle retention, and fat distribution.
Nutrient Density
Nutrient Density describes how much vitamin, mineral, fiber, and protein value a food gives you for the calories it costs.
Nutrient Timing
Nutrient Timing schedules meals around activity so performance, recovery, and appetite work with the training plan instead of against it.
Plant-Based Diet
A plant-based diet is a food pattern where most meals are built from legumes, whole grains, vegetables, fruit, nuts, seeds, and plant oils.
Postpartum Nutrition
Postpartum nutrition starts with overlap.
Pre-Sleep Protein
Pre-sleep protein refers to consuming a protein-rich meal or supplement in the 30 to 60 minutes before going to bed.
Prebiotics
Prebiotics are fermentable food components that feed resident gut microbes and change how a meal behaves after you eat it.
Pregnancy Nutrition
The nutrition gaps with the biggest developmental consequences open early, often before appetite, body weight, or even pregnancy awareness catch up.
Probiotics
Probiotics are live microorganisms used for a specific health outcome, usually in a food or supplement product.
Protein Distribution
Protein distribution refers to how you spread your total daily protein intake across individual meals and snacks throughout the day.
Protein Timing
Protein timing is how you spread protein across the day to support recovery and muscle growth.
Refeed Day
A refeed day temporarily raises calories (often via carbs) during fat loss to support training and adherence..
Satiety Index
The satiety index ranks foods by how filling they are per calorie.
Short-Chain Fatty Acids
Short-chain fatty acids are small molecules made mainly in the colon when gut microbes ferment fiber and other non-digestible carbohydrates.
Ultra-Processed Foods
Ultra-processed foods are industrial formulations made mostly from refined substances extracted from foods, plus additives used to change taste, texture, shelf life, and convenience.
Bulk Cooking
Bulk Cooking means making several servings of core foods in one session so your week runs on prepared building blocks instead of daily improvisation.
Grocery List
A Grocery List is a planning tool, not a random basket, so each buy cycle should align with training phase and expected prep rhythm..
Macro-Friendly Recipes
Macro-Friendly Recipes provide predictable per-serving values so you can hit targets with less guesswork.
Meal Frequency
Meal frequency is a scheduling lever for consistent protein and energy distribution.
Meal Planning
Meal Planning maps your targets to meals you will actually eat..
Meal Prep
Meal Prep turns meal planning into a controlled execution loop with fewer daily choices..
Meal Prep Containers
Meal Prep Containers make a meal-prep system repeatable by fixing portion size, storage order, and grab-and-go friction before the week gets busy.
Meal Suggestions
Meal Suggestions combine remaining macros, timing, and schedule reality so the next meal is practical instead of theoretically perfect.
Portion Control
Portion Control keeps meals aligned with your targets without weighing every ingredient.
Serving Sizes
A serving size is the reference amount on a label or database entry, not a command about how much you should eat.
Barcode Scanning
Barcode Scanning pulls packaged food data into your log quickly, which is why it saves time.
Calorie Counting Accuracy
Calorie counting accuracy is the degree to which a person's logged food intake reflects their actual energy consumption.
Food Database
A food database stores nutrition entries for quick search and logging.
Food Diary
Food Diary records what you eat and drink alongside the context that explains why the intake happened.
Food Logging
Food logging gives measurable data for energy and behavior, while the method stays simple enough to sustain.
Food Scales
Food scales improve portion accuracy when visual estimates stop being trustworthy.
Macro Tracking
Macro Tracking turns food entries into multi-week trend data that reveals structural patterns in how you eat.
Photo Logging
Photo logging is a fast way to capture what you ate when full text entry would slow you down or make you skip the log entirely.
Voice Logging
Voice logging captures meals by speech for speed, then converts them into structured food entries.
Adaptive Calorie Goals
Adaptive Calorie Goals are calorie targets that change when the evidence changes.
Calorie Targets
Calorie Targets convert a maintenance estimate into a daily intake range that matches the job you are trying to do.
Macro Budget
A Macro Budget is a practical spending plan for protein, carbohydrate, and fat across the week, not just a single-day target sheet.
Macro Ratios
Macro ratios describe how your calories split between the three macronutrients, protein, carbs, and fat.
Macro Suggestions
Macro Suggestions are context-based adjustments to your day-level macro plan, not a fixed template.
Macronutrient Profile
A macronutrient profile shows how your daily calories split across the three macronutrients, protein, carbs, and fat.
Macros by Meal
Macros by meal distribute your daily targets across meal slots so totals stay steady even on busy days.
Personalized Macro Targets
Personalized Macro Targets size protein, carbohydrate, and fat around your goal, body size, training load, and schedule.
Blood Sugar Control
Blood sugar control means keeping glucose response stable enough that you are not spending the day bouncing between sharp spikes, crashes, cravings, and fatigue.
Bone Mineral Density
Bone mineral density, usually shortened to BMD, is the amount of mineral measured in a given area of bone, most often by DEXA scan and usually reported in g/cm².
CGM
A continuous glucose monitor (CGM) is a small wearable device that tracks your glucose levels around the clock, offering a window into how your body responds to everything from your morning coffee to your evening workout.
Ferritin
Ferritin is the main blood marker used to estimate stored iron.
Omega-3 Index
The Omega-3 Index is the percentage of EPA and DHA in red blood cell membranes.
Step Count
Step Count tracks daily movement and gives a practical signal for non-exercise activity, but the number only matters when it is interpreted in context.
Wearable Calorie Accuracy
Wearable devices have become the primary way people estimate how many calories they burn in a day.
Wearable Metrics
Wearable metrics capture activity and recovery data that inform daily plans.
Ashwagandha
Ashwagandha is an herbal supplement from Withania somnifera that is usually sold for stress, anxiety, sleep, or hormone support.
Binge Eating Patterns
Binge eating patterns are recurrent episodes of eating that feel difficult to stop and usually end with distress, secrecy, or a push to compensate later.
Cortisol
Cortisol is a glucocorticoid hormone released by the adrenal glands that helps manage wakefulness, blood sugar availability, immune signaling, and fuel use during stress.
Melatonin
Melatonin is a hormone released mainly by the pineal gland in darkness that signals biological night to the brain and body.
Mindful Eating
Mindful Eating means paying attention to hunger, appetite, pace, and satisfaction while the meal is actually happening.
Self-Monitoring Effect
The self-monitoring effect is the phenomenon where the act of observing and recording your own behavior changes that behavior.
Sleep Hygiene
Sleep hygiene is the set of behaviors and environment choices that make solid sleep more likely..
Sleep Tracking
Sleep tracking records duration and quality signals so recovery plans are based on trends, not single-night noise..
Stress Management
Stress management reduces mental and physical strain so recovery and decision quality improve.
Food Allergy Tracking
Food Allergy Tracking records what you ate, when symptoms started, how severe they became, and what else was happening around the event.
Food Intolerance
Food intolerance is a dose-dependent digestive response caused by enzymatic deficiency, transport limitation, or chemical sensitivity.
Gluten Sensitivity
Many users report symptoms after gluten exposure, but the underlying cause is often not one pattern.
Lactose Intolerance
Lactose Intolerance is a digestion limit, and tolerance is often tied to total dose and timing..
Low FODMAP Diet
A low FODMAP diet is a structured elimination and reintroduction protocol that lowers fermentable oligosaccharides, disaccharides, monosaccharides, and polyols for a short period to reduce IBS-type symptoms and identify personal trigger thresholds, because fermentable carbohydrates can drive bloating, pain, gas, stool urgency, and race-day gut instability in people with a sensitive gut.
Plant-Based Proteins
A plant-based diet can meet intake goals when plant-based proteins are chosen and combined intentionally.
Adaptive Calorie Algorithms
Every nutrition app starts by assigning you a calorie target.
Adaptive Learning
Adaptive Learning updates recommendations as new behavior, recovery, and outcome data arrive.
AI Coach
AI Coach is a coaching layer that uses your logs, targets, and trends to help with habits, calories, and macro execution.
AI Diet Planning
AI Diet Planning turns a calorie target, macro structure, schedule, preferences, and practical limits into a repeatable eating plan.
AI Food Photo Accuracy
AI food photo recognition has become the default way millions of people log meals.
AI for Nutrition Coaches
Nutrition coaching has always been limited by a fundamental constraint: a human coach has a fixed number of hours per week and a finite capacity for detailed data review.
AI Recipe Generator
An AI Recipe Generator creates meal ideas that fit your targets, constraints, and kitchen reality without forcing you to start from a blank screen each time.
AI vs Human Coaching
The question of whether AI can replace human nutrition coaches is the wrong question.
Chatbot Feedback
Chatbot Feedback handles adherence, appetite, and stress questions with scenario logic and explicit confidence tags.
Progress Visualization
Progress Visualization turns logs into trend views that make decisions easier.
Trend Analysis
Trend analysis smooths noisy data so changes are based on patterns, not single days.
Heat Shock Proteins
Heat shock proteins (HSPs) are a family of intracellular chaperones that rise when cells face temperature, oxidative, or mechanical stress.
Passive Heat Therapy
Passive heat therapy refers to repeated exposure to an external heat source without exercise, used to raise core temperature on a defined schedule.
Sauna Safety and Contraindications
Sauna safety is the set of conditions, medications, and life stages where the cardiovascular and thermal load of heat exposure carries enough risk that the right answer is to defer, modify, or get a clinician in the loop.
