Sports Nutrition

This deck is designed to build a solid foundation in the science of fueling athletic performance. It covers the three macronutrients in depth, exploring how carbohydrates, proteins, and fats each contribute to energy production, recovery, and overall health. You'll also work through key concepts like glycogen storage, nutrient timing, and the differences between simple and complex carbohydrates, as well as saturated and unsaturated fats. Together, these flashcards walk you through the basics every athlete or fitness enthusiast should understand.

The deck is well suited for athletes, coaches, personal trainers, sports science students, or anyone curious about how food choices affect training and competition. Whether you are preparing for an exam, planning your own nutrition strategy, or just wanting to separate fact from fad, the questions cover both foundational knowledge and more specific topics like BCAAs, omega-3s, and the anabolic window.

Because sports nutrition blends physiology with practical application, try to connect each card to a real-world scenario as you study. For example, when reviewing carbohydrate recommendations, think about how they would apply to a long run or a hard training session. Spacing your review sessions over several days works especially well here, since the material builds on itself and revisiting earlier concepts helps the newer ones stick. Consistent, short sessions will be more effective than cramming, leaving you with a confident grasp of how to fuel performance wisely.

The three macronutrients — protein, carbohydrates, and fats — form the foundation of any sports nutrition plan. Each provides energy at a different density: protein and carbohydrates yield approximately 4 kcal per gram, while fat delivers about 9 kcal per gram. A calorie (technically a kilocalorie) is a unit of energy representing the heat needed to raise the temperature of 1 kg of water by 1 °C. In nutrition, calories quantify both the energy content of food and the energy expenditure of physical activity, making them the basic currency of any diet plan.

Understanding total energy needs is the first step in designing an athlete's diet. Total Daily Energy Expenditure (TDEE) is calculated as Basal Metabolic Rate (BMR) multiplied by an activity factor. The Mifflin-St Jeor equation is the most accurate method for estimating BMR: for males, \( \text{BMR} = 10 \times \text{weight (kg)} + 6.25 \times \text{height (cm)} - 5 \times \text{age} - 5 \), and for females the same formula minus 161. Activity factors range from 1.2 for sedentary individuals to 1.9 for very active athletes. Once TDEE is known, athletes can determine whether they need a caloric surplus, deficit, or maintenance to match their training goals.

The thermic effect of food (TEF) also plays a role in energy balance, representing the energy required to digest, absorb, and process nutrients. Protein has the highest thermic effect at 20–30% of calories consumed, followed by carbohydrates at 5–10% and fat at 0–3%. TEF accounts for roughly 10% of total daily energy expenditure. The thermic effect of exercise (TEE), including both structured workouts and non-exercise activity thermogenesis (NEAT), is the most variable component of energy expenditure, ranging from 15–30% of TDEE depending on activity level.

Protein is essential for tissue repair, muscle growth, and immune function, with most sports nutrition guidelines recommending 1.2–2.0 g per kg of body weight per day for athletes. Endurance athletes typically need 1.2–1.4 g/kg to repair tissue and support immune function, while strength athletes require 1.6–2.2 g/kg to support muscle hypertrophy and recovery. Both groups benefit from distributing protein evenly across four to five meals throughout the day. Training status also affects needs: beginners can build muscle even in a slight deficit through body recomposition, intermediate athletes need a small surplus for muscle gain, and advanced athletes require very precise nutrition to continue progressing.

A complete protein contains all nine essential amino acids in adequate amounts: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Animal sources like meat, fish, eggs, and dairy are complete, as are soy and quinoa. The biological value (BV) of a protein measures the proportion of absorbed protein that is retained and used by the body, with whole egg as the reference at 100, whey protein at about 104, casein at 77, and soy at 74. The newer Digestible Indispensable Amino Acid Score (DIAAS) evaluates protein quality based on the digestibility of individual essential amino acids, with scores above 100 considered excellent. Plant proteins are generally lower in leucine and may have lower digestibility, but combining sources such as rice and pea protein creates a complete amino acid profile.

Branched-chain amino acids (BCAAs) — leucine, isoleucine, and valine — make up about 35% of muscle protein, with leucine serving as the primary trigger for the mTOR signaling pathway that activates muscle protein synthesis. Research suggests that 20–40 g of high-quality protein per meal is needed to maximally stimulate this response, with a leucine threshold of approximately 2.5–3 g per meal being key. Whey protein is a fast-digesting, complete protein derived from milk, available as concentrate (70–80% protein, containing some fat and lactose), isolate (90%+ protein with minimal fat and lactose, ideal for the lactose-intolerant), and hydrolysate (pre-digested for fastest absorption, most expensive). Casein, by contrast, is a slow-digesting milk protein that forms a gel in the stomach, providing sustained amino acid release over 6–8 hours, and is often recommended before bed to support overnight muscle protein synthesis.

Carbohydrates are the body's preferred fuel source during moderate-to-high intensity exercise. They are stored as glycogen in muscles (approximately 300–400 g) and the liver (about 75–100 g), providing readily available energy for athletic performance. Glycogen is the primary fuel for exercise above roughly 65% VO2max, and its depletion is a major cause of fatigue and reduced performance. The crossover concept in exercise metabolism describes how the body shifts from fat oxidation to carbohydrate oxidation as the primary fuel source as exercise intensity increases, with the crossover point typically occurring around 65% VO2max, varying with training status and diet. The Randle cycle (glucose-fatty acid cycle) similarly describes the competition between glucose and fatty acids for oxidation: when fat availability is high, fat oxidation increases and glucose oxidation decreases, and vice versa.

Carbohydrates are classified as simple or complex based on their chemical structure and digestion rate. Simple carbohydrates (monosaccharides and disaccharides) are quickly digested and raise blood sugar rapidly, as found in fruit, table sugar, and honey. Complex carbohydrates (polysaccharides) digest more slowly and provide sustained energy, with oats, rice, and potatoes being common examples. The glycemic index (GI) ranks carbohydrates on a scale of 0–100 based on how quickly they raise blood glucose: high GI foods (above 70) cause rapid spikes, while low GI foods (below 55) produce slower, sustained rises. Athletes should consume high GI foods during and immediately after exercise, when rapid glycogen replenishment and quick energy are most beneficial. Fiber, while important for gut health, blood sugar regulation, and satiety at 25–35 g per day, should be avoided 2–3 hours before exercise to prevent gastrointestinal discomfort.

Endurance athletes typically need 6–10 g of carbohydrate per kg of body weight per day, depending on training volume and intensity, with needs potentially exceeding 10 g/kg/day during ultra-endurance events. Carb loading is a strategy to maximize glycogen stores before endurance events lasting longer than 90 minutes, using 8–12 g of carbs per kg per day for 1–3 days before competition while tapering training, which can lead to glycogen supercompensation — loading muscles with 150–200% of normal glycogen levels. During exercise lasting longer than 60 minutes, athletes should consume 30–60 g of carbohydrates per hour from easily digestible sources such as sports drinks, gels, and bananas. For events longer than 2.5 hours, intake can increase to up to 90 g per hour by using a 2:1 glucose-to-fructose ratio, which utilizes two different intestinal transport pathways (SGLT1 and GLUT5) for greater absorption. Gut training — practicing race-day nutrition during training — can improve gastrointestinal tolerance and nutrient absorption over time.

Dietary fat plays several essential roles in athletic performance, providing essential fatty acids, supporting hormone production (including testosterone), aiding absorption of fat-soluble vitamins (A, D, E, and K), and serving as a fuel source during low-intensity and prolonged exercise. Athletes should consume 20–35% of total daily calories from fat, with intake below 20% potentially impairing hormone production and fat-soluble vitamin absorption. Emphasis should be placed on unsaturated fats over saturated ones for cardiovascular and overall health.

Saturated fats have no double bonds between carbon atoms and are typically solid at room temperature, with butter being a common example. Unsaturated fats have one or more double bonds and are usually liquid at room temperature, like olive oil. Among unsaturated fats, omega-3 fatty acids — particularly EPA and DHA — deserve special attention for athletes. Found in fatty fish, flaxseed, and walnuts, omega-3s reduce inflammation, support cardiovascular health, may improve recovery, and have been linked to reduced exercise-induced muscle soreness. Medium-chain triglycerides (MCTs) are fats with 6–12 carbon chains that are rapidly absorbed and transported directly to the liver for oxidation, providing quick energy; however, their ergogenic benefit is limited and they may cause gastrointestinal distress at effective doses.

A persistent myth is that eating fat makes you fat. This is false: fat gain results from a caloric surplus, regardless of macronutrient source. Dietary fat is essential for hormones, cell membranes, and vitamin absorption, and healthy fats from sources like avocados, nuts, and olive oil should comprise 20–35% of total calories. Similarly, the idea that carbohydrates eaten at night cause fat gain is unfounded — total daily calorie intake, not timing, determines fat gain or loss. Carbohydrates at night can actually improve sleep quality through their role in serotonin and melatonin production, which may be especially beneficial for athletes who train in the morning.

Once total daily energy expenditure is known, athletes manipulate calorie intake to match their training goals. A caloric surplus — consuming more calories than expended — is used for muscle gain, with a moderate surplus of 250–500 kcal per day above TDEE promoting muscle growth while minimizing fat accumulation. A caloric deficit — consuming fewer calories than expended — is necessary for fat loss, with a moderate deficit of 300–500 kcal per day below TDEE promoting fat loss while preserving muscle mass when combined with adequate protein and resistance training.

It is important to distinguish between weight loss and fat loss. Weight loss includes loss of fat, muscle, water, and glycogen, while fat loss specifically targets adipose tissue. To maximize fat loss while preserving muscle, athletes should maintain a moderate caloric deficit, keep protein intake high at 2.0+ g/kg, perform resistance training, and aim to lose 0.5–1% of body weight per week. However, as dieting progresses, the body undergoes metabolic adaptation (adaptive thermogenesis), reducing energy expenditure beyond what is predicted by weight loss alone. This includes decreased BMR, reduced NEAT, improved movement efficiency, and hormonal changes such as lower leptin and thyroid hormone levels, all of which make continued fat loss progressively harder.

Planned diet breaks and refeeds can help counteract these adaptations. Diet breaks are planned periods of 1–2 weeks of eating at maintenance calories during a fat loss phase, while refeeds are shorter 1–2 day periods of increased carbohydrate intake. Both may help restore leptin levels, reduce psychological stress, and mitigate metabolic slowdown. To calculate macronutrient ratios, athletes first determine calorie needs via TDEE, then set protein at 1.6–2.2 g/kg, fat at 20–35% of total calories, and fill the remaining calories with carbohydrates. For example, an 80 kg athlete needing 3000 kcal might consume 160 g protein (640 kcal), 83 g fat (750 kcal), and 403 g carbohydrates (1610 kcal). Periodized nutrition takes this further by adjusting calorie and macronutrient intake based on training phase: more carbohydrates during high-volume training, more protein during strength phases, and moderate intake during the off-season.

Hydration is critical for athletic performance, with general guidelines recommending at least 3–4 liters of water per day for active individuals, adjusted so that urine remains pale yellow. During exercise, athletes should aim for 400–800 mL per hour depending on sweat rate and environmental conditions. Even a 2% loss of body weight from fluid can impair performance by 10–20%. Signs of dehydration include dark yellow urine, thirst, dry mouth, headache, dizziness, fatigue, decreased performance, elevated heart rate, and reduced sweat rate.

Electrolytes — minerals that carry an electrical charge, including sodium, potassium, chloride, calcium, and magnesium — regulate fluid balance, nerve function, and muscle contraction. Athletes lose substantial electrolytes through sweat, particularly sodium at 500–1500 mg per liter of sweat. Sodium is the primary electrolyte lost in sweat and is essential for regulating fluid balance, nerve impulses, and muscle contractions. Hyponatremia — dangerously low blood sodium levels below 135 mmol/L — is often caused by drinking excessive water without adequate sodium replacement during prolonged exercise, and can cause nausea, confusion, seizures, and even death. Sports drinks containing water, 6–8% carbohydrates, and electrolytes are beneficial during exercise lasting longer than 60 minutes or in hot conditions; for shorter sessions, water is usually sufficient. Drinks can be classified as isotonic (matching blood osmolality, ideal for balanced replacement), hypotonic (faster fluid absorption with less energy), or hypertonic (more energy but slower absorption). Potassium works alongside sodium to regulate fluid balance and muscle contractions, with athletes needing 3500–4700 mg per day from foods like bananas, potatoes, and spinach.

Micronutrients — vitamins and minerals required in small amounts — do not provide energy but are critical for metabolism, immune function, bone health, and hundreds of enzymatic reactions. Iron is essential for hemoglobin and myoglobin, and deficiency impairs endurance performance and causes fatigue; the RDA is 8 mg for males and 18 mg for females, with female and endurance athletes at higher risk. Sports anemia (pseudoanemia) is a dilutional decrease in hemoglobin caused by expanded plasma volume in endurance athletes and is a normal adaptation rather than true anemia. Calcium supports bone health, muscle contraction, nerve signaling, and blood clotting, with athletes needing 1000–1300 mg per day. Vitamin D supports calcium absorption, bone health, immune function, and muscle function, with many athletes deficient, especially those training indoors; supplementation of 1000–2000 IU per day is often recommended. B vitamins serve as coenzymes in energy metabolism, magnesium is involved in over 300 enzymatic reactions including energy production and muscle contraction (with athletes potentially needing 400–600 mg per day), and zinc supports immune function, protein synthesis, and testosterone production. Antioxidants from whole foods neutralize free radicals produced during exercise, though excessive supplementation may blunt training adaptations because some oxidative stress is needed to signal adaptation.

Several supplements have strong evidence for enhancing athletic performance, with creatine monohydrate being one of the most studied and safest. Creatine is stored as phosphocreatine in muscles and regenerates ATP during short, high-intensity efforts, increasing muscle creatine stores by 20–40%. The standard protocol is a loading phase of 20 g per day (split into 4 doses) for 5–7 days, followed by a maintenance dose of 3–5 g per day, though simply taking 3–5 g per day without loading saturates muscles in about 28 days. Decades of research show no adverse effects on kidney or liver function in healthy individuals at recommended doses.

Caffeine reduces perceived exertion, increases alertness, and enhances endurance performance by 3–5%, with an effective dose of 3–6 mg per kg of body weight taken 30–60 minutes before exercise. Beta-alanine is an amino acid that increases intramuscular carnosine levels, buffering hydrogen ions during high-intensity exercise and reducing fatigue during efforts lasting 1–4 minutes; a common dose is 3–6 g per day, with the harmless tingling sensation (paresthesia) being a known side effect. Citrulline malate increases nitric oxide production and arginine levels, improving blood flow and reducing fatigue, with a typical dose of 6–8 g taken 30–60 minutes pre-exercise. Dietary nitrate from beetroot juice is converted to nitric oxide, which improves blood flow, reduces the oxygen cost of exercise, and enhances muscle efficiency, with an effective dose of about 6–8 mmol of nitrate taken 2–3 hours pre-exercise. Other useful supplements include HMB (a metabolite of leucine most effective for untrained individuals or during caloric restriction at 3 g per day), sodium bicarbonate as an extracellular buffer for efforts lasting 1–7 minutes at 0.2–0.3 g per kg taken 60–90 minutes pre-exercise, glutamine to support immune function in heavily training athletes, collagen peptides with vitamin C to support tendon and ligament health, and tart cherry juice to reduce muscle soreness and improve sleep. Pre-workout supplements typically combine caffeine, beta-alanine, citrulline, creatine, and nitric oxide precursors.

Nutrient timing involves strategically consuming specific nutrients at specific times relative to exercise to optimize performance, recovery, and body composition. The pre-workout meal, eaten 2–4 hours before exercise, should contain moderate protein (20–40 g), complex carbohydrates for sustained energy, and low-to-moderate fat. The post-workout meal should include 20–40 g of protein to stimulate muscle protein synthesis and 0.8–1.2 g of carbohydrates per kg to replenish glycogen stores, generally within 2 hours after exercise. The so-called anabolic window — a supposed 30–60 minute post-exercise period of enhanced nutrient uptake — is now understood to be wider than originally thought, with total daily protein intake being more important than precise timing. Sleep is also a critical component of recovery, as growth hormone is primarily released during deep sleep, facilitating muscle repair; a casein protein shake before bed can provide sustained amino acids during sleep.

Certain populations require specific nutritional considerations. The Female Athlete Triad consists of three interrelated conditions: low energy availability (with or without disordered eating), menstrual dysfunction (amenorrhea), and low bone mineral density (osteoporosis). This is now part of the broader concept of Relative Energy Deficiency in Sport (RED-S), which describes impaired physiological function caused by low energy availability affecting both males and females, with impacts on metabolism, menstrual function, bone health, immunity, protein synthesis, cardiovascular health, and psychological well-being. Masters athletes (over 40) need higher protein intake (1.6–2.2 g/kg/day) due to anabolic resistance, along with adequate vitamin D, calcium, omega-3s, and possibly creatine supplementation, with longer recovery times making post-workout nutrition timing more important.

Athletes in weight-class sports should minimize weight-cutting and compete as close to their natural weight as possible; if cutting is necessary, weight should be lost gradually at 0.5–1 kg per week, with high protein intake maintained and moderate water and sodium manipulation in the final days. Team sports like soccer and basketball require 5–7 g of carbs per kg per day and 1.4–1.7 g of protein per kg per day, with emphasis on pre-game carb loading, halftime refueling, and post-game recovery nutrition within 2 hours. Swimmers need high carbohydrate intake (6–10 g/kg/day) due to high training volumes and benefit from antioxidant-rich foods to combat the oxidative stress from pool chlorine. Marathon nutrition involves carb loading at 8–12 g/kg for 2–3 days pre-race, a familiar pre-race meal 3–4 hours before, consuming 30–60 g of carbs per hour during the race, and aggressive post-race recovery with protein, carbs, and electrolytes.

Several common nutrition myths deserve clarification. The claim that you must eat every 2–3 hours to boost metabolism is largely a myth: meal frequency has minimal impact on metabolic rate when total calorie and protein intake are equated, and the thermic effect of food depends on total intake rather than frequency. Detoxing and cleansing are unnecessary because the liver, kidneys, and digestive system already detoxify the body effectively; juice cleanses often lack protein and calories and can impair performance and recovery. Intermittent fasting can aid fat loss but may impair performance and muscle gain if total calorie and protein intake are insufficient or if training occurs in fasted states. The ketogenic diet, a very low-carb, high-fat approach forcing the body to use fat and ketones as primary fuel, may benefit ultra-endurance athletes but generally impairs high-intensity performance due to reduced glycogen availability. Alcohol impairs muscle protein synthesis, dehydrates the body, disrupts sleep, reduces glycogen resynthesis, impairs reaction time, and increases injury risk, with even moderate post-exercise consumption significantly hindering recovery. Finally, supplements are not required to build muscle — a well-planned diet can provide all necessary nutrients — though creatine, protein powder, and vitamin D may be convenient and beneficial when dietary intake is insufficient.