Sports nutrition is the practice of tailoring what, when, and how much you eat and drink to support physical training, recovery, and performance. It goes beyond general healthy eating by matching your calorie and nutrient intake to the specific demands of your sport, your training volume, and your body composition goals. Whether you’re a recreational runner or a competitive powerlifter, the core principles are the same: fuel your activity, repair your tissues, and keep your body’s systems functioning well under stress.
Energy Balance: The Foundation
The single most important principle in sports nutrition is consuming enough total calories to offset what you burn during training. This concept, called energy availability, determines whether your body has the resources to build muscle, maintain bone density, support your immune system, and regulate hormones. When calorie intake consistently falls short of exercise demands, the consequences go well beyond feeling tired. Chronic under-fueling, now formally recognized as Relative Energy Deficiency in Sport (RED-S), can suppress reproductive hormones, disrupt menstrual cycles, raise stress hormone levels, lower thyroid function, weaken bones, and reduce neuromuscular performance.
RED-S isn’t limited to eating disorders or extreme dieting. It often happens when athletes simply don’t adjust their food intake to match increased training loads. One marker clinicians use is comparing your measured resting metabolic rate to your predicted rate. A ratio below 0.90 suggests your body has downshifted its metabolism to conserve energy, a clear sign you’re not eating enough.
Carbohydrates: Your Primary Fuel Source
Carbohydrates power both endurance and strength training. Your muscles and liver store carbohydrates as glycogen, and those stores are the primary fuel source during moderate-to-high intensity exercise. When glycogen runs low, performance drops sharply.
How many carbohydrates you need depends on training volume. For general training, the recommended range is 5 to 7 grams per kilogram of body weight per day. Endurance athletes doing two to three hours of intense daily training need 7 to 12 grams per kilogram. For a 70-kilogram (154-pound) athlete, that general range translates to roughly 350 to 490 grams of carbohydrates daily, or 490 to 840 grams at the high end for heavy endurance work. Those numbers are significantly higher than what most people eat, which is why athletes often need deliberate meal planning to hit their targets.
Protein: Muscle Repair and Growth
Protein provides the building blocks your body uses to repair exercise-damaged muscle fibers and build new tissue. The International Society of Sports Nutrition recommends 1.4 to 2.0 grams of protein per kilogram of body weight per day for most exercising individuals. Strength athletes aiming to build muscle tend to need the higher end of that range, around 1.6 to 2.2 grams per kilogram. Endurance athletes typically need 1.2 to 2.0 grams per kilogram.
If you’re trying to lose body fat while preserving muscle, protein needs climb even higher, to 2.3 to 3.1 grams per kilogram per day. This helps protect lean mass when calories are restricted.
Distribution throughout the day matters too. Each meal or snack should deliver roughly 20 to 40 grams of high-quality protein (from sources like eggs, dairy, meat, fish, or soy) to maximally stimulate muscle repair. In younger adults, even 20 to 30 grams per serving appears sufficient. The key amino acid driving this process is leucine, and you need about 1 to 3 grams of it per protein dose, an amount naturally present in most animal proteins and some plant sources like soy.
Fat: Essential but Often Overlooked
Dietary fat supports hormone production, joint health, and the absorption of fat-soluble vitamins. The general recommendation for athletes is 20 to 35 percent of total calorie intake, with saturated fat kept below 10 percent. Unlike carbohydrates and protein, fat recommendations don’t shift dramatically between sports. Most strength and power athletes don’t need to modify their fat intake in any special way. The main risk is cutting fat too low (below 20 percent of calories), which can interfere with hormone levels and overall health.
Nutrient Timing: What the Evidence Shows
The idea of a narrow “anabolic window” after exercise, where you must eat protein within 30 minutes or lose your gains, has been a staple of gym culture for decades. The current evidence is more nuanced. If you ate a substantial meal one to two hours before training, that meal’s digestion continues well into the recovery period, effectively serving as both your pre- and post-workout nutrition. In that scenario, rushing to consume a protein shake immediately after isn’t necessary.
The timing does matter more when you train in a fasted state or haven’t eaten in three to four hours. In that case, consuming at least 25 grams of protein as soon as possible after training helps reverse muscle breakdown and kickstart recovery. A practical guideline: aim for 0.4 to 0.5 grams of protein per kilogram of lean body mass in both your pre- and post-exercise meals, and don’t let those meals be separated by more than about three to four hours (accounting for the workout itself). If those meals are large mixed meals with plenty of calories, you can stretch that gap to five or six hours.
Hydration and Electrolytes
Losing just 2 percent of your body weight in fluid is enough to measurably impair both physical performance and cognitive function, and the effects worsen as dehydration deepens. For a 70-kilogram athlete, that’s only 1.4 kilograms (about 3 pounds) of sweat loss. During intense exercise in warm conditions, many athletes exceed that threshold within an hour.
The most reliable way to track your hydration is by weighing yourself before and after training. After exercise, the goal is to replace 150 percent of the fluid you lost. If you dropped 1 kilogram during a session, you’d drink 1.5 liters in the hours afterward. The extra 50 percent accounts for continued sweat and urine losses during recovery.
Sodium is the primary electrolyte lost in sweat, and the amount varies enormously between individuals. Whole-body sweat sodium concentration ranges from 10 to 70 millimoles per liter, meaning some athletes lose several times more sodium than others during the same workout. Rather than trying to calculate exact replacement numbers, most sports nutrition guidelines recommend categorizing yourself as a low, moderate, or heavy sweater (based on sweat marks on clothing, taste of sweat, and post-exercise weight changes) and choosing a corresponding replacement strategy with electrolyte drinks or salted foods.
Micronutrients That Matter Most
Two micronutrient deficiencies are especially common in athletes and directly affect performance: iron and vitamin D.
Iron carries oxygen in your blood and is critical for endurance capacity. Athletes are at elevated risk of deficiency because of iron losses through sweat, foot-strike hemolysis (red blood cell destruction from repetitive impact), and, in female athletes, menstruation. Iron deficiency without anemia, where iron stores are low but you’re not technically anemic, is diagnosed when ferritin levels drop below 30 nanograms per milliliter. Some researchers set the bar higher, considering levels below 100 as functionally deficient for athletes. For those training at altitude, ferritin levels of 40 to 90 or above are recommended before beginning a training camp.
Vitamin D supports bone health, immune function, and muscle performance. Blood levels below 30 nanograms per milliliter are considered deficient, though some research suggests athletes need levels of 50 or above for optimal benefits. Athletes who train indoors or live at higher latitudes are at particular risk.
Supplements With Strong Evidence
The supplement industry is enormous, but only a handful of products have solid evidence behind them. The Australian Institute of Sport maintains a classification system that ranks supplements by the strength of their scientific support. The top tier, Group A, includes:
- Caffeine: improves endurance, power output, and focus
- Creatine monohydrate: increases strength, power, and lean mass by helping regenerate your muscles’ short-term energy supply
- Beetroot juice (dietary nitrate): enhances blood flow and oxygen efficiency, particularly in endurance activities
- Beta-alanine: buffers acid buildup in muscles during high-intensity efforts lasting one to four minutes
- Sodium bicarbonate: also buffers muscle acidity, benefiting repeated sprint and high-intensity efforts
Sports drinks, gels, bars, and protein supplements are also in this top category, not because they contain anything exotic, but because they offer a convenient way to deliver carbohydrates, electrolytes, and protein when whole foods aren’t practical (mid-race, for example, or immediately post-training).
How Nutrition Differs by Sport
Endurance athletes and strength athletes share the same nutritional building blocks, but the proportions shift. An endurance athlete running or cycling for hours daily needs carbohydrates at the top of the range (8 to 12 grams per kilogram) to keep glycogen stores full, with protein in the 1.2 to 2.0 range. A strength or power athlete prioritizes protein (1.6 to 2.2 grams per kilogram or higher) to support muscle growth, with carbohydrate needs closer to 5 to 7 grams per kilogram. Fat intake stays relatively stable across both types, at 20 to 35 percent of total calories.
These aren’t rigid categories. A soccer player sprinting repeatedly for 90 minutes has both endurance and power demands. A CrossFit athlete combines heavy lifting with metabolic conditioning. In practice, most athletes fall somewhere on a spectrum, and their nutrition should reflect the specific blend of energy systems their sport requires. The consistent theme across all sports is the same: eat enough total calories, distribute protein throughout the day, match carbohydrate intake to training intensity, stay hydrated, and address any micronutrient gaps before they become performance problems.