Most workout nutrition advice circles back to the same short list. Five nutrient categories produce the bulk of measurable performance and recovery effects in trained athletes. Anything outside that list typically lives at the margins of the evidence base, where small effect sizes hide inside large person-to-person variation. The five categories below are the ones backed by trial data strong enough to recommend without caveats.
1. Carbohydrates as the Primary Fuel
Carbohydrate availability sets the ceiling on workout intensity past the 90-minute mark. Liver and muscle glycogen stores hold roughly 1,800 to 2,200 calories in a trained adult. High-intensity intervals can deplete muscle glycogen in localized fibers within 20 minutes, which is why repeat sprint sessions feel harder as they progress. The body is using up its glucose stockpile faster than it can pull glucose from the bloodstream.
Daily carbohydrate intake for active adults sits around 5 to 8 grams per kilogram of body weight, and rises toward 8 to 10 grams per kilogram during heavy training blocks. Intake during workouts longer than 90 minutes should fall between 40 and 80 grams per hour. A glucose-to-fructose mixture in a 2:1 ratio raises the maximum oxidation ceiling above what plain glucose can hit, because the small intestine has separate transporters for each sugar.
Pre-workout carbohydrate loading raises starting glycogen by 20 to 50% in trained athletes who eat 8 to 12 grams per kilogram in the 24 to 48 hours before a long event. The effect is largest for sessions over two hours and small for sessions under 90 minutes. Lifting and short sprint work do not benefit from loading at the same rate.
2. Protein for Repair and Adaptation
Resistance training and long endurance sessions damage muscle protein at the fiber level. The body rebuilds those fibers with stronger and slightly more numerous proteins, which is the molecular substance of training adaptation. Daily protein intake of 1.2 to 1.7 grams per kilogram supports this rebuilding for most active adults, with strength athletes sitting at the upper end of the range.
Leucine is the amino acid that triggers the rebuilding signal. A meal or shake containing 2.5 to 3 grams of leucine, which roughly equals 25 to 30 grams of high-quality protein, produces a near-maximal protein synthesis response. More leucine in the same meal does not produce a larger response. Spreading protein intake across three to four meals across the day raises 24-hour protein synthesis above what one or two large doses produce.
Whole-food protein and isolated protein powders produce equivalent muscle outcomes when total daily protein hits the target. Powders are a convenience format, useful when chewing solid food after hard work feels difficult or when travel limits meal access. They do not extend the effect beyond what cottage cheese, eggs, fish, beans, or lean meat can provide at the same protein dose.
3. Electrolytes for Sweat Replacement
Sweat carries sodium at concentrations between 20 and 80 millimoles per liter, with substantial person-to-person variation. A 70-kilogram athlete losing 1.5 liters of sweat per hour at typical concentrations is shedding 700 to 2,000 milligrams of sodium per hour. Smaller losses of potassium, magnesium, and calcium occur in parallel. Plain water does not replace any of this, and consumed in large volumes during long sessions, it can dilute blood sodium below the 135 millimole per liter threshold for hyponatremia. The Northwestern Medicine editorial on how electrolytes boost hydration makes the same point with practical examples.
A trained athlete using an electrolyte powder for hydration during a long workout typically targets 300 to 700 milligrams of sodium per hour, with potassium and magnesium included at fixed ratios.
The replacement target depends on sweat rate, sodium concentration, and ambient conditions. Salty sweaters in heat can require the upper end of the range, while small athletes in cool weather usually do well at the lower end. Pre-weighing before a workout and weighing again afterward gives a usable sweat-rate estimate, and a follow-up sodium-loss test from a sports nutritionist refines the number further.
4. Iron for Oxygen Transport
Iron is the central atom of hemoglobin, the protein that ferries oxygen from the lungs to working muscles. Active adults lose iron through sweat, gastrointestinal microbleeding, and in female athletes through menstruation. Studies of endurance running cohorts have reported low ferritin in more than half the women sampled and in roughly a third of the men. The functional consequence is reduced oxygen delivery, which shows up as flat workouts and rising heart rate at the same pace.
Serum ferritin below 25 nanograms per milliliter is the threshold most sports medicine clinics use as a flag for low iron stores. Supplementation is appropriate after a blood test confirms low levels and not before. The reference profile for iron deficiency anemia maintained by the NHS sets out the standard symptoms and the typical clinical workup. Casual high-dose iron use in non-deficient adults can produce gastrointestinal side effects and rare iron overload.
5. Magnesium for Muscle Function
Magnesium is a cofactor for more than 300 enzymes, including those that produce ATP from glucose and fat. It also regulates the calcium signaling that triggers muscle contraction. Subclinical magnesium deficiency is common in adults who eat low-vegetable, low-whole-grain diets, and active adults need 10 to 20% more magnesium than the recommended daily intake of 320 milligrams for women and 420 milligrams for men.
The standard reference on magnesium benefits maintained by UCLA Health summarizes both the documented effects on muscle, nerve, and bone health and the limited evidence for routine high-dose supplementation. Supplementation in adults with adequate intake does not raise serum magnesium and does not improve performance. Athletes with genuine deficiency often report fewer cramps and better sleep within four to eight weeks of correction.
Food sources cover most needs without a pill. A handful of almonds delivers 80 milligrams. A cup of cooked spinach delivers 150. Black beans, dark chocolate, and pumpkin seeds each deliver 100 to 150 milligrams per serving. An adult who eats two to three servings of these foods daily rarely needs supplementation.
What the Five Categories Have in Common
Every entry on this list has a defined physiological pathway, a measurable blood marker or sweat marker that signals deficiency, and a body of trial data that links correction to improved performance or reduced injury rate.
Carbohydrate fuels the work. Protein rebuilds the structure. Electrolytes preserve fluid balance. Iron carries oxygen. Magnesium runs the enzyme system that ties it all together. The 30-minute window for protein after workout intake gets most of the popular attention, but daily totals across all five categories matter more than any single timing rule. An athlete who hits the daily targets on each of these five does not need to chase exotic supplements to fill in the gaps.