Trail Nutrition Calculator

Calorie targets are derived from MET (Metabolic Equivalent of Task) values for running, scaled to body weight: kcal/hr = weight × MET × 0.0175 × 60. Trail running at race effort uses a MET of approximately 14 (Burke, 2001). Altitude increases metabolic cost by 5-12% above 1500m due to increased ventilation and reduced mechanical efficiency.

Carbohydrate absorption is limited by gut transport capacity. Research by Jeukendrup (2010) shows that glucose alone can be absorbed at ~60g/hr. Combining glucose + fructose (in a roughly 2:1 ratio, as found in most modern trail gels) raises this ceiling to ~80-90g/hr by using two separate intestinal transport pathways. The targets here follow these ceilings at each intensity level.

Fluid and sodium targets are based on Maughan & Shirreffs (2010) sweat rate research. Sweat loss increases significantly with temperature (roughly +200-600ml/hr across the cool-to-very-hot range) and moderately with altitude. Sodium replacement prevents hyponatremia (dangerously low sodium from drinking too much plain water) - a real risk in hot ultras. Ranges are shown rather than single values because individual sweat rates vary up to 3x between athletes.

Caffeine is one of the most evidence-backed ergogenic aids for endurance events (Spriet, 2014). Optimal timing is roughly 50% into the event (when fatigue starts compounding) with a dose of 1-3mg/kg. The 400mg cap reflects the threshold above which side effects (anxiety, GI distress, cardiac rhythm) can outweigh benefits.

These are starting points, not prescriptions. Individual responses to heat, altitude, and nutrition vary enormously. Practice your nutrition strategy in training runs of similar duration before relying on it in a race.

Jeukendrup AE. (2010). Carbohydrate and exercise performance. Nutr Rev. 68(S1):S82-S88. Maughan RJ, Shirreffs SM. (2010). Dehydration and rehydration in sport. Scand J Med Sci Sports. Spriet LL. (2014). Exercise and sport performance with low doses of caffeine. Sports Med. 44(S2):175-184. Burke LM. (2001). Energy needs of athletes. Can J Appl Physiol. 26(S):S202-S219.