Nutrient timing

One of the most common nutritional mistakes in endurance training is to eat the same way regardless of the training load. Athletes who eat the same way during a hundred-kilometer week as they do during a fifty-kilometer week will consistently under-recover during high-load weeks and likely overeat during lighter weeks. Adjusting nutrition to match the training load is a fundamental practice that directly impacts training adaptation, recovery speed, and long-term development.

Principle: Nutritional Periodization

Nutritional periodization is the practice of adjusting macronutrient intake—especially carbohydrates—in relation to the volume and intensity of training. The principle is simple. Carbohydrates are the primary fuel for high-intensity and high-volume training. When training demands are high, carbohydrate needs are high. When training demands are low, carbohydrate needs are lower.

This is not a complicated system. For most athletes, it does not require tracking apps or precise gram-by-gram measurements. It requires an understanding of the relationship between training load and fuel needs, and a willingness to adjust eating accordingly.

Training Week and Carbohydrate Needs

A typical ultrarunning training week includes several types of runs.

On easy running days, where intensity is low and work is primarily aerobic, fat is the primary fuel. Carbohydrate needs are moderate, approximately five to seven grams per kilogram of body weight per day.

On quality session days—intervals, tempo runs, hill repeats—intensity is high, and glycogen demand increases. Carbohydrate needs are elevated before, during, and after, approximately seven to ten grams per kilogram per day.

On long run days, a moderate-intensity three-hour or longer effort creates a high total carbohydrate requirement based purely on duration. The day requires pre-run loading, fuel during the run, and a recovery meal, totaling about eight to twelve grams per kilogram throughout the day.

On rest and recovery days, there is little training. Carbohydrate needs are at their lowest, around three to five grams per kilogram. Protein and micronutrient intake are still important to support recovery.

Practical Adaptation

Instead of precisely calculating grams each day, a practical approach is to eat more on hard days, moderately on easy days, and less on rest days. On quality session days and long run days, actively increase carbohydrate portion sizes at meals—an extra serving of rice, pasta, potatoes, or bread—and incorporate a pre-session snack and a post-session recovery meal. On easy running days, maintain normal carbohydrate portions without active augmentation. On rest days, moderately reduce carbohydrate portions and shift the focus to proteins and vegetables to support recovery and replenish micronutrient stores without excess carbohydrate energy.

Fueling During Training Runs

Race day fueling should be practiced in training. Every long run lasting over ninety minutes should be fueled at race intensity. This serves two purposes.

The first is gut training. Regular carbohydrate intake during exercise increases gut transporter capacity and gastric tolerance. The second is performance in the training itself. Under-fueled long runs result in disproportionate fatigue, slower adaptation, and a greater recovery debt. Well-fueled training leads to better sessions and faster adaptation.

A common mistake is to train without fuel to save money on nutrition products and then try to fuel optimally on race day. This approach fails to develop gut tolerance and results in stomach issues on race day with a product the gut is not accustomed to.

Training Load and Race Performance

The athletes who perform best in ultras are typically those who train most consistently. Consistent training requires consistent recovery. Consistent recovery requires adequate nutrition relative to the training load.

Chronic under-fueling in training increases the risk of injuries due to impaired tissue repair, suppresses immune system function and increases the frequency of illnesses, lowers training quality through cumulative glycogen depletion, and disrupts hormonal arrangements for sleep, mood, and motivation. Paradoxically, it also reduces fat oxidation efficiency in the long term—the body adapts to scarcity by reducing metabolic flexibility.

The cost of chronic under-fueling is not visible in any single session. It accumulates over weeks and months and manifests as stagnation, injuries, or illnesses precisely at the point in the training cycle where fitness should be peaking.

Summary

Adjust carbohydrate intake to match the training load. Eat more on hard days, moderately on easy days, and less on rest days. Fuel every long run as if it were a race. Athletes who do this consistently are those who arrive on race day healthy, well-trained, and ready to execute their fueling strategy effectively.

References

Burke LM, Hawley JA, Wong SHS, Jeukendrup AE. (2011). Carbohydrates for training and competition. Journal of Sports Sciences. 29(Suppl 1), S17–S27.

Jeukendrup AE, Killer SC. (2010). The myths surrounding pre-exercise carbohydrate feeding. Annals of Nutrition and Metabolism. 57(Suppl 2), 18–25.

Mountjoy M, Sundgot-Borgen JK, Burke LM, Ackerman KE, Blauwet C, Constantini N, et al. (2018). IOC consensus statement on relative energy deficiency in sport (RED-S): 2018 update. British Journal of Sports Medicine. 52(11), 687–697.