Marathon training repeatedly stresses the immune system through large-volume sessions, travel, and exposure to crowds. Nutritional strategies that protect immunity focus on maintaining energy availability, reducing exercise-induced immune perturbation with carbohydrate during long sessions, and supporting recovery with adequate protein and targeted micronutrient monitoring. Research-based guidance helps translate these principles into practice.
Energy availability and carbohydrates
Maintaining sufficient energy intake relative to training load is central. Sustained low energy availability impairs immune cell function and raises illness risk. David C. Nieman at Appalachian State University has shown that ingesting carbohydrate before and during prolonged running attenuates the transient rise in stress hormones and some markers of immune disturbance seen after long exercise bouts. Periodizing carbohydrate to match session intensity and duration preserves performance while lowering immunological strain. For practical application emphasize regular meals and snacks around long runs, and use carbohydrate sources that are tolerated during hard sessions to avoid additional gastrointestinal stress.
Protein, micronutrients, and supplements
Adequate protein supports repair and the generation of immune cells. Sports nutrition experts such as Louise Burke at the Australian Institute of Sport advise spreading moderate protein servings across the day and prioritizing leucine-rich foods after key sessions. Micronutrients matter where deficiency is common. Screening for iron status is essential, especially for female runners, because iron deficiency reduces aerobic capacity and impairs immune competence. Vitamin D status should be assessed for athletes training in low-sunlight regions because low levels are associated with higher respiratory infection risk. Evidence for probiotics and selected polyphenol-rich foods indicates potential reductions in upper respiratory symptoms for some athletes, but strain-specificity and product quality determine benefit and results vary.
Poor nutritional strategies increase the likelihood of upper respiratory tract infections, lost training days, and maladaptive recovery that can compound across a training cycle. Cultural and territorial factors influence feasible choices; athletes living at high latitudes or in food-insecure settings must prioritize testing and locally available, nutrient-dense foods. Individualization is crucial: work with a sports dietitian to translate general principles into body-mass specific energy plans, iron and vitamin D screening, and tolerable on-course fueling that together optimize immune resilience across a marathon training cycle.