Nutritional Requirements

Immune support by micronutrients is historically based on vitamin C deficiency and supplementation in scurvy in early times. It has since been established that the complex, integrated immune system needs multiple specific micronutrients, including vitamins A, D, C, E, B6, and B12, folate, zinc, iron, copper, and selenium, which play vital, often synergistic roles at every stage of the immune response. Adequate amounts are essential to ensure the proper function of physical barriers and immune cells; however, daily micronutrient intakes necessary to support immune function may be higher than current recommended dietary allowances. Certain populations have inadequate dietary micronutrient intakes, and situations with increased requirements (e.g., infection, stress, and pollution) further decrease stores within the body. Several micronutrients may be deficient, and even marginal deficiency may impair immunity. Although contradictory data exist, available evidence indicates that supplementation with multiple micronutrients with immune-supporting roles may modulate immune function and reduce the risk of infection. Micronutrients with the strongest evidence for immune support are vitamins C and D and zinc. Better design of human clinical studies addressing dosage and combinations of micronutrients in different populations are required to substantiate the benefits of micronutrient supplementation against infection.

The gut microbiota is a changing ecosystem, containing trillions of bacteria, continuously shaped by many factors, such as dietary habits, seasonality, lifestyle, stress, antibiotics use, or diseases. A healthy host-microorganisms balance must be respected in order to optimally maintain the intestinal barrier and immune system functions and, consequently, prevent disease development. In the past several decades, the adoption of modern dietary habits has become a growing health concern, as it is strongly associated with obesity and related metabolic diseases, promoting inflammation and both structural and behavioral changes in gut microbiota. In this context, novel dietary strategies are emerging to prevent diseases and maintain health. However, the consequences of these different diets on gut microbiota modulation are still largely unknown, and could potentially lead to alterations of gut microbiota, intestinal barrier, and the immune system. The present review aimed to focus on the impact of single food components (macronutrients and micronutrients), salt, food additives, and different dietary habits (i.e., vegan and vegetarian, gluten-free, ketogenic, high sugar, low FODMAP, Western-type, and Mediterranean diets) on gut microbiota composition in order to define the optimal diet for a healthy modulation of gut microbiota.

As humans age, the risk and severity of infections vary in line with immune competence according to how the immune system develops, matures, and declines. Several factors influence the immune system and its competence, including nutrition. A bidirectional relationship among nutrition, infection and immunity exists: changes in one component affect the others. For example, distinct immune features present during each life stage may affect the type, prevalence, and severity of infections, while poor nutrition can compromise immune function and increase infection risk. Various micronutrients are essential for immunocompetence, particularly vitamins A, C, D, E, B2, B6, and B12, folic acid, iron, selenium, and zinc. Micronutrient deficiencies are a recognized global public health issue, and poor nutritional status predisposes to certain infections. Immune function may be improved by restoring deficient micronutrients to recommended levels, thereby increasing resistance to infection and supporting faster recovery when infected. Diet alone may be insufficient and tailored micronutrient supplementation based on specific age-related needs necessary. This review looks at immune considerations specific to each life stage, the consequent risk of infection, micronutrient requirements and deficiencies exhibited over the life course, and the available evidence regarding the effects of micronutrient supplementation on immune function and infection.

The purpose of this narrative review is to provide an evidence-based update on the protein needs of endurance athletes with a focus on high-quality metabolic studies conducted on the topics of recovery and training adaptation over the past decade. We use the term 'protein needs' to delineate between the concepts of a daily protein requirement and per meal protein recommendations when devising scientific evidence-based protein guidelines for the endurance athlete to promote post-exercise recovery, enhance the adaptive response to endurance training and improve endurance performance. A habitual protein intake of 1.5 g/kg of body mass (BM)-1·day-1 is typical in male and female endurance athletes. Based on findings from a series of contemporary protein requirement studies, the evidence suggests a daily protein intake of ~ 1.8 g·kgBM-1·day-1 should be advocated for endurance athletes, with the caveat that the protein requirement may be further elevated in excess of 2.0 g·kgBM-1·day-1 during periods of carbohydrate-restricted training and on rest days. Regarding protein recommendations, the current lack of metabolic studies that determine the dose response of muscle protein synthesis to protein ingestion in relation to endurance exercise makes it difficult to present definitive guidelines on optimal per meal protein intakes for endurance athletes. Moreover, there remains no compelling evidence that co-ingesting protein with carbohydrate before or during endurance exercise confers any performance advantage, nor facilitates the resynthesis of liver or muscle glycogen stores during recovery, at least when carbohydrate recommendations are met. However, recent evidence suggests a role for protein nutrition in optimising the adaptive metabolic response to endurance training under conditions of low carbohydrate and/or energy availability that represent increasingly popular periodised strategies for endurance athletes.