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In this consensus statement on immunonutrition and exercise, a panel of knowledgeable contributors from across the globe provides a consensus of updated science, including the background, the aspects for which a consensus actually exists, the controversies and, when possible, suggested directions for future research., (Copyright © 2016 International Society of Exercise and Immunology. All rights reserved.)

The gut microbiota consists of a cluster of microorganisms that produces several signaling molecules of a hormonal nature which are released into the blood stream and act at distal sites. There is a growing body of evidence indicating that microbiota may be modulated by several environmental conditions, including different exercise stimulus, as well some pathologies. Enriched bacterial diversity has also been associated with improved health status and alterations in immune system, making multiple connections between host and microbiota. Experimental evidence has shown that reduced levels and variations in the bacterial community are associated with health impairments, while increased microbiota diversity improves metabolic profile and immunological responses. So far, very few controlled studies have focused on the interactions between acute or chronic exercise and the gut microbiota. However, some preliminary experimental data obtained from animal studies or probiotics studies show some interesting results at the immune level, indicating that the microbiota also acts like an endocrine organ and is sensitive to the homeostatic and physiological changes associated with exercise. Thus, our review intends to shed some light on the interaction between gut microbiota, exercise and immunomodulation., (Copyright © 2015 International Society of Exercise and Immunology. All rights reserved.)

The physical training undertaken by athletes is one of a set of lifestyle or behavioural factors that can influence immune function, health and ultimately exercise performance. Others factors including potential exposure to pathogens, health status, lifestyle behaviours, sleep and recovery, nutrition and psychosocial issues, need to be considered alongside the physical demands of an athlete's training programme. The general consensus on managing training to maintain immune health is to start with a programme of low to moderate volume and intensity; employ a gradual and periodised increase in training volumes and loads; add variety to limit training monotony and stress; avoid excessively heavy training loads that could lead to exhaustion, illness or injury; include non-specific cross-training to offset staleness; ensure sufficient rest and recovery; and instigate a testing programme for identifying signs of performance deterioration and manifestations of physical stress. Inter-individual variability in immunocompetence, recovery, exercise capacity, non-training stress factors, and stress tolerance likely explains the different vulnerability of athletes to illness. Most athletes should be able to train with high loads provided their programme includes strategies devised to control the overall strain and stress. Athletes, coaches and medical personnel should be alert to periods of increased risk of illness (e.g. intensive training weeks, the taper period prior to competition, and during competition) and pay particular attention to recovery and nutritional strategies.

Upper Respiratory Tract Infection (URTI) is regarded as the most common medical condition affecting both highly trained and elite athletes, in particular those participating in endurance events. The causes of these disturbances, also occurring during training, remain unclear. Viruses such as rhinovirus, adenovirus and para-influenza virus are frequently reported as the source of URTI. However, in a few comprehensive laboratory and epidemiological studies which reported at least a 30% incidence of URTI, no identifiable pathogens were either reported or studied. A recent, longitudinal study investigated symptomatology and pathogenic etiology in sedentary controls, recreational and elite athletes. The highest incidence of URTI occurred in elite athletes. However; only 11 out of 37 illness episodes overall had pathogenic origins, and most of the unidentified upper respiratory illnesses were shorter in duration and less severe than infectious ones. This concept of inflammation without infection in athletes is quite new and leads us to consider other explanatory pathophysiological conditions. Increases in airway neutrophils, eosinophils and lymphocytes have been described under resting conditions in endurance sports, swimmers and cross-country skiers. These inflammatory patterns may be due to pollutants or chlorine-related compounds in swimmers. After intense exercise similar airways cellular profiles have been reported, with a high amount of bronchial epithelial cells. This increase in airway inflammatory cells in athletes can result from a hyperventilation-induced increase in airway osmolarity stimulating bronchial epithelial cells to release chemotactic factors. Fortunately, in most cases, these inflammatory cells express rather low level of adhesion molecules, explaining why airway inflammation may appear blunted in athletes despite numerous inflammatory cellular elements. However it can be hypothesized that a transient loss of control of this local inflammation, due to various external physico-chemical strains, might occur. This might account for some of the unidentified upper respiratory illnesses.