Obesity and asthma are associated, but the mechanism(s) of the association have yet to be elucidated. The aim of this study was to assess airway inflammation in relation to obesity and plasma fatty acids in males and females with and without asthma.Obese (n=68) and nonobese (n=47) adults with asthma, and obese (n=16) and nonobese (n=63) healthy controls had induced sputum and venous blood samples analysed for inflammatory markers.There was a positive interaction between obesity and asthma on sputum neutrophil percentage (p=0.012) and C-reactive protein level (p=0.003). Although sputum eosinophil percentage was elevated in asthma (p=0.001), there was no effect of obesity (p=0.16). Sputum neutrophil percentage was positively associated with body mass index in females with asthma (β=1.015, 95% CI 0.258–1.772; p=0.009) and neutrophilic asthma was present in a greater proportion of obese compared with non-obese females (42.9%versus16.2%; p=0.017). In males with asthma, sputum neutrophil percentage was positively associated with total plasma saturated fatty acids (β=0.108, 95% CI 0.036–0.180; p=0.004) and negatively with monounsaturated fatty acids (β= -0.068, 95% CI -0.131– -0.005; p=0.035).This was the first study to demonstrate an increase in neutrophilic airway inflammation in obese asthma. This relationship was significant only in females with asthma. In males, saturated and monounsaturated fatty acids were important predictors of neutrophilic airway inflammation in asthma.

Oxidative stress, specifically lipid peroxidation, is believed to contribute to the pathophysiology of asthma. This review highlights the pathways through which reactive oxygen species (ROS) may lead to lipid peroxidation. The potential of both the innate and acquired immune systems to activate inflammatory cells and release ROS that may overwhelm the host antioxidant defences and cause lipid peroxidation, accompanied by detrimental pathophysiological effects, are discussed.Despite the evidence demonstrating the importance of lipid peroxidation, systematic characterisation of oxidative stress and antioxidant defences has not been undertaken, largely due to the lack of appropriate biomarkers. This review discusses the emergence of isoprostanes (specifically 8‐iso­prostaglandin F_2α) as reliable,in vivomarkers of lipid peroxidation, which provides an appropriate tool for studying oxidative stress. Furthermore, the development of techniques to study induced sputum and breath condensate, derived directly from the airway surface, enables the site of oxidative damage to be closely assessed.Evidence suggests that dietary changes that have occurred over recent years have increased susceptibility to lipid peroxidation, due to reduced antioxidant defences. To date, the limited number of long­term (>1 week) supplementation trials have been promising. However, the development of techniques to study isoprostanes in airway­lining fluid pave the way for further studies investigating the potential for antioxidant supplements to be used as routine therapy in asthma.

Background: Antioxidant-rich diets are associated with reduced asthma prevalence in epidemiologic studies. We previously showed that short-term manip