As atopy, asthma, and obesity increased in the last decades, it was reasonable to speculate that maybe they are linked. When evaluating the effect of the Mediterranean diet, it was reported that obesity was a risk factor for current severe asthma in girls. A practical measurement of total body fat is the estimation of body mass index (BMI)–weight/height ratio.
However, controversies about the relationship of BMI with the presence of atopy and asthma is shown by a report from Australia, which states that increased BMI was a risk factor for cough, ever wheezing and atopy (predominantly in girls), but not for diagnosed asthma or bronchial hyper-responsiveness. Without these last
two conditions, it is difficult to be conclusive, as gastro-esophageal reflux, sleep disorders, being unfit, or altered mechanical ventilation could explain symptoms, and all are associated with overweight.
So some meta-analysis was required to elucidate the real impact of overweight in the incidence of asthma, and 1 with a sample larger than 300,000, evidenced a dose–response increasing odds for incident asthma: odds ratio (OR) 1.38 for normal versus overweight comparison, and OR 1.92 for obesity; none of them was
affected by sex. These odds have a huge impact on populations like the USA, where more than 60% of adults are overweight/obese, and in consequence at risk of developing asthma.
Also considering a meta-analysis in children, the same evidence was reported. The relative risk (RR) of high birth weight on developing asthma later was RR = 1.2 (95% confidence interval (CI) 1.1–1.3), while the effect of overweight in middle childhood was RR = 1.5 (95% CI 1.2–1.8) [31]. Misclassification, diagnostic
bias, and individual confounders are always doubts emerging from meta-analysis; however, the results from an enormous cohort study, from childhood to adulthood, are the only possibility to corroborate or contradict this evidence.
