Obesity is a common comorbidity of asthma that is associated not only with development of the disease, but also with poorer disease control and greater severity. Recent prospective evidence supports the idea that body weight gain precedes the development of asthma, although the debate is far from over. The objective of this document is to conduct a systematic review of 3 clinical questions related to asthma and obesity: (a) Obesity and asthma: the chicken or the egg? Clinical insights from epidemiological and phenotyping studies. (b) Is obesity a confounding factor in the diagnosis and management of asthma, especially in severe or difficult-to-control asthma? (c) How do obese asthma patients respond to pharmacological treatments and to biological drugs? Do we have effective specific interventions?
Revised epidemiological, pathological, and mechanistic evidence combined with data from interventional clinical trials prevent us from clearly stating that obesity causes asthma. However, the complexity and heterogeneity of both illnesses make several clinical scenarios possible. Furthermore, asthma represents an additional clinical challenge in the obese patient. Physicians need to be aware of the confounding effects created by the more marked perception of symptoms, alterations in lung function, and the various comorbidities that obese persons present. Exhaustive phenotyping of the obese asthma patient should enable us to develop a rational therapeutic plan, including both the pharmacological approach and specific antiobesity therapies such as combining diet and exercise and, in extreme cases, bariatric surgery.

Key words: Asthma, Obesity, Diet, Exercise, Phenotypes, Comorbidity, Asthma treatment