Objective To analyse the association between cardiovascular and mental comorbidities of obesity and weight loss registered in the electronic primary healthcare records.

Design and setting Longitudinal study of a cohort of adult patients assigned to any of the public primary care centres in Aragon, Spain, during 2010 and 2011.

Participants Adult obese patients for whom data on their weight were available for 2010 (n=62 901), and for both 2010 and 2011 (n=42 428).

Outcomes Weight loss (yes/no) was calculated based on the weight difference between the first value registered in 2010 and the last value registered in 2011. Multivariate logistic regression models were adjusted for individuals’ age, sex, total number of chronic comorbidities, type of obesity and length of time between both weight measurements.

Results According to the recorded clinical information, 9 of 10 obese patients showed at least one chronic comorbidity. After adjusting for covariates, weight loss seemed to be more likely among obese patients with a diagnosis of diabetes and/or dementia and less likely among those with hypertension, anxiety and/or substance use problems (p<0.05). The probability of weight loss was also significantly higher in male patients with more severe obesity and older age.

Conclusions An increased probability of weight loss over 1 year was observed in older obese male patients, especially among those already manifesting high levels of obesity and severe comorbidities such as diabetes and/or dementia. Yet patients with certain psychological problems showed lower rates of weight reduction. Future research should clarify if these differences persist beyond potential selective weight documentation in primary care, to better understand the trends in weight reduction among obese patients and the underlying role of general practitioners regarding such trends.