Introduction: Malnutrition has always been a problem in CF (cystic fibrosis) patients; however, new treatments with CFTR (cystic fibrosis transmembrane conductance regulator protein) modulators have led to weight gain, with some patients at risk of overweight and obesity. Objective: Our study aimed to analyze the evolution of BMI (body mass index) after one year of treatment with triple therapy and the factors associated with weight gain in CF patients undergoing treatment with triple therapy with CFTR protein modulators (ETI) (elexacaftor/tezacaftor/ivacaftor). Methods: We conducted a prospective, observational, longitudinal, multicenter study in patients diagnosed with cystic fibrosis, aged 18 years or older, with at least one F508del allele and who underwent ETI therapy for at least one year, from 2020 to 2023. One hundred and eight patients from two cystic fibrosis units in Spain, Princess University Hospital of Madrid (74 patients) and Central University Hospital of Asturias (HUCA) (34 patients), were included. Demographic data, anthropometric data, lung function, and exacerbations were collected, comparing the data in the previous year to the start of therapy with the results after one year of treatment. Multivariant models were developed to account for repeated weight and BMI measurements, using a mixed effects model approach and accounting for possible modifying factors Results: One hundred and eight patients were included in the study, 58 men (53.7%) and 50 women (46.3%) with a mean age of 29.5 ± 9.4 years (18–59). Patient weight and BMI were recorded at baseline and at 3-month intervals during the study period. The weight increased from 59.6 kg to 62.6 kg and BMI increased from 21.9 kg/m2 to 23.0 kg/m2 after one year of treatment (p < 0.0001 for both). The proportion of underweight individuals decreased after one year of ETI therapy, from 9.3% to 1.9%, while the proportion of overweight or obese individuals increased from 8.3% to 22.9 % at the same time (p < 0.001). In relation to exacerbations, there is a significant increase in the number of patients who did not have any exacerbations after one year of treatment, which increased from 10.2% to 46.2% (p < 0.001), while the number of patients who had >4 exacerbations decreased significantly, from 40.7% to 1.9% (p < 0.001). FEV1% (forced expiratory volume) increased from 63.9 ± 20.9 to 76.8 ± 21.4 (p < 0.001) and the VR/TLC (residual volume/total lung capacity) value decreased from 45.1 ± 10.9 to 34.9 ± 6.2 (p < 0.001). The proportion with FEV1% > 80% increased from 23.1% before ETI therapy to 49.1% one year after ETI therapy. We performed multivariate mixed models to evaluate the evolution of BMI changes with time, accounting for repeated measures and for possible modifying factors. After the introduction of the triple therapy, patients included in the study had significant weight gain during the 12 months, and when including different covariates in the multivariate mixed model, we found that lower baseline BMI, lower baseline FEV1 and FVC (forced vital capacity), and higher VR/TLC value and higher number of exacerbations were associated with higher BMI changes over the study period. Conclusions: CF patients treated with triple therapy experience significant weight gain, increasing the proportion of overweight patients. CF patients who experienced greater weight gain were those with worse BMI at the start of treatment, as well as patients with worse lung function and a greater number of exacerbations in the year before starting ETI therapy.
