Markers of respiratory function response to high‐carbohydrate and high‐fat intake in patients with lung diseases: a systematic review with meta‐analysis of randomized clinical trials

Macronutrients can differently affect respiratory function markers such as VO2 , VCO2 , PaO2 , PaCO2 , and respiratory quotients (RQs), but systematic appraisal of the evidence on randomized clinical trials (RCTs) is lacking.The objective of this work is to compare the response of respiratory function markers with high-carbohydrate and high-fat intake in patients with lung diseases.Systematic review conducted according to Cochrane Collaboration recommendations, reported following Preferred Reporting Items for Systematic Reviews and Meta-Analysis for pairwise systematic reviews of interventions 2020. PubMed, EMBASE, Scopus, and Cochrane CENTRAL were searched up to July 2021. Two reviewers selected the RCTs and extracted the data. Risk of bias and the certainty of evidence were assessed by RoB 2 and Grading of Recommendations Assessment, Development, and Evaluation System criteria, respectively. Statistical and graphical data guided the publication bias investigation. Meta-analyses were conducted.We included 14 RCTs (362 participants), four of which were parallel. Most studies included patients with chronic obstructive pulmonary disease. High-fat intake decreased VCO2 (mean difference [MD] = -35.89 ml/min [95% confidence interval (CI), -45.24 to -26.21]); I² = 0%), VO2 (MD = -29.30 ml/min [95% CI, -40.94 to -17.66]; I² = 0%), PaCO2 mm Hg (MD = -4.62 [95% CI, -7.67 to -1.58]; I² = 84%), and RQ (MD = -0.08 [95% CI, -0.09 to -0.06]; I² = 0%) in the subset of parallel RCTs. In crossover RCTs, there was generally no evidence of effect except for a greater decrease in RQ (MD = -0.09 [95% CI, -0.12 to -0.02]; I² = 96%) in favor of high-fat intake.High-fat intake resulted in greater reductions of VCO2 , VO2 , PaCO2 , and RQ in adult patients with lung diseases. The certainty of the evidence is very low/low, and it precludes a specific recommendation on macronutrients contribution to energy intake of these patients.