Predicting Glycemic Control in Patients With Impaired Fasting Glucose With Fasting Respiratory Exchange Ratio

Impaired metabolic flexibility is associated with prediabetes. However, its assessment with reference methods is impractical in routine clinical practice.

This study investigates the relationship between fasting respiratory exchange ratio (RER), measured through indirect calorimetry, and glucose metabolism in individuals with prediabetes.

The study involved 2 cohorts: (1) a cross-sectional cohort of 10 176 individuals to assess the association between fasting RER and glucose metabolism parameters, and (2) a matched longitudinal cohort of 86 patients with impaired fasting glucose, categorized into fat oxidation (RER < 0.775) and glucose oxidation (RER > 0.925) groups, to evaluate the impact of fasting RER on impaired fasting glucose resolution and fasting glucose after a 1-year lifestyle intervention.

In the cross-sectional cohort, a higher fasting RER was associated with higher fasting glucose, insulin, and Homeostatic Model Assessment for Insulin Resistance. In the longitudinal cohort, the fat oxidation group showed a greater reduction in fasting glucose (+5.9; 95% CI 1.4, 10; P = .011) and a higher probability of achieving normal fasting glycemia (log(odds ratio) -0.89; 95% CI -1.8, -0.03; P = .046) after the intervention, despite similar weight loss between groups.

Our findings suggest that fasting RER, a readily accessible clinical measure, can provide valuable insights into glucose metabolism and impaired fasting glucose resolution. A lower fasting RER, indicative of a greater capacity for fat oxidation, is associated with improved glycemic control after a lifestyle intervention.