Background:
Obesity is a disease of fat storage and reduced fasting fat utilization, commonly assessed from Respiratory Quotient (RQ) using Indirect Calorimetry (IC), impacts weight, weight regain and health (1). Measurement of RQ could provide a basis for individualised nutritional intervention and successful obesity management. However the cost and complexity of present day technology precludes its widespread use in the clinical setting (2).
Objectives:
To assess the value of RQ measurement in the clinical setting, we investigated how different the fasting RQ (and fat utilisation) of 282 overweight and obese adults attending a primary care clinic in Western Australia, compared to normative data indicating an RQ of 0.81 corresponding to a fuel utilization ratio of <62% Fat and >38% CHO (3).
Material and Methods:
We conducted a retrospective analysis of metabolic data measured using ECAL, an Indirect Calorimeter (IC) (ETSA, Australia) (4). Respiratory Exchange Ratio (RER) was measured during testing, and is equivalent to RQ and fuel utilization at a cellular level (5). Subjects were instructed to observe a shortened 4 hour fasting protocol developed for clinical practice (6).
Results:
171 (60.6%) of subjects recorded sub-optimal fat utilization defined as having RQ > 0.81 (3). Six subjects who have fasted for 8-10 hrs have been excluded. For the 4-8 hr fasted subjects, 93 (56.4%) have an RQ > 0.81. For the >10 hr fasted subjects, 74 (66.7%) have an RQ > 0.81. Overall, more than half of the subjects exhibited sub-optimal fat utilization whether they have fasted 4-8 hrs or >10 hrs, suggesting the importance of RQ and IC for the clinical management of the overweight and obese.
Conclusion:
The results suggest that assumptions of fat utilisation have limited value for obese and overweight individuals and highlight the need for measurement of RQ to individualize obesity management.