Methodologic considerations for measuring energy expenditure differences between diets varying in carbohydrate using...

Area of Science:

• Human metabolism and nutrition
• Dietary interventions and energy balance
• Biomarkers of energy expenditure

Background:

• Previous studies using doubly labeled water (DLW) suggested low-carbohydrate diets increase energy expenditure.
• Respiratory chamber measurements did not corroborate these DLW findings, raising questions about the accuracy of respiratory quotient (RQ) estimations in DLW calculations.

Purpose of the Study:

• To investigate energy expenditure differences between baseline and ketogenic diets.
• To compare DLW measurements with respiratory chamber and body composition data within an energy balance framework.

Main Methods:

• 17 men with overweight/obesity underwent month-long baseline and ketogenic diets.
• Energy expenditure was measured using DLW, respiratory chambers, and energy balance calculations (DXA and intake).
• Physical activity and exercise efficiency were monitored using accelerometers.

Main Results:

• Neither respiratory chamber nor energy balance measurements showed significant changes in energy expenditure between diets.
• Unadjusted DLW measurements indicated a higher energy expenditure on the ketogenic diet, but this difference disappeared when adjusted for energy balance.
• After outlier removal, adjusted DLW results showed no significant increase in energy expenditure.

Conclusions:

• Inaccurate RQ estimation in DLW calculations may erroneously suggest increased energy expenditure on low-carbohydrate diets.
• When accounting for diet-specific energy imbalance effects on RQ, low-carbohydrate diets do not substantially increase energy expenditure.