Weight loss leads to a marked decrease in nonresting energy expenditure in ambulatory human subjects

Area of Science:

• Metabolism and Human Physiology
• Obesity and Weight Management

Background:

• Understanding long-term energy expenditure post-weight loss is crucial for obesity management.
• Previous studies have not prospectively assessed resting and nonresting energy expenditure components in ambulatory, weight-stable, reduced-obese individuals.

Purpose of the Study:

• To prospectively assess the resting and nonresting components of 24-hour energy expenditure after weight reduction in humans.
• To determine the contribution of nonresting energy expenditure to the overall decrease in energy requirements post-weight loss.

Main Methods:

• Cross-sectional study of reduced-obese and obese subjects, estimating 24-hour energy expenditure via caloric intake.
• Regression analysis to compare energy requirements between reduced-obese and never-obese individuals.
• Longitudinal study of reduced-obese men before and after weight loss to assess changes in energy expenditure components.

Main Results:

• Reduced-obese subjects showed an 18% lower daily energy requirement compared to never-obese individuals of similar body weight.
• In reduced-obese men, 24-hour energy expenditure was significantly lower than predicted by fat-free mass (FFM), while resting metabolic rate (RMR) was as predicted by FFM.
• The decrease in nonresting energy expenditure accounted for 71% of the total decrease in estimated 24-hour energy expenditure after weight loss.

Conclusions:

• Weight reduction in obese individuals leads to a substantial decrease in nonresting energy expenditure.
• Energy savings after weight loss are primarily driven by reductions in nonresting energy expenditure, not resting metabolic rate.
• These findings highlight the importance of nonresting energy expenditure in the energy balance of reduced-obese individuals.