Energy density and weight change in a long-term weight-loss trial

Background: Health risks linked to obesity and the difficulty most have in achieving weight loss underscore the importance of identifying dietary factors that contribute to successful weight loss. Methods: This study examined the association between change in dietary energy density and weight loss over time. Subjects were 213 men and women with BMI of 30-39 kg/m² and without chronic illness enrolled in 2004 in a randomized trial evaluating behavioral treatments for long-term weight loss. Subjects completed a 62-item food frequency questionnaire at baseline and at 6, 12, and 18 months. Results: Pearson correlations between BMI and energy density (kcals/g of solid food) at baseline were not significantly different from zero (r = -0.02, p = 0.84). In a longitudinal analysis, change in energy density was strongly related to change in BMI. The estimated β for change in BMI (kg/m²) of those in the quartile representing greatest decrease in energy density at 18 months compared to those in the quartile with the least was -1.95 (p = 0.006). The association was especially strong in the first six months (estimated β = -1.43), the period with greatest weight loss (mean change in BMI = -2.50 kg/m² from 0-6 months vs. 0.23 kg/m² from 12-18 months) and the greatest contrast with respect to change in energy density. Conclusion: Decreased energy density predicted weight loss in this 18 month weight loss study. These findings may have important implications for individual dietary advice and public health policies targeting weight control in the general population.