Dietary energy density in the treatment of obesity: a year-long trial comparing 2 weight-loss diets

Abstract

Background: Consuming foods low in energy density (kcal/g) decreases energy intake over several days, but the effectiveness of this strategy for weight loss has not been tested.

Objective: The effects on weight loss of 2 strategies for reducing the energy density of the diet were compared over 1 y.

Design: Obese women (n = 97) were randomly assigned to groups counseled either to reduce their fat intake (RF group) or to reduce their fat intake and increase their intake of water-rich foods, particularly fruit and vegetables (RF+FV group). No goals for energy or fat intake were assigned; the subjects were instructed to eat ad libitum amounts of food while following the principles of their diet.

Results: After 1 y, study completers (n = 71) in both groups had significant decreases in body weight (P < 0.0001). Subjects in the RF+FV group, however, had a significantly different pattern of weight loss (P = 0.002) than did subjects in the RF group. After 1 y, the RF+FV group lost 7.9 +/- 0.9 kg and the RF group lost 6.4 +/- 0.9 kg. Analysis of all randomly assigned subjects also showed a different pattern of weight loss between groups (P = 0.021). Diet records indicated that both groups had similar reductions in fat intake. The RF+FV group, however, had a lower dietary energy density than did the RF group (P = 0.019) as the result of consuming a greater weight of food (P = 0.025), especially fruit and vegetables (P = 0.037). The RF+FV group also reported less hunger (P = 0.003).

Conclusion: Reducing dietary energy density, particularly by combining increased fruit and vegetable intakes with decreased fat intake, is an effective strategy for managing body weight while controlling hunger.

FIGURE 1

Flow diagram of subject enrollment, random assignment, and completion of the study protocol.

FIGURE 2

Mean (± SEM) change in body weight for study completers in the reduced-fat (RF) and reduced-fat plus increased fruit and vegetable (RF+FV) intervention groups over time. Random coefficients analysis was used to model the longitudinal response over time, with control for baseline values. The group × time interaction (P = 0.002) indicates that the response over time differed between the groups. The interaction remained significant (P = 0.021) when all randomly assigned subjects were included in the analysis. Baseline values did not differ significantly between the groups (unpaired t test).

FIGURE 3

Mean (± SEM) food energy density (kcal/g) for study completers in the reduced-fat (RF) and reduced-fat plus increased fruit and vegetable (RF+FV) intervention groups over time. Differences in dietary energy density between the groups were determined from a mixed linear model with repeated measures, by using all available time points and with control for baseline values. The group × time interaction was significant (P = 0.019), which indicated that dietary energy density was significantly less in the RF+FV group than in the RF group during the intervention. Baseline values did not differ significantly between the groups (unpaired t test).