Portion size can be used strategically to increase vegetable consumption in adults

Abstract

Background: An increase in the proportion of vegetables at meals could help achieve recommended vegetable intakes and facilitate weight management.

Objective: We investigated the effects on food and energy intakes of varying the portion size and energy density of a vegetable that was added to a meal or substituted for other foods.

Design: In 2 experiments with crossover designs, men and women were served a meal of a vegetable, grain, and meat. Across the meals, the vegetable was served in 3 portion sizes (180, 270, or 360 g) and 2 energy densities (0.8 or 0.4 kcal/g) by altering the type and amount of added fat. In the addition study (n = 49), as the vegetable portion was increased, amounts of the grain and meat were unchanged, whereas in the substitution study (n = 48), amounts of the grain and meat decreased equally.

Results: An increase in the vegetable portion size resulted in greater vegetable consumption in both studies (mean +/- SE: 60 +/- 5 g; P < 0.0001). The addition of more of the vegetable did not significantly affect meal energy intake, whereas substitution of the vegetable for the grain and meat decreased meal energy intake (40 +/- 10 kcal; P < 0.0001). A reduction in vegetable energy density decreased meal energy intake independent of portion size (55 +/- 9 kcal; P < 0.0001). By combining substitution with a reduction in energy density, meal energy intake decreased by 14 +/- 3%.

Conclusions: Serving more vegetables, either by adding more or substituting them for other foods, is an effective strategy to increase vegetable intake at a meal. However, to moderate meal energy intake, vegetables should be low in energy density; furthermore, the substitution of vegetables for more energy-dense foods is more effective than simply adding extra vegetables.

FIGURE 1

Mean (±SE) weight of food consumed according to the portion size of the vegetable served in the addition study (A; n = 49), in which the extra vegetable was added to other meal components, and the substitution study (B; n = 48), in which the extra vegetable was substituted for other meal components. The effects of vegetable portion size were independent of the effects of vegetable energy density in both studies; thus, the values are shown for both energy densities combined. Within each meal component, values with different letters are significantly different (P < 0.0002) as assessed by a mixed linear model with repeated measures.

FIGURE 2

Mean (±SE) energy intake according to the portion size of the vegetable served in the addition study (A; n = 49), in which the extra vegetable was added to other meal components, and the substitution study (B; n = 48), in which the extra vegetable was substituted for other meal components. The effects of vegetable portion size were independent of the effects of vegetable energy density in both studies; thus, the values are shown for both energy densities combined. Within each meal component, values with different letters are significantly different (P < 0.0007) as assessed by a mixed linear model with repeated measures.

FIGURE 3

Mean (±SE) energy intake according to the energy density of the vegetable served in the addition study (A; n = 49) and the substitution study (B; n = 48). The effects of vegetable energy density were independent of the effects of vegetable portion size in both studies; thus, the values are shown for all 3 portions combined. Within each meal component, values with different letters are significantly different (P < 0.0001) as assessed by a mixed linear model with repeated measures.