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

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.