Although short-term studies have found that serving larger portions of food increases intake in preschool children, it is unknown whether this portion size effect persists over a longer period or whether energy intake is moderated through self-regulation. We tested whether the portion size effect is sustained in preschool children across 5 consecutive days, a period thought to be sufficient for regulatory systems to respond to the overconsumption of energy. With the use of a crossover design, over 2 periods we served the same 5 daily menus to 46 children aged 3–5 y in their childcare centers. In 1 period, all foods and milk were served in baseline portions, and in the other period, all portions were increased by 50%. The served items were weighed to determine intake. Increasing the portion size of all foods and milk by 50% increased daily consumption: weighed intake increased by a mean ± SEM of 143 ± 21 g/d (16%) and energy intake increased by 167 ± 22 kcal/d (18%; both P < 0.0001). The trajectories of intake by weight and energy across the 5-day period were linear and the slopes did not differ between portion conditions (both P > 0.13), indicating that there were sustained increases in intake from larger portions without compensatory changes over time. Children differed in their response to increased portions: those with higher weight status, lower ratings for satiety responsiveness, or higher ratings for food responsiveness had greater increases in intake from larger portions (all P < 0.03). This demonstration that preschool children failed to adjust their intake during prolonged exposure to larger portions challenges the suggestion that their self-regulatory behavior is sufficient to counter perturbations in energy intake. Furthermore, overconsumption from large portions may play a role in the development of overweight and obesity, as the magnitude of the effect was greater in children of higher weight status. This trial was registered at www.clinicaltrials.gov as NCT02963987.

Although dietary guidelines recommend that vegetables and fruits make up half the diet, it is unclear whether serving vegetables and fruits in larger portions will have sustained effects on children's intake over multiple days. This study tested the effects on children's intake of 2 strategies for increasing the proportion of vegetables and fruits: either adding or substituting extra portions as side dishes at meals and snacks over 5 d. In a cluster-randomized crossover design with 3 periods, we provided all meals and snacks for 5 d to 53 children aged 3–5 y in classrooms in their childcare centers. In the Control condition, we served typical portions for all food groups. In the Addition condition we increased portions of low-energy-dense vegetables and fruits by 50%, and in the Substitution condition we increased portions of vegetables and fruits by 50% and also reduced portions of other foods by an equivalent weight. For vegetables, the Addition strategy increased daily intake compared with Control by 24% (mean ± SEM = 12 ± 3 g/d; P = 0.0002), and the Substitution strategy increased intake compared with Control by 41% (22 ± 3 g/d; P < 0.0001). For fruits, consumption increased by similar amounts: Addition by 33% (60 ± 6 g/d) and Substitution by 38% (69 ± 8 g/d; both P < 0.0001). Both strategies increased vegetable and fruit intakes compared with Control across all 5 days (all P < 0.004), although the increase in fruit consumption with Addition declined over time (P < 0.0001). Daily energy intake compared with Control increased by 5% with Addition (57 ± 17 kcal; P = 0.001) but decreased by 6% with Substitution (−64 ± 21 kcal; P = 0.004). Both the Addition and Substitution strategies promoted increases in vegetable and fruit intake over 5 d in preschool children. When excess energy intake is a concern, substituting vegetables and fruits for other foods is a better option than simply serving more. This trial was registered at http://www.clinicaltrials.gov as NCT03242863 (https://clinicaltrials.gov/ct2/show/NCT03242863), where the protocol is available.