The past decades showed an increase in the number of meals consumed away from home. Restaurants could therefore play a pivotal role in improve diet quality by offering healthier food on their menus (Glanz and Hoelscher, 2004). One of the instruments that restaurants can use to increase healthier food intake is by making use of portion size. When people are served larger portions, they eat more (Steenhuis & Vermeer, 2009). In this study, we investigate the effectiveness of increased portion sizes of vegetables and lower portion sizes of meat (or fish) in a restaurant setting. Three restaurant locations from a restaurant chain in the Netherlands were selected for a field experiment. A cross-over design was used in which each restaurant was randomly assigned to a sequence of two conditions (i.e., intervention and control condition). In the intervention period, portion sizes of vegetables on plates were doubled (150 grams versus 75 grams) and portion sizes of meat and fish were cut on average with 12.5%. Consumption was calculated by subtracting the residues from the plates from the average served amount. Additionally, p3rticipants received a questionnaire in which a number of questions were asked, i.a., about their satisfaction with the meal and restaurant. In total, 536 participants in the control condition and 470 participants in the experimental condition were obtained. Vegetable consumption was higher in intervention weeks (M = 115.5 grams) than in control weeks (M = 61.7 grams; p < .001). Meat consumption was lower in intervention weeks (M = 183.1 grams) as compared to control weeks (M = 211.1 grams; p < .001). Finally, satisfaction with the restaurant visit did not differ between intervention weeks (M = 4.27) and control weeks (M = 4.35; p > .05). The results are robust given that we found the same effects across the three restaurants. An important implication of this study is that portion sizes could indeed be used as an effective instrument in stimulating healthy consumption behavior without affecting customer’s satisfaction.

• Machiel J. Reinders(Wageningen University and Research Centre, the Netherlands)
• Marlijn Huitink(Vrije Universiteit Amsterdam, the Netherlands)
• Joris Heijnen(Stichting Variatie in de Keuken, the Netherlands)