Does the cost of a meal influence the portion size effect?

Serving larger portions leads to increased intake, but little is known about how the cost of a meal affects this response. Therefore, we tested whether the amount of money paid for a meal influenced the portion size effect at a lunch served in a controlled restaurant-style setting. In a crossover design, 79 adults (55 women; 24 men) came to the lab once a week for 4 weeks to eat a main dish of pasta with side dishes. Across weeks, the meal was varied in two factors: portion size of the main dish (400 g or 600 g) and cost of the meal (US$8 or $16). At discharge subjects completed questionnaires that assessed behaviors thought to influence the response to portion size and cost. Results showed that the portion size of the main dish had a significant effect on meal intake (P < 0.0001). The weight of food consumed at the meal increased by 18 ± 2% (mean ± SEM 83 ± 11 g) and energy intake increased by 20 ± 2% (133 ± 16 kcal) when the larger portion was served. These effects of portion size did not differ across the two levels of cost (both interactions P > 0.37) nor did meal cost have significant effects on meal intake (both P > 0.24). Subject scores for satiety responsiveness did, however, influence the effect of portion size on food intake (P = 0.0007). Serving larger portions led to increased intake in subjects with lower satiety responsiveness scores (P < 0.0001), but did not affect intake in those with higher scores. In summary, the effect of portion size on intake in a restaurant-style setting was not influenced by meal cost but was attenuated in individuals higher in satiety responsiveness.