Large portions contribute to excess consumption. We tested whether a portion size labeling intervention influenced consumers to select smaller lunch portions. Two cafés introduced a reduced-sized main course (half the original size and ∼30% lower in price), January-May 2024. Cafés were randomized to a portion labeling intervention or control. During the baseline and follow-up periods, the reduced size was called "Small" and the original "Large" in both cafés. During the intervention period, labels remained unchanged in the control; the intervention café relabeled the reduced size "Standard" and retained "Large" for the original size. The primary outcome was average kcal per main course purchased. Secondary outcomes were: 1) average kcal per transaction; 2) number of main courses purchased; and 3) gross sales. We also examined whether introducing a reduced-sized main course irrespective of the labeling intervention was associated with 1) average kcal per transaction, and 2) sales during the study compared to 2023. Cafés sold 2940 reduced-sized and 8587 original-sized main courses. Average kcal per main course purchased (DID -7. 5 kcal 95%CI: 25. 8, 10. 7) and kcal per transaction (DID -21. 6 kcal 95%CI: 46. 6, 3. 3) did not significantly differ compared to the control during the intervention. Regardless of portion labels, transactions with a reduced-sized vs. original-sized main course had 405 fewer kcal (95%CI: 414. 7, -396. 1). Average weekly gross sales increased by 3131 (95%CI: 2, 098, 4164) in 2024 vs. 2023. The labeling intervention did not reduce kcal purchased, but offering reduced sizes regardless of labeling lowered kcal per transaction and did not harm sales.
Hua et al. (Fri,) studied this question.