Reducing portion sizes, has great potential to reduce food intake and plate waste. At all-you-can-eat buffets people tend to take larger portions of food than they would at home or at a general restaurant. Increased portion sizes can lead to people leaving uneaten food behind – contributing to food-related greenhouse gas emissions. This study develops and evaluates, in two online experiments, a meal guidance intervention to assist consumers with their meal choices. To measure behavioural intentions, we created a simulated buffet scenario where participants see a range of food items (as they would at a buffet) and are then asked to choose which foods and how many portions of each food item they would take. Compared to a control group, offering meal guidance did not appear to significantly decrease the number of grams or calories taken from the simulated buffet. However, there were significant differences in the number of grams and calories taken from the buffet when comparing those who at least followed the guidance in some way, and those who did not. Our research has methodological implications: it presents a novel and easy to implement measure of hypothetical buffet food choices and portioning that can be used in survey experiments. Future research could focus on developing strategies to prompt guests to follow meal guidance.