How healthy adults determine food portion sizes

Study design: Randomized, controlled, crossover design Test foods: 1. Visual manipulations a. Visible fat – energy-matched butter on toasted French bread b. Visible sugar – energy-matched jam on toasted French bread c. Visible protein – energy-matched ham on toasted French bread d. Visible protein – energy-matched cream cheese on toasted French bread 2. Olfactory manipulations a. Natural odour – plain mashed potato with Italian herbs b. “Fat” odour – herbs + butter or bacon essence added to mashed potato 3. Food form manipulations a. Solid – apple b. Liquid – apple juice Participants will be screened at baseline to confirm eligibility and baseline measurements will be obtained. If qualified, participants will attend eight 45-minute sessions to undergo all study conditions in a random order. Participants will be asked to avoid vigorous activity and drinking alcohol on the previous day, and fast for 10 – 12 hours prior to each session. Participants will arrive at the laboratory between 8am and 9am, and overnight fasting will be verbally confirmed by the researcher. Upon arrival, participants will be asked to drink 200ml of plain water (as a control for thirst and baseline hunger), and baseline appetite ratings will be assessed using validated visual analog scales (VAS) (Flint 2000) 5 minutes after water consumption. Test foods will be presented in large portion sizes (to avoid portion bias and to prevent plate-cleaning), and participants will be asked to take a portion of the test food that is expected to help them achieve a fullness level of 8 out of 10. Participants will also be asked to rate the appearance and intensity of smell of foods. Following that, the portioned food will be removed, and an identical plate of food will be presented to participants again. They will be given 30 minutes to consume the same food until a fullness level of 8 is achieved. After 30 minutes, participants will be asked to rate the palatability of the test foods, how often they will consume the same food again, and VAS again before leaving the lab. Participants will return until all conditions are completed. The washout period between study visits will be at least 24 hours.