Susceptibility to Weight Gain: Studies of Appetite Regulation in Lean, Overweight & Obese Men & Women

The aims of the study are to identify eating & appetite behaviours which characterise people who may be susceptible to over-consumption, weight gain and obesity, by: (i) the use of eating behaviour questionnaires & (ii) investigating individuals responses to a range of dietary challenges which vary in energy, fat, carbohydrate & protein content. There will be 5 visits to the Human Nutrition Unit appetite centre. One brief screening visit [Phase 1] (approx 40 min) plus 4 x 1 day study visits [Phase 2]. Visit 1 = Phase 1 characterization visit. This is a screening visit where volunteers will be consented and registered. At this visit subjects will complete a collection of screening questionnaires to complete the characterization phase of the study. Visits 2-5 = Phase 2 intervention study visits. Once volunteers have completed the first phase of the study, they will come into the Human Nutrition Unit appetite centre fasted (=nothing to eat) on 4 additional separate days, arriving in the early morning (8am) and staying until the early afternoon (13:30pm). The trial design will be a 4 treatment cross-over, single day intervention study comprising 100 healthy lean, overweight & obese male & female subjects (aged 18-60 years). Participants will be given either a high fat, low fat, high energy or low energy test breakfast followed by an ad libitum lunch meal 3.5 hours later. There will be a minimum washout period of 7 days in between treatments. Each participant will complete all study arms of phase 2 in a randomized order according to a Latin square design. The 4 interventions are: A.High fat breakfast (2.5MJ; 50%en fat), followed by an ad libitum lunch meal. B.Low fat breakfast (2.5MJ; 25%en fat), followed by an ad libitum lunch meal C.High energy (2.5MJ; 37.5%en fat) breakfast, followed by an ad libitum lunch meal D.Low energy (0.5.MJ; 37.5%enfat ) breakfast, followed by an ad libitum lunch meal [MJ = mega joules; %en fat = the percent of the treatments energy contributed by fat] The breakfast meals will comprise typical breakfast food items consumed in New Zealand including toast with butter & jam & scrambled eggs. All breakfast items provided must be consumed by participants. The ad libitum lunch will comprise of a lamb casserole & rice. The lunch meal will provide items served in moderate excess and participants will be instructed to eat as much of all food items available until they feel comfortably full.