The effect of prolonged dietary exposure and the association between taste receptor expression, fatty acid taste sensitivity and satiety in healthy weight participants

Subjects will participate in a crossover dietary intervention, involving consumption of both a high and low fat diet for a period of 10 weeks each, with a two week wash out period. The high fat diet will consist of 40% fat while participants on the low fat diet will be asked to consume <20% fat. To account for differences in energy needs, all diets will be customised to each participant. For the high fat diet, participants will be provided with a number of high fat foods (i.e. full cream milk, cooking oil, butter, cheese, chocolate bars, nuts, avocado, muffins etc) on a weekly basis and will be supplied with an information sheet detailing which foods to consume and how many portions of each (i.e. 250g toasted muesli and 1 chocolate bar). Participants on the low fat diet will be instructed to limit their dietary fat consumption to <20% total energy. Participants will be provided with nutritional advice and an information package to assist with compliance of the diet. Participants will be asked to swap high fat foods for low fat alternatives (e.g. full-fat dairy for low fat dairy and high fat salad dressing for low fat salad dressing) and discontinue the use of oil, butter and other cooking fats. Participants will also be asked not to consume other sources of fats including nuts, avocado, take away food (pizza, burgers, hot chips), processed meat or meat with visible fat or snack foods such as chocolate or potato chips. The diet will also supplemented with additional foods such as low fat, portion controlled meals which the participant will be allowed to consume for either lunch or dinner. A low fat recipe booklet will also be provided to assist with food preparation. To assess dietary adherence, weekly 24-hour food records will be completed. A number of measures will also be taken prior to, during and following the intervention to evaluate the effect of dietary fat intake on fatty acid taste sensitivity, taste receptor expression and corresponding satiety responses. In one session, fatty acid taste sensitivity will be measured using milk samples with added oleic acid (and control samples with no added oleic acid) using a three-alternate forced choice sensory procedure. Putative fatty acid taste receptor expression (GPR120, GPR40 and CD36) will be measured by collecting a microgram quantity of taste cells in saliva samples. The procedure will involve participants running their teeth along the front of the tongue (fungiform papillae) with sufficient pressure and will be asked to expectorate into a tube until approximately 1mL of saliva is collected. RNA level will be measured using real time PCR techniques. Participants will also perform a fat ranking task using custard samples varying in fat percentage (0, 2, 6 and 10%) to assess fat perception and rate liking of various high and low fat foods. Height, weight, hip and waist circumference will be measured. Within 7 days, participants will be provided with, and asked to consume a standardised breakfast (approximately 1200kJ consisting of cereal, milk, yoghurt, fruit and tea/coffee) on the morning of testing. Participants will rate appetite, prospective food consumption and hunger perceptions on a 100mm visual analogue scale before and after consumption of the breakfast. Three hours later, participants will return to the sensory laboratory where food consumption will be measured. Participants will be presented with a buffet style lunch, with foods presented in excess (10,000kJ) and asked to eat until comfortably full. The amount of food consumed will be calculated by weighing the meal prior to, and following consumption (in grams). Energy intake will also be calculated. Participants will again rate appetite perceptions using the satiety questionnaire.