Effects of high amylose wheat flour on the metabolic health of healthy Australian adults

The dietary intervention trial will use a controlled, completely randomised crossover design and comprise seven dietary treatments (glucose reference drinks completed on 3 occasions and four different types of bread). The four bread types include 1 wholemeal flour using conventional wheat, 1 refined flour using conventional wheat, 1 wholemeal flour using high amylose wheat, 1 refined flour using high amylose wheat. The nutrient composition of the breads are based on standard wholemeal and white breads that are commercially available. The trial will run for approximately 8 weeks and will involve 7 clinic visits that are approx. 4 hours duration. Each participant will consume the 4 different types of bread and the control glucose drink (completed on 3 occasions) with a total of 7 days of testing, approximately 1 week apart. The amount of each bread type and glucose drink will equate to 50 g of carbohydrate. The order in which the 4 breads and 3 glucose drinks are to be consumed will be randomised across the 7 visits. Prior to each clinic visit, participants will be asked to avoid eating foods high in fibre, avoid heavy exercise and avoid consuming alcohol 24 hours prior. Participants will fast (no food or drinks except water) for 12 hours prior to each visit. Upon arrival at the clinic participants will have their height and weight measured and an initial finger prick blood sample will be taken to ensure blood glucose level is below 5.5mM before a cannula is inserted into the forearm for a baseline blood sample. Participants will then consume the bread or glucose drink and subsequent blood samples will be collected at 15, 30, 45, 60, 90,120, 150, 180 minutes. Cannula insertion for blood sampling will occur at each study visit, amounting to a total of 9 blood draws and an overall total of 55ml (about 3 tablespoons full) per visit. The cannula remains in place for 3 hours and is removed after the last blood sample. Participants will complete a visual analogue scale to measure satiety at time point 0 and every 30 minutes up to 180 minutes. Six of 20 participants will be randomly selected to also provide hourly breath samples so that breath hydrogen can be determined using a Gastrolyser. Breath hydrogen will be measured at 30 minute intervals during the blood sampling period. Once the last blood sample is collected at 3 hr, participants will take the portable Gastrolyser with them and continue to measure the breath hydrogen levels at 30 min intervals for a further 9 hr (total 12 hr).