Flour particle size of breads and blood glucose and insulin response

This study is a randomised crossover design to measure the blood glucose and insulin responses to breads made with different grain particle size and fibre content. It will be conducted in a research clinic at the University of Otago. The study includes three bread exposures: (1) A bread made with finely milled wholegrain flour providing 50 g available carbohydrate (approximately four to five slices), served with 250 mL water (2) A bread made with coarse stoneground wholegrain flour providing 50 g available carbohydrate (approximately four to five slices), served with 250 mL water (3) A bread made with fine stoneground wholegrain flour providing 50 g available carbohydrate (approximately four to five slices), served with 250 mL water Each bread is matched for all macronutrients. They differ in the particle size and the structure of the grain. Each bread will provide 50 g available carbohydrate. Intervention order will be randomised for the four breads. Participants will be able to select the days they wish to attend the clinic for. All treatments will be administered within a 6 week period, with a minimum washout of one day between each treatment. Key measures: (1) Blood glucose will be measured via capillary blood taken from a finger prick. (2) Insulin will be measured via venous blood taken from a cannula placed into a vein in the forearm Participants will arrive at the research clinic between 7:00 AM and 7:30 AM, having completed a water-only fast for a minimum of 10 hours. A text reminder will be sent to participants 24 hours before, to remind them to adhere to fasting conditions, and to keep their exercise and evening meal consistent before testing mornings. Participants will have been provided with a food and exercise diary to complete for the 24 hours prior to testing. Upon arrival, participants will be fitted with a cannula into a vein in the forearm. This will be performed by a trained health professional (nurse or doctor). They will be given a brief questionnaire to fill out which checks adherence to the study conditions. They will be required to be seated for a minimum of 10 minutes prior to their first (baseline) blood measurements being taken. Two capillary blood samples will be taken (via fingerprick) to assess baseline (fasted) blood glucose, and a 2 mL venous blood sample will be drawn from the cannula to measure insulin at baseline. Participants will be instructed to consume their test food within 10 minutes, alongside 250 mL water. At 15 minutes following the commencement of eating, a fingerprick blood sample will be taken to measure blood glucose, and a 2 mL sample of venous blood will be drawn from the cannula to measure insulin. These blood samples will be repeated at 30, 45, 60, 90, 120, 150, and 180 minutes. At the end of the 3 hour testing session, participants will be offered a small snack to take away with them. Each morning of testing will take approximately 3.5 hours of participants' time. The total amount of blood collected each day will be 16 mL. During the 3-hour testing time, participants will remain seated, except for a bathroom break which will be scheduled at 2 hours post-meal. Participants will be free to take additional bathroom breaks if they require. The research will be delivered by Evelyn Mete (PhD Student and New Zealand Registered Dietitian), alongside a supervisory team who have many years' experience delivering similar trials.