What is the best way to measure what people eat? Comparing self-reported habitual and actual dietary intakes with metabolite markers of dietary intakes.

There are three interventions in the proposed study, each two days long. The first day of each intervention is a standardisation day, the second is a day where all foods of known amounts are provided. For the standardisation days, participants will be instructed to eat, move, and sleep as they normally would, with no extremes in physical activity or other behaviours. This advice will be given for the first day of each of the three interventions. In the morning of each standardisation day participants will start to collect a 24-hour urine sample and complete it the following morning. On each intervention day, participants will provide a fasted blood sample, as well as collect another 24-hour urine sample over the course of the day. Following the blood sample, participants will then present to the metabolic facility to complete a 24-hour recall of food eaten the day before, and eat their breakfast of a prepared food while under observation. Participants will receive and eat all meals (breakfast, lunch, and dinner) in this manner on each intervention day. Meals are prepared and administered by a Dietitian within two-hour windows for each breakfast, lunch, and dinner. On intervention days, participants will be provided with snack foods of known weights to consume outside of the facility if they feel hunger, or wish to eat more. In the morning of the day after each intervention day, participants return any unconsumed snacks, their completed their 24-hour urine samples, provide a fasted blood sample and complete a 24-hour recall. The three interventions will be separated by at least three days washout, so that study requirements are not too onerous on participants. Trial recruitment will be run out of the University of Otago Dunedin campus, in New Zealand. The interventions differ in the food provided each day for meals and snacks. In one intervention: meals will be of whole grains, seafood, and dairy while snacks will be of vegetables, red meat, nuts and seeds. On this day no fruit, chicken, egg, or legumes will be consumed. In a second intervention: meals will be of vegetables, red meat, nuts and seeds while snacks will be of fruit, chicken, egg, and legume. No whole grains, seafood, or dairy will be consumed. In a third intervention: meals will be of fruit, chicken, egg, and legumes while snacks will be of whole grains, seafood, and dairy. No vegetables, red meats, and nuts and seeds will be consumed. The meals provided each day will provide slightly less energy intake (kJ) than participants require each day, to ensure they are consumed in full, with access to the snack foods unrestricted per day to allow participants to eat until full or for other reasons. The purpose of these three interventions is to see how metabolite biomarkers of dietary intakes change in fasted plasma and 24 hour urine in response to foods of known values, as well as compare the metabolite measures with self-reported dietary assessment techniques: a food frequency questionnaire and three 24-hour recalls captured on intervention days.