Alshammari, Norah
(2024)
Enhancing clinical nutrition, glycaemic, appetite and gastrointestinal responses of white rice.
PhD thesis, University of Nottingham.
Abstract
Background: Rice is staple food for over half the world’s population, with approximately 480 million tonnes consumed annually. High consumption of white rice has been linked with high obesity rates and increased risk for type 2 diabetes. Controlling the properties of white rice products (e.g. reducing the glycaemic index (GI) and/or reducing appetite) with relatively simple interventions could contribute to producing foods with health-promoting profiles. One way to reduce the GI of white rice could be through processing. Addition of hydrocolloids has previously been shown to reduce the digestibility of foods.
Hydrocolloids are polysaccharides used to increase viscosity and gelatinization and have many other applications in the food industry. Preliminary in-house data from in vitro studies suggested that the addition of 1% (weight over dry weight of rice) low acyl gellan gum (LAGG) during the cooking of white rice may reduce digestibility rates, though mechanisms are yet to be fully understood.
The overall aim of this project was to investigate for the first time the glycaemic and appetitive response to white rice meal cooked with LAGG in healthy adult participants.
Methods: Firstly, a static in vitro digestion study was undertaken to investigate the effects of adding LAGG to the rice cooking water on starch hydrolysis and GI. A dose response of 0%, 1%, 2% and 3 % LAGG (weight over dry weight of rice) was investigated using a static in vitro digestion model.
Secondly, an acute intervention, randomised, controlled, cross-over trial in 12 healthy participants was carried out. They attended two visits with one week washout having fasted overnight. They were asked to consume a dish of isoenergetic (232 kcal) jasmine white rice meal cooked with and without 3% (weight over dry weight of rice) LAGG and a glass of water. Postprandial blood glucose levels (using the finger prick method), appetite (using visual analogue scales) and gastric appearance and volumes (using magnetic resonance imaging, MRI) were monitored serially for two hours. Following that an ad libitum test meal was offered at lunch and food intake diaries were kept for the remainder of the day.
Lastly, a sustained intervention, randomised, controlled, cross-over trial in 8 healthy participants was carried out. The study consisted in a baseline visit similar to that described above measuring postprandial glucose and appetite responses and lasting for 3.5 hours. The participants were then asked to cook and consume at home the same rice test meal with or without LAGG once daily for 7 days and then returned for another study visit as described above. Food intake diaries and a pedometer tor record step count were provided to record a daily intake for the 7 days’ home intervention. After 3 weeks’ washout period they then returned to repeat the second arm of the study with the other allocated rice meal.
Key Results: The addition of LAGG affected rice starch hydrolysis in the static in vitro model of digestion. 3% LAGG significantly reduced the estimated GI value by 27%, from 94 for the control 0% LAGG, to 69 for the 3% LAGG samples (P < 0.05).
In the acute intervention study all 12 participants completed the protocol. The data showed that the incremental area under the curve (iAUC 2 hours) for blood glucose was significantly different between the meals (P < 0.0001). The composite appetite score AUC 2h was lower for the rice + LAGG meal than for the rice control but the difference was not significant. The MRI images showed that when rice was cooked with LAGG that were multiple rice boluses persisting throughout digestion time and that postprandial gastric volumes were lower compared to rice control though the difference from control was not significant.
In the sustained intervention study all 8 participants completed the protocol. The data confirmed an effect of LAGG in reducing blood glucose response compared to rice control at the baseline study (ANOVA P = 0.0023) and this was maintained after 1 week of sustained intervention (ANOVA P = 0.0440). After one week of eating white rice meal with LAGG the peak glucose value decreased by 1.2 mmol/L compared to the rice control meal (P = 0.0219). Differences in appetite were not statistically significant.
Conclusion
Modifying the cooking process of jasmine white rice with LAGG reduced the estimated in vitro GI of the rice in an in vitro model of digestion and reduced blood glucose responses in healthy humans both after an acute and a sustained intervention. The data are novel and add to knowledge in the field. The modification of the cooking process is safe, simple, and cheap and could potentially provide an intervention to help reduce the post prandial glucose response to white rice, potentially impacting on the rising levels of obesity and type 2 diabetes seen in populations consuming white rice as a staple food.
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