Type 2 Diabetes (T2D) represents a critical public health challenge in Singapore, with prevalence projected to reach one million residents by 2050. This epidemic is largely driven by a distinct "Asian phenotype" characterized by reduced insulin secretion capacity even at lower BMIs and a diet heavily centered on high-glycemic index (GI) white rice. While brown rice offers superior nutritional benefits, its global and local adoption remains low due to entrenched cultural preferences, shorter shelf life, and sensory barriers.

While the link between high-GI carbohydrates and metabolic dysfunction is well-documented, there is limited clinical evidence on the effects of "functional" white rice varieties specifically those engineered to combine low GI properties with significantly enhanced protein content on long-term glycemic control, metabolic and gut microbiome health in Asian populations. The importance of this research lies in its evaluation of a culturally seamless substitution strategy. By replacing conventional white rice with Low-GI (LGI) and High-Protein Low-GI (LGI-HP) varieties, the HARVEST study addresses the metabolic burden of prediabetes without requiring major behavioral shifts. The findings will provide vital mechanistic insights into glucose regulation, insulin sensitivity, and microbial dysbiosis, to provide the evidence based for nutritional strategies for T2D prevention and management.

1. To evaluate the efficacy of a 16-week intervention with functional rice varieties (LGI, LGI-HP) on chronic glycaemic management in Singaporean adults with prediabetes. It is hypothesized that dietary replacement of habitual rice with functional varieties can significantly improve metabolic health compared to the high-GI (HGI) control group
2. To compare the postprandial glucose and insulin responses of LGI, LGI-HP and HGI rice under standardized acute meal testing using continuous glucose monitoring. It is hypothesized that postprandial glucose excursions and glycemic variability will be significantly attenuatated in the functional rice groups compared to the HGI group
3. To characterise longitudinal shifts in gut microbiota composition and identify mechanistic correlations between microbial changes and glucose metabolism. It is hypothesized that long term consumption of functional rice will promote beneficial shift in the gut microbiome which are associated with improved glucose homeostasis.

Inclusion Criteria:

1. Males or females, aged 40 to 65 years old
2. Chinese, Malay or Indian
3. Body Mass Index between 23.0 - 32.0 kg/m2
4. Prediabetes profile as per fasting plasma glucose (≤ 6.9 mmol/L) and HbA1c level (5.7% - 6.4%)
5. Habitually consuming about 3 to 5 servings of polished white rice per day
6. No known food allergies and intolerance to food provided as part of study procedures
7. Proficient in English language
8. Willing to comply to study procedures and provide written consent

Exclusion Criteria:

1. Diagnosed with Type 1 or 2 diabetes mellitus/ OGTT failure during screening visit
2. History or current diagnosis of cardiovascular, endocrine, gastrointestinal, haematological, hepatitis (hepatitis B and C), cancers (except basal cell carcinoma), chronic kidney disease or other medical conditions which may affect study outcomes, as assessed by study team
3. Having chronic medication (eg: metformin, oral corticosteroids etc), and/or supplements that may influence glycaemic management and other study outcomes, as assessed by study team
4. History of bariatric surgery
5. Significant weight change (± 5 % body weight) during the last 3 months
6. Women who are pregnant, breastfeeding or planning pregnancy
7. Drug abuse within the last 5 years
8. Excessive alcohol consumption > 2 servings per day
9. Smoking in the last 1 year
10. Following any special diet(s) which may interfere with study outcomes (eg: Ketogenic diet, intermittent fasting, calorie-deficit)
11. Major change in physical activity and/or dietary habits in the last 3 months
12. Use of oral antibiotics in the last 3 months
13. Participation in other intervention studies, which may affect study outcomes as assessed by study team
14. Staff of IHDP and SIFBI in A*STAR