This is a prospective, double blinded, randomised cross over feeding trial examine high or low FODMAP diet in combination with metformin on postprandial glucose responses and gastrointestinal tolerability and gut microbiota profiles.

The trial will compare high or low FODMAP diet, each of 10 days duration in combination with 5 days metformin, separated by a washout period of at least 2 weeks.

Inclusion Criteria:

1. Age 18-70 years
2. Body mass index 18 to 40 kg/m 2
3. Prediabetes defined as impaired fasting PG 5.6-6.9 mmol/l and/or impaired glucose tolerance with 2-hour PG 7.8-11.1 mmol/l on 75g oral glucose tolerance test (OGTT) and/or HbA1c 5.7-6.4% at screening

Exclusion Criteria:

1. Currently pregnant, lactating, as demonstrated by a positive pregnancy test at screening or planning pregnancy
2. Known current diabetes
3. Current or previous use of glucose-lowering or weight loss drugs in 3 months prior to screening
4. Concurrent participation in other weight loss or lifestyle intervention programmes
5. Current use or recent exposure to any medication that in the opinion of the investigator could have an influence on the patient's ability to participate in this study or on the performance of the test device.
6. Recent intake of prebiotic/probiotic or antibiotic, immunosuppressants (within 8 weeks of randomisation)
7. Extensive skin changes/diseases that preclude wearing the FGM on normal skin at the proposed application sites (e.g., extensive psoriasis, recent burns or severe sunburn, extensive eczema, extensive scarring, extensive tattoos, dermatitis herpetiformis).
8. Known uncontrolled thyrotoxicosis
9. Known vitamin B deficiency
10. Known irritable bowel syndrome or gastrointestinal disorders
11. Estimated glomerular filtration rate (eGFR) <45 ml/min/1.73m2 at screening
12. Current use of steroids
13. Have a known allergy to medical-grade adhesives
14. Known current or recent alcohol or drug abuse
15. Hypersensitivity to metformin
16. Acute or chronic metabolic acidosis, including diabetic ketoacidosis, with or without coma within 3 months of randomisation
17. Currently participating in another investigational study protocol where the testing or results may interfere with study compliance, diagnostic results, or data collection.
18. An identified protected vulnerable patient (including but not limited to those in detention, or a prisoner).
19. Participants who are on a vegetarian or vegan diet as their habitual diet at screening.
20. Participants with clinically significant food allergy to components of the study diet