Effect of low vs high glycaemic index diet on day-long glycaemia in healthy adults

INTERVENTION: Two different study diets are provided i.e. low glycemic index (LGI) and high glycemic index (HGI). The subjects will be randomized to start the trial with one of the two study diets for 5 days. After that the subjects will have a 3‐day wash‐out period, and then they will be switched to the other diet for another 5 days. The details of the 2 study diets are as follows: Study diets We will use a meal‐delivery service Eatology (http://www.eatologyasia.com) which allows customization of the foods to provide all foods during the study period. A sample 5‐day menu is attached as appendix. We will discuss with their team to come up with meals and snacks that conforms to the following specifications, that are delicious and attractive: Table 1 – Nutritional composition of the study diets ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ Parameter LGI diet HGI diet Energy (kcal/d) 1600 (F) – 2000 (M) 1600 (F) – 2000 (M) Protein (%kcal) 25 25 Carbohydrates (%kcal) 50 50 Total fats (& saturated fats) (%kcal) 25 (10) 25 (10) Fibre (g/1000kcal) 15 15 Dietary GI 40‐45 60‐65 Dietary Glycemic Load (GL) 110‐120 150‐170 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ F‐ Female, M – Male. These are approximations only. Two versions of each study diet will be formulated, one western‐style and one Asian‐style to cater for individual preference. The diets will be designed to be matched for macronutrient and fibre for each meal and the whole day, with a 15‐25 units difference in dietary GI (i.e. the weighted average GI of all foods consumed by the carbohydrate contribution), and 40‐50 units difference in dietary glycemic load (GL) (i.e. the sum of the GL from all foods). Only foods with a tested GI in the international GI database (Atkinson et al. Diabetes Care. 2010) will be used in the design of the study diets to ensure accuracy of the dietary GI which is calculated using the following formula: Dietary GL * 100 / total available carbohydrates (in grams). The study foods will be delivered to the subjects’ home or office address daily, with instructions on how to store, reheat and prepare the foods properly. In the evening of the run‐in period, the research assistant will insert the FreeStyle CGMS sensor into the upper arm of the subject and calibrate the reader for use. Each FreeStyle CGMS sensor can last 14‐days, will automatically sample blood glucose data every 15‐minutes, and can store up to 8‐hours’ worth of data since the last scan. Subjects will be educated on how to scan the sensor for data, and indicate their meal‐time using the inbuilt function of the reader. They will be instructed to scan for data every 6‐7 hours during the time they are awake to avoid loss of data. CONDITION: Postprandial blood glucose INCLUSION CRITERIA: 1. Aged between 18 – 40 years 2. Body mass index between 18.5 – 23 kg/m2 3. Non‐smoking 4. Non‐regular alcohol drinker 5. Generally healthy with no chronic disease (including type 2 diabetes) 6. No skin sensitivity issues 7. Able to wear the subcutaneous CGMS sensor for 14 days 8. Able to receive, store and reheat the study meals according to the instructions 9. No special dietary requirement including vegetarianism and veganism After a 1‐day run‐in period, the subjects will be randomized to start the trial with one of the two study diets for 5 days. Then they will have a 3‐day wash‐out period before being switched to the other diet for another 5 days. The compositions of the diets are given in the next sub‐section. All foods and drinks during the intervention periods (i.e. 2 × 5 days) will be provided, while the subjects are allowed to resume their normal diet during the run‐in and wash‐out period. Subjects will be instructed to eat only foods provided by the researchers through the meal‐delivery service, and take and send photos before and after their meal for assessment of compliance. Subjects will be given a list of beverages they could consume which is appropriate for their assigned diet (for example, watermelon juice for HGI; most fruit juices other than watermelon juice for LGI. Water and sugar‐free soft drinks are considered acceptable for both diets) . The subjects are required to take and send photos of all the drinks they taken. PRIMARY OUTCOME: Day‐long glycaemia (as indicated by the AUC of glucose from the time the subject wakes up until he/she goes to sleep at night); Hyperglycaemic index, defined as the AUCglucose above 6.0 mmol/L divided by the total time of the observation period (i.e. 24 hours). SECONDARY OUTCOME: A 5‐point Likert scale will be given to the subjects to assess the subjects’ like or dislikes of the diet Mean amplitude of glycaemic excursion, which takes into account the glycaemic peaks and nadirs encountered during a day, beyond average glucose values, will be calculated using the standard formula (Diabetes Care. 2011 May; 34(Suppl 2): S120–S127) Peak blood glucose at each meal derived from the record of FreeStyle CGMS sensors Postprandial glycaemia (as indicated by the iAUC of glucose) 10. Ownership of a smartphone with camera function