The study is a parallel, double blind, controlled trial in which study participants will receive a 12-week intervention with 3.6 g/d dried bitter-gourd supplements or a reference intervention with 3.6 g/d dried cucumber supplements. Research subjects will come to the research facility for a test day on four occasions, with an interval of 4 weeks. The main study parameter is fasting levels of plasma glucose.

Bitter gourd (BG) (Momordica charantia) is a highly nutritive vegetable from the cucumber family. The objective is to assess the impact of 12-weeks of BG supplementation on blood glucose levels in subjects with impaired fasting glucose levels. In a previous trial (Bitter-Zoet NL70259.081.19) the short-term effects of BG (4 weeks) were studied, but no effect was observed. In the current trial a different BG cultivar is chosen, the intervention period is prolonged, the dosage per day is higher and study subjects with slightly higher fasting blood glucose levels will be included. The study is a parallel, double blind, controlled trial in which study participants will receive a 12-week intervention with 3.6 g/d dried bitter-gourd supplements or a reference intervention with 3.6 g/d dried cucumber supplements. Research subjects will come to the research facility for a test day on four occasions, with an interval of 4 weeks. The main study parameter is fasting levels of plasma glucose. Secondary outcome measures are glucose tolerance, HbA1c, insulin and HOMA-IR and HOMA-B levels.

Inclusion Criteria:

• age 40-75yrs
• BMI >25 kg/m2
• Having a fasting glucose >6.1 mmol/L

Exclusion Criteria:

• Use of medication/supplements that may influence the study results, such as metformin, gliclazide, glimepiride, tolbutamide, insulin, sitagliptin (DPP4 inhibitor), liraglutide (GLP-1 agonist), acarbose, repaglinide, pioglitazone, corticosteroids (systemically) , SGLT-2 inhibitors, (judged by our research physician)
• Having a fasting glucose >11.0 mmol/L
• History of gastro-intestinal surgery or having (serious) gastro-intestinal complaints
• History of liver dysfunction (cirrhosis, hepatitis) or liver surgery
• Reported slimming, medically prescribed or other extreme diets
• Reported weight loss or weight gain of > 5 kg in the month prior to pre-study screening
• Not willing to give up blood donation during the study
• Current smokers
• Alcohol intake ≥14 glasses (women) or >21 glasses (men) of alcoholic beverages per week, on average
• pregnant or lactating (self-reported)
• Abuse of illicit drugs (soft- and hard drugs)
• Food allergies for products that we use in the study
• Participation in another clinical trial at the same time
• Being an employee of the Food, Health & Consumer Research group of Wageningen Food & Biobased Research or dept. human nutrition and health of Wageningen University.

Supplements will be labeled A and B by a scientist who is not involved in this trial.