The study is a randomized, cross-over, double blind, controlled trial in which study participants will receive two 4-week interventions with a washout period of 4 weeks between interventions. Study subjects will visit the research facility before and after each intervention period for a test day. In the third intervention week participants are provided with a 3-day controlled diet and glucose responses will be monitored via a continuous glucose monitoring device.

Bitter gourd (BG) (Momordica charantia), is a highly nutritive vegetable from the cucumber family. The objective is to assess the impact of 4-week BG supplementation on blood glucose levels and glucose tolerance in subjects with an impaired fasting glucose or with an impaired glucose tolerance and to evaluate how BG supplements modulate glucose response curves during meal intake. The study is a randomized, cross-over, double blind, controlled trial in which study participants will receive two 4-week interventions with a washout period of 4 weeks between interventions. Study subjects will visit the research facility before and after each intervention period for a test day. In the third intervention week participants are provided with a 3-day controlled diet and glucose responses will be monitored via a continuous glucose monitoring device. The intervention will be a 4-week intervention with 2.4g/d dried bitter-gourd supplements and a reference intervention with 2.4g/d dried cucumber supplements. The main study parameter is fasting levels of plasma glucose and 2hour plasma glucose after a 75-gram OGTT.

Inclusion Criteria:

• age 50-75yrs

• BMI >25 kg/m2

• Having veins suitable for blood sampling via a catheter

• Having one or more of the following criteria:

  • HbA1c > 5.7%
  • fasting glucose >5.6mmol/L
  • two-hour glucose levels >7.8 mmol/L on the 75-g oral glucose tolerance test .

Exclusion Criteria:

• History of gastro-intestinal surgery or having (serious) gastro-intestinal complaints
• History of liver dysfunction (cirrhosis, hepatitis) or liver surgery
• Kidney dysfunction (self-reported)
• Use of medication/supplements that may influence the study results, such as medicines known to interfere with glucose homeostasis.
• Anaemia (Hb values <7.5 for women and <8.5 for men)
• 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 ≥4 glasses of alcoholic beverages per day
• Abuse of illicit 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.