Acute Effects of Blackcurrant and Citrus Polyphenol Extracts on Postprandial Glycaemia
Condition: Postprandial Period
Study type: Interventional

Summary: 
      Large postprandial glucose responses are associated with increased risk of chronic diseases,
      including diabetes and cardiovascular disease. Our group have previously shown that fruit
      polyphenol extracts, when consumed immediately before a mixed carbohydrate meal, reduce
      postprandial glycaemia. The aim of this study is to investigate the effects of a blackcurrant
      polyphenol extract and citrus polyphenol extract (and their combination), on postprandial
      glycaemia, insulinaemia and gastrointestinal hormone concentrations following a mixed
      carbohydrate test meal. It is hypothesised that blackcurrant and citrus extracts alone will
      inhibit glycaemia compared to placebo, and a combination of the two will have a greater
      effect.
    

Detailed description: 
      Intake of carbohydrate-rich foods transiently increases blood glucose levels (known as
      postprandial glycaemia). Repeated high postprandial glucose responses are evidenced to
      dysregulate functional proteins, oxidative stress and pancreatic beta cell function; thus
      increasing the risk of diabetes and cardiovascular disease. Accordingly, meals that elicit a
      reduced, or more gradual, rise in blood glucose levels are desirable. Fruit polyphenols may
      help to limit the glucose excursion following a high carbohydrate meal. Previous research by
      our group has demonstrated that blackcurrant polyphenols significantly inhibited the average
      incremental area under the curve (T+0 to +30 min) of plasma glucose. Possible mechanisms
      include inhibition of intestinal enzymes and inhibition of intestinal glucose absorption by
      decreasing Sodium-glucose linked transporter 1 (SGLT-1) / Glucose transporter 2 (GLUT-2)
      glucose transporter activity. In vitro data suggests that citrus polyphenols may impact on
      carbohydrate metabolism by binding to starch molecules, however, effects on postprandial
      glycaemia are not yet known. Blackcurrants and citrus fruits have distinct polyphenol
      profiles and may therefore act on glucose homeostasis via different mechanisms. Blackcurrants
      are rich in anthocyanins and flavanols, whereas citrus fruits are rich in flavanones,
      hesperetin and naringenin. Theoretically, combining blackcurrant with citrus extracts may
      have synergistic effects.

      The aim of this study is to investigate the effects of blackcurrant polyphenol extracts and
      citrus polyphenol extracts (and their combination), on postprandial glycaemia, insulinaemia
      and gastrointestinal hormone concentrations following a mixed carbohydrate test meal. It is
      hypothesised that blackcurrant and citrus extracts alone will inhibit glycaemia compared to
      placebo, a combination of the two will have a greater effect.

      Study design: A randomised, controlled, double-blind, cross-over study will be conducted.
      Subjects will consume different drinks at 4 separate study visits. Drinks will contain
      either: blackcurrant extract (low dose), blackcurrant extract (high dose), citrus extract
      (low dose), blackcurrant and citrus extract (low dose + low dose), or placebo (no
      polyphenols). The study will utilise an incomplete block design. Subjects will consume the
      placebo drink and 3 out of 4 of the polyphenol-containing drinks during the study. At least a
      7-day wash-out period will be required between study days. Baseline (fasted) blood samples
      will be taken in duplicate at T-10 min and T-5 min before consuming the test drink (T+0 min).
      Immediately following consumption of the drink, a mixed carbohydrate test meal will be
      consumed. Further blood samples will be collected at 10 min intervals for the first 30 min
      and then every 15 min until T+90 min and at T+120 min. Blood samples will be analysed for
      plasma glucose, insulin, glucose-dependent insulinotropic peptide (GIP), glucagon-like
      peptide 1 (GLP-1), peptide YY (PYY), C-peptide and nonesterified fatty acids (NEFA).
    

Intervention name(s): Blackcurrant extract (low dose); Placebo; Citrus extract (low dose); Blackcurrant extract (high dose); Blackcurrant and citrus extracts (low dose / low dose)
Intervention type(s): Dietary Supplement; Dietary Supplement; Dietary Supplement; Dietary Supplement; Dietary Supplement
Intervention description(s): Participants will consume a small beverage that contains blackcurrant extract (low dose) immediately before a high-carbohydrate meal.; Participants will consume a small beverage that contains no fruit extracts immediately before a high-carbohydrate meal.; Participants will consume a small beverage that contains citrus extract (low dose) immediately before a high-carbohydrate meal.; Participants will consume a small beverage that contains blackcurrant extract (high dose) immediately before a high-carbohydrate meal.; Participants will consume a small beverage that contains blackcurrant and citrus extracts (low dose / low dose)immediately before a high-carbohydrate meal.
Allocation: Randomized
Intervention model: Crossover Assignment
Intervention model description: Incomplete block cross-over design. Each participant receives placebo plus 3 out of 4 active treatments.
Masking: Double (Participant, Investigator)
Primary purpose: Prevention
Keywords: Blackcurrant; Citrus; Polyphenols; Glucose; Postprandial; Metabolism