Effect of Drinks Containing Fruit Polyphenol Extracts and Fibre on Postprandial Glycaemia. (Glu-MIX)

Intake of carbohydrate-rich foods transiently increases blood glucose levels (known as postprandial glycaemia). Repeated, high, postprandial glucose responses are evidenced to impair pancreatic beta cell function, thus increasing the risk of developing type-2 diabetes mellitus and cardiovascular disease. Therefore, meals that elicit a reduced, or more gradual, rise in blood glucose levels are desirable.

Previous studies have shown that consuming a drink containing fruit polyphenols, such as those from blackcurrants (BC), immediately before a high carbohydrate meal, reduced the postprandial glycaemic response. Importantly, other fruit components, namely soluble fibres, also impact on carbohydrate digestion by slowing gastric emptying rates. It is not yet known the effect of combining fibre and polyphenols on postprandial glycaemia. Although limited, there is a growing body of evidence showing beneficial acute effects of polyphenols in cognitive function which is of great interest in many work and academic environments where fast cognitive enhancement is wanted to perform a task or an exam.

This study will investigate the effects of drinks containing BC polyphenol extract combined with pulp (source of fibre), and pulp alone, on postprandial outcomes and cognitive function following a mixed carbohydrate (starch and sucrose) test meal.

Study design: A randomised, controlled, double-blind, cross-over study, of the healthy adult UK population, will be conducted. All subjects will receive the placebo drink, pulp only drink and the pulp with polyphenol drink in a random order. Baseline (fasted) blood samples will be taken before consuming the test drink (T0 min). Immediately following consumption of the drink, a mixed carbohydrate test meal will be consumed. Further blood samples will be collected at regular times until T150 min. Blood samples will be analysed for plasma glucose, insulin, glucose-dependent insulinotropic peptide (GIP) and C-peptide. Subjects will also perform a 30 min computer based cognitive performance test at baseline (T-45 min) and endpoint (T165 min). Visual analogue scales will be used to assess the effect of the test drinks on a range of sensory characteristics e.g. palatability, satiety and subjective mood feelings. Finally, an ad libitum pasta meal at the end of the study visit (T 215 min) will be used to assess the effects on energy intake.

• Placebo (Dietary supplement): Drinks will be delivered in random order at 3 separate study visits immediately before a high carbohydrate meal. A minimum of 4 days (ideally 7 days) wash-out period will be required between study days.
• Polyphenol and fibre (Dietary supplement): Drinks will be delivered in random order at 3 separate study visits immediately before a high carbohydrate meal. A minimum of 4 days (ideally 7 days) wash-out period will be required between study days.
• Fibre (Dietary supplement): Drinks will be delivered in random order at 3 separate study visits immediately before a high carbohydrate meal. A minimum of 4 days (ideally 7 days) wash-out period will be required between study days.

Primary outcomes

• Postprandial glycaemia (iAUC 0-30 min) [30 min]: The primary endpoint is iAUC 0-30 min for plasma glucose concentrations

Secondary outcomes

• Postprandial glycaemia: iAUC 0-120 min [120 min]: iAUC 0-120 min for plasma glucose concentrations
• Postprandial glycaemia: iAUC 0-150 min [150 min]: iAUC 0-150 min for plasma glucose concentrations
• Postprandial glycaemia: iCmax [150 min]: iCmax for plasma glucose concentrations
• Postprandial glycaemia: Tmax [150 min]: Tmax for plasma glucose concentrations
• Postprandial glycaemia: absolute concentrations at specific time points [150 min]: Absolute concentrations at specific time points, for plasma glucose concentrations
• Postprandial insulinemia: iAUC 0-30 min [30 min]: iAUC 0-30 min for serum insulin concentrations
• Postprandial insulinemia: iAUC 0-120 min [120 min]: iAUC 0-120 min for serum insulin concentrations
• Postprandial insulinemia: iAUC 0-150 min [150 min]: iAUC 0-150 min for serum insulin concentrations
• Postprandial insulinemia: iCmax [150 min]: iCmax, for serum insulin concentrations
• Postprandial insulinemia: Tmax [150 min]: Tmax for serum insulin concentrations
• Postprandial insulinemia: absolute concentrations at specific time points [150 min]: Absolute concentrations at specific time points, for serum insulin concentrations
• Postprandial C-peptide: iAUC 0-30 min [30 min]: iAUC 0-30 min for plasma C-peptide concentrations
• Postprandial C-peptide: iAUC 0-120 min [120 min]: iAUC 0-120 min for plasma C-peptide concentrations
• Postprandial C-peptide: iAUC 0-150 min [150 min]: iAUC 0-150 min for plasma C-peptide concentrations
• Postprandial C-peptide: iCmax [150 min]: iCmax for plasma C-peptide concentrations
• Postprandial C-peptide: Tmax [150 min]: Tmax for plasma C-peptide concentrations
• Postprandial C-peptide: Absolute concentrations at specific time points [150 min]: Absolute concentrations at specific time points, for plasma C-peptide concentrations
• Postprandial blood glucose-dependent insulinotropic peptide (GIP): iAUC 0-30 min [30 min]: iAUC 0-30 min for plasma GIP concentrations
• Postprandial blood glucose-dependent insulinotropic peptide (GIP): iAUC 0-120 min [120 min]: iAUC 0-120 min for plasma GIP concentrations
• Postprandial blood glucose-dependent insulinotropic peptide (GIP): iAUC 0-150 min [150 min]: iAUC 0-150 min for plasma GIP concentrations
• Postprandial blood glucose-dependent insulinotropic peptide (GIP): iCmax [150 min]: iCmax, for plasma GIP concentrations
• Postprandial blood glucose-dependent insulinotropic peptide (GIP): Tmax [150 min]: Tmax for plasma GIP concentrations
• Postprandial blood glucose-dependent insulinotropic peptide (GIP): Absolute concentrations at specific time points [150 min]: Absolute concentrations at specific time points, for plasma GIP concentrations
• Cognitive function test scores [Before and after 150 min blood collection]: Descriptive statistics

Other outcomes

• 7-d food diary (estimated/unweighed) [7-days]: Habitual dietary intake analysis
• 100 mm visual analogue scale (VAS) measures of the palatability of the study drink [10 min following the test drink]: For each VAS, a numerical score between 0 (not at all) and 100 (extremely) mm was obtained.
• 100 mm visual analogue scale (VAS) measures of mood, satiety and digestive comfort [150 min]: For each VAS, a numerical score between 0 (not at all) and 100 (extremely) mm was obtained.
• Ad libitum energy intake [15 min]: Energy intake during ad libitum meal
• 100 mm visual analogue scale (VAS) measures of the palatability of the ad libitum meal [15 min following the ad libitum meal]: For each VAS, a numerical score between 0 (not at all) and 100 (extremely) mm was obtained.
• Buccal mouth swab [One off sample, collected at the first 1 day of study visit]: Future exploratory analysis of lactase activity via the derived allele at the European

Sex: All, ages: 18 Years to 70 Years, accepts healthy volunteers

Inclusion Criteria:

* Age: 18-70 years
* Men and women
* Healthy (free of diagnosed diseases listed in the exclusion criteria)
* Body Mass Index 18-35 kg/m2
* Able to understand the information sheet and willing to comply with study protocol
* Able to give informed written consent

Exclusion Criteria:

* Those diagnosed with Phenylketonuria (PKU)
* Those with known or suspected food intolerances, allergies or hypersensitivity
* Women who are known to be pregnant or who are intending to become pregnant over the course of the study
* Women who are breastfeeding
* Participation in another clinical trial
* Those who have donated blood within 3 months of the screening visit and participants for whom participation in this study would result in having donated more than 1500 millilitres of blood in the previous 12 months.
* Full Blood Counts and Liver Function test results outside of the normal range.
* Current smokers, or reported giving up smoking within the last 6 months
* History of substance abuse or alcoholism
* Reported history of Cardiovascular disease, diabetes (or fasting glucose ≥ 7.1 mmol/L), cancer, kidney, liver or bowel disease, gastrointestinal disorder or use of drug likely to alter gastrointestinal function
* Unwilling to restrict consumption of specified high polyphenol/ high fibre foods for 48 h before the study
* Weight change >3 kg in preceding 2 months
* Blood pressure ≥160/100 mmHg
* Total cholesterol ≥ 7.5 mmol/L; fasting triacylglycerol concentrations ≥ 5.0 mmol/L
* Medications that may interfere with the study: alpha-glucosidase inhibitors (acarbose: Glucobay), insulin sensitizing drugs (metformin: Glucophage, Glucophage SR, Eucreas, Janumet; thiazolidinediones: Actos, Competact), sulfonylureas (Daonil, Diamicron, Diamicron MR, Glibenese, Minodiab, Amaryl Tolbutamide), and lipid lowering drugs (statins, nicotinic acid, colestyramine anhydrous, ezetimibe, fibrates). Other medications should be reviewed by medical representative from KCL on a case by case basis.
* Nutritional supplements that may interfere with the study: higher dose vitamins/minerals (>200% Recommend Nutrient Intake), B vitamins, Vitamin C, calcium, copper, chromium, iodine, iron, magnesium, manganese, phosphorus, potassium and zinc. Subjects already taking vitamin or minerals at a dose around 100% or less up to 200% of the RNI, or evening primrose/algal/fish oil supplements will be asked to maintain habitual intake patterns, ensuring that they take them every day and not sporadically. They will be advised not to stop taking supplements or start taking new supplements during the course of the study.

• Castro-Acosta ML, Smith L, Miller RJ, McCarthy DI, Farrimond JA, Hall WL. Drinks containing anthocyanin-rich blackcurrant extract decrease postprandial blood glucose, insulin and incretin concentrations. J Nutr Biochem. 2016 Dec;38:154-161. doi: 10.1016/j.jnutbio.2016.09.002. Epub 2016 Sep 14. PMID 27764725
• Results publication: Pinto AM, Hobden MR, Brown KD, Farrimond J, Targett D, Corpe CP, Ellis PR, Todorova Y, Socha K, Bahsoon S, Haworth C, Marcel M, Nie X, Hall WL. Acute effects of drinks containing blackcurrant and citrus (poly)phenols and dietary fibre on postprandial glycaemia, gut hormones, cognitive function and appetite in healthy adults: two randomised controlled trials. Food Funct. 2023 Nov 13;14(22):10163-10176. doi: 10.1039/d3fo03085g. PMID 37902089

• Wendy L Hall, PhD, Principal investigator, King's College London