12 January - 20 June 2016

Pomegranate juice reduces the glycaemic response of a high glycaemic index food

Researchers from the University of Leeds, have found that pomegranate juice rather than supplements can reduce the glycaemic response of a high glycaemic index food such as bread. Low glycaemic index diets have been shown to have health benefit associated with a reduced risk of developing type 2 diabetes.

Researchers from the University of Leeds, have found that pomegranate juice rather than supplements can reduce the glycaemic response of a high glycaemic index food such as bread.  Low glycaemic index diets have been shown to have health benefit associated with a reduced risk of developing type 2 diabetes. Pomegranates, rich in the polyphenols punicalagin and punicalin have been shown in several human intervention studies to reduce blood pressure and decrease fasting blood insulin. 

In this new study, published in the American Journal of Clinical Nutrition, Kermi et al. tested whether pomegranate polyphenols could lower the glycaemic response of a high-glycaemic index food and looked at the mechanism responsible.  The team carried out two randomised control trials each using 16 healthy volunteers.  For the first trial, the team investigated the effects of pomegranate supplements.  The high dose capsule (400g) contained 2.4 mg punicalin, 48 mg punicalagin, 2.4 mg ellagic acid hexose, 40.2 mg ellagic acid, 3.3 mg glucose and 2.6 mg fructose.  Each participant visited the test centre three times and received 109 g bread with either a placebo capsule, 200 mg placebo and 200 mg pomegranate supplement or 400 g pomegranate supplement with 200 ml water.  The bread was consumed 5 minutes before the supplement. 

For the juice trial, the volunteers visited the test centre 4 times. On 2 visits, they received a control drink containing 10.9 g fructose and 10.3 g glucose dissolved in 200ml to mimic the amount of sugars contained in the pomegranate juice and 109 g bread.  For the other 2 visits, they consumed 200 ml of pure pomegranate juice containing 71.5 mg punicalin, 12.4 mg punicalagin, 2.8 mg ellagic acid hexose, 4.8 mg ellagic acid, 119.1 mg malic acid, 3819 mg citric acid, 10,400 mg glucose and 10,900 mg fructose with 109 g bread. 

For all studies, the meal was consumed within 15 minutes, and blood glucose was measured at 15, 30, 45, 60, 90, 120, 150, and 180 minutes post-consumption.  Kermi et al. also tested the extract on α-amylase in vitro and glucose transport on Caco-2/TC7 cells. 

The study found that pomegranate juice, rich in polyphenols, can reduce the postprandial blood glucose spikes when consumed with bread as a digestible carbohydrate source.  It notes that the effect is quite substantial because the amount of glucose as measured by the area under the curve is reduced by one third with high significance. 

The scientists also tested the effect of an acid solution equivalent to the malic acid, citric acid and potassium content of pomegranate on bread consumption, as previous studies have found that vinegar which is similarly highly acidic reduced the glycaemic response of a bagel by 20%.  However, they report that there was no significant difference when compared to a water control, indicating that the acid content of the pomegranate juice was unlikely to contribute to the effect seen.

Based on in vitro data, they suggest the mechanism of action for these findings is the inhibition of α-amylase by punicalagin, and possibly by the inhibition of glucose transport at low glucose concentration. Kermi et al note that whilst the capsules did not exhibit the same effect as the pomegranate juice they suggest that this could be because of insufficient mixing in the stomach and intestine with the bread. However, they note that under conditions mimicking the stomach the capsule material dissolved in under 5 minutes.  Regarding glucose transport, the authors found that neither pomegranate juice nor its polyphenols affected glucose transport across Caco-2/TC7 cells but they "inhibited uptake of C-glucose into Xenopus oocytes expressing the human glucose transporter type 2". 

RSSL’s can analyse food products for polyphenolic components. To find out more please contact Customer Services telephone 0118 918 4076 or e-mail enquiries@rssl.com

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