Evidence from the nutritional literature suggests that berry consumption is associated with improvements in glycaemic control. A number of studies have looked at berry consumption (here) and concluded that berries are beneficial at modulating postprandial blood sugar levels. The reason for the beneficial effects of berries is not known, but may relate to the presence of particular flavonoids concentrated in the berries skin that inhibit the transporters responsible for sugar absorption. Studies also suggests that the fibre content of berries may play a role in the beneficial glycaemic effects, although this is not clear. In addition, natural sugars in the berries have been suggested to inhibit the absorption of other dietary sugars due to competition for enzymes and transporters. Of course, the fibre, sugar and flavonoid content of berries may all contribute to the beneficial effects. In addition, research has highlighted that the beneficial effects of berries may be more pronounced in those with blood sugar irregularities.
For example, in one study1 researchers tested the ability of sea buckthorn berries, sea buckthorn oil, an extract of phenolic from sea buckthorn berries, or frozen bilberries to improve metabolic function in two groups of overweight female subjects. One group of subjects had a cardiometabolic profile that put them at increased risk of developing the metabolic syndrome compared to the other group. The effects of the treatments were subtle but clear trends were evident from the results. In particular, sea buckthorn berries caused a reduction in the concentrations of low density lipoprotein (LDL) and very low density lipoproteins (VLDL) in those women at high risk of metabolic syndrome. Sea buckthorn oil caused a trend of decreased total, intermediate-density lipoprotein (IDL) and LDL in those women at an increased risk of metabolic syndrome. Bilberries also caused beneficial changes in serum lipids and lipoproteins but in the women not at risk of metabolic syndrome circulating levels of VLDL were observed.
These results suggest that berries have favourable effects on the risk factors associated with metabolic syndrome. The beneficial effects on lipoprotein metabolism may relate to improvements in postprandial glycaemia. A high glycaemic response to carbohydrates, as is common in refined grains, overloads the liver with nutrients and this increases the production of fatty acids. These fatty acids can cause metabolic dysfunction which ultimately affects lipoprotein metabolism. The authors suggest that there was no real explanation for the negative effects of whole bilberries on VLDL levels. In fact this result goes against most other studies investigating the effects of bilberries on human health. This may suggest that these results are due to some confounding variable that has not been identified. The fact that the bilberries were effective at improving lipoproteins levels in the women at high risk of metabolic syndrome however does suggest that they may have a more positive effect in those with poorer metabolic profiles.
Dr Robert Barrington’s Nutritional Recommendation: Berries of all kinds have consistently been shown to be beneficial at protecting from disease. Incorporating a range of berries into the diet is a great way of conferring the variying benefits of different berry types.
RdB
