ietary fructose is increasingly being seen as the cause of obesity. This is because fructose is the primary driver of mammalian insulin resistance that leads to abdominal fat accumulation and development of the metabolic syndrome. The most common fructose containing molecule in the human diet is sucrose, but artificial high fructose corn syrup is increasingly adulterating the food supply, particularly in the United States of America. Many argue that sucrose and fructose are present naturally in fruit and as such cannot be dangerous in moderation. However, in nature sucrose and fructose are accompanied by high amounts of dietary fibre and other constituents that modify the digestion rate of the sugars and change their physiological effects. Soft drinks, cakes and other processes foods are devoid of nearly all fibre, as this improves taste and increases shelf life. As a result the sucrose present causes significant detrimental changes to blood sugar.
That sucrose is not as metabolically damaging when fruit is present was demonstrated in research published recently in the American Journal of Clinical Nutrition1. Subjects comprised of twenty healthy women, and the study design was randomised, with a controlled cross-over design. Subject consumed whole blackberries or lingonberries as 150 g puree meals with 35 g of added sucrose, or berry fruit juice (equivalent to 150 g blackberries or lingonberries) with 35 g added sucrose. A test meal of just 35 g sucrose with no berries was used as a control. When the researchers measured the response to the meals they found that the presence of berries reduced the rate of insulin release and caused a lower postprandial insulin concentration in the blood. This they showed was due to a slower rate of glucose absorption. The whole berries had a more pronounced effect than the fruit juice, but both were significantly different to the control.
The authors also noted that the berries cause a lower hypoglycaemic response and a lower fatty acid release post postprandially, suggesting that blood sugar control had been improved. Therefore the presence of factors within fruit may prevent the detrimental effects of sucrose on human metabolism. This effect is thought to be due mainly to fibre, but the ability of juice to have a smaller effect may suggest that other components within the fruit are able to influence the rate of sucrose digestion and glucose absorption. This may be the presence of other natural sugars within the fruit that inhibit certain enzymes such as sucrase, and transporters required for the uptake of fructose and glucose. In a previous study, the same authors also showed that a combination of different berries including bilberries, blackcurrants, cranberries and strawberries were able to significantly decrease postprandial glycaemia.
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