1 May 2014

Q&A with Jennie Brand-Miller

Prof Jennie Brand-Miller answers your questions. 

Are you better off drinking a small glass of fruit juice than a soft drink, cordial or sports drink?
Fruit juices have a low GI in most cases (40–50) and they contribute valuable micronutrients that you won’t find in alternative beverages. Some fruit juices are not low GI, e.g. Ocean Spray cranberry juice/drinks, which are around 60. Most soft drinks are in the GI range of 60–70. Sports drinks can be 70–80. A small glass of fruit juice is probably better than no fruit at all, but it always best to choose the whole fruit because it makes you feel fuller.

Does the high amount of fructose in juice have any effect on the release of glucose? 
No. When it comes to any sugary product (natural or otherwise), you have a mixture of sucrose, glucose and fructose. The ratio of fructose to glucose is about 1:1. Sucrose is digested quickly to glucose plus fructose before absorption. The fructose is metabolised in the liver and about 50% is converted to glucose and burnt as a source of fuel. While glucose is generally absorbed rapidly, it can be slowed by acidic solutions (e.g. all fruits are acidic) and very concentrated solutions. If fructose is consumed on its own, the process of absorption is slower and some may escape absorption. The presence of glucose increases the rate of absorption of fructose. The high proportion of fructose in fruit and fruit juice is one reason why they have a low GI. But it’s not the only reason. Very large amounts of fructose (70g a day or more) from any source can have adverse effects on the liver and blood lipids (fats) but few people consumed those quantities. The old adage applies: enjoy in moderation.