I was interested recently to read the results of the study which assessed the ‘antioxidant’ potential of several types of fruit juices and fruit drinks . Of the 13 types of fruit juice tested, red grape juice came out on top with regard to antioxidant action, which appears to be related to its rich content of potentially disease-protective plant substances known as ‘polyphenols’. This study has led to purple grape juice being hailed as the king of fruit juices.
However, before we go scootling down to the supermarket for a dose of this latest superfood, we might do well to consider purple grape juice’s prime constituent ” sugar.
Like all fruit juices, purple grape juice is rammed full of the stuff. One prominent brand contains 40 g of sugar per 240 ml serving. That works out at 16.66 g of sugar per 100 mls of drink. Coca-cola, on the other hand, contains 35 g of sugar per 330 mls. Which works out at 10.6 g of sugar per 100 mls.
What this means is that purple grape juice contains more than 50 per cent MORE sugar than Coca Cola.
Could it be that this glut of sugar might offset some of the healthy properties ascribed to the polyphenols in purple grape juice? That’s a rhetorical question, obviously.
The sugar in fruit juices such as purple grape juice comes, essentially, in the forms of glucose and fructose. As I have written before on this site and elsewhere, while fructose is often seen as a ‘healthy’ form of sugar, the evidence suggests that it is anything but.
Just this week, for instance, a study was published which showed the considerable potential this form of sugar has to harm health. The study, published in the journal Hepatology, fed rats with a sugar solution containing either glucose or fructose .
Two notable effects of feeding fructose to rats were:
* Increased fat production in the liver
* Reduced effectiveness of the protein ‘leptin’ (among other things, leptin reduces fat production and enhances fat burning in the body)
In this study, some of the negative effects of fructose were found to be the result of impairment of the function of a receptor known as PPAR-alpha. This receptor is present in humans, and its activity in our species is lower than that in rats. This led one of the authors of the Hepatology study to speculate that the effect of fructose in humans should cause even worse effects than those revealed in rats.
There seems every reason to believe that the consumption of fructose might contribute to the rapidly rising rates of obesity seen around the World.
Take all of this together and there is good reason, I believe, for individuals to consume fruit juices with caution. Focusing on their polyphenols content and antioxidant activity simply does not give a full picture of their nutritional attributes and likely effect on health.
It should perhaps be borne in mind that the recent study highlighting purple grape juice’s wonderfood credentials was funded by an organisation known as the National Grape Co-operative, a consortium of US farmers operated by Welch’s who produce (you guessed it) purple grape juice.
Regular readers of this blog may remember that I recently reported on a study which found that studies funded entirely by the beverage industry are some 7½ times more likely to report favourable results than research which has received no industry funding .
1. Roglans N, et al. Impairment of hepatic Stat-3 activation and reduction of PPAR activity in fructose-fed rats. Hepatology 2007;45:778-788
2. Mullen W, et al. Evaluation of Phenolic Compounds in Commercial Fruit Juices and Fruit Drinks. J Agric Food Chem. 2007 Mar 16; [Epub ahead of print]