I was interested recently to read the results of a study which assessed the antioxidant potential of several types of fruit juices and fruit drinks [1]. 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 red grape juice being hailed as the king of fruit juices. However, before we go scooting down to the supermarket for a dose of this latest super food, we might do well to consider red grape juice's prime constituent—sugar.
Like all fruit juices, red grape juice is crammed full of the stuff. One prominent brand contains 40 grams (g) of sugar per 240-milliliter (ml) serving. That works out at 16.66 g of sugar per 100 ml of drink. Coca-cola, on the other hand, contains 35 g of sugar per 330 ml, which works out at 10.6 g of sugar per 100 ml. What this means is that red grape juice contains more than 50 percent 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 red grape juice? That's a rhetorical question, obviously.
The sugar in fruit juices such as red grape juice comes, essentially, in the forms of glucose and fructose. As I have written before, 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. In the study, published in the journal Hepatology, rats were fed with a sugar solution containing either glucose or fructose [2]. Two notable effects of feeding fructose to rats were increased fat production in the liver and 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 polyphenol content and antioxidant activity simply does not give a full picture of their nutritional attributes and likely effect on health.
References:
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. Mar 16, 2007; [Epub. ahead of print]
Dr John Briffa is a London-based doctor, author, and health writer with an interest in nutrition and natural medicine.
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