It is considered that overeating and lack of muscle tone is the main cause of a beer belly, rather than beer consumption. A 2004 study, however, found a link between binge drinking and a beer belly. But with most overconsumption, it is more a problem of improper exercise and overconsumption of carbohydrates than the product itself. Several diet books quote beer as having an undesirably high glycemic index of 110, the same as maltose; however, the maltose in beer undergoes metabolism by yeast during fermentation so that beer consists mostly of water, hop oils and only trace amounts of sugars, including maltose.