About half of our 350 daily added sugar calories come in the form of high fructose corn syrup (HFCS), which is the main sweetener in soft drinks and is added to packaged foods. Fructose, sometimes called fruit sugar, is a simple sugar that appears naturally in a variety of produce. Americans eat fructose mainly in the form of table sugar (which is half fructose and half glucose) and high fructose corn syrup (also part fructose and glucose). We all know that overeating sweets can make us gain weight. In his book, The Sugar Fix, Richard J. Johnson, MD, professor of medicine and chief of the Division of Renal Diseases and Hypertension at the University of Colorado in Denver, goes a little further. He puts forth the controversial theory that fructose, whether in table sugar or HFCS, poses risks to our well-being. MORE asked him to explain:
Q: What got you interested in fructose?
A: I’m a specialist in high blood pressure. Part of my work involves trying to figure out what gives rise to primary hypertension, which is the hypertension that’s not caused by another medical condition. In my research, we discovered that, in laboratory animals, if you raise levels of uric acid—a waste product that’s excreted through the kidneys—then their kidneys hold onto salt and this leads to high blood pressure. Elevated uric acid levels are common in subjects with obesity and high blood pressure, and in one study we found that nearly 90 percent of adolescents with newly diagnosed high blood pressure had high uric acid in their blood. Furthermore, I worked with Dr. Dan Feig at Baylor and showed in a pilot study that lowering uric acid with a drug could lower blood pressure in this group of patients.
So there’s a hypothesis, which needs to be confirmed by other research, that high uric acid levels put you at risk for high blood pressure and that lowering the uric acid levels might improve high blood pressure.
So the next question is, why are uric acid levels going up so much? Most uric acid in the body is a by-product from eating purines, which are largely found in meat and organ meats, whose consumption has been going down. What other food item raises uric acid? It’s fructose—and the consumption of that has grown dramatically.
Q. What other effects does fructose have on the body?
Fructose changes you. It appears to cause resistance to the appetite-suppressing hormone leptin, and there’s some evidence that it depletes your energy, i.e. the amount of spontaneous exercise you engage in. Maybe all those Americans are sitting in front of TV sets instead of moving around because their energy has been depleted by eating too much fructose. There is research being conducted at the University of California, Davis, in which people have been put on diets where 25 percent of their calories are coming from either fructose-sweetened drinks or ones sweetened by glucose. After 10 weeks, both groups gained the same amount of weight, but the fructose group put on more pounds in the abdomen, which could lead to future heart trouble. The fructose group—but not the glucose group—also showed decreased insulin sensitivity, a potential precursor of diabetes.
Q Does this mean that eating fruit is dangerous?
A Natural whole fruits have a lot of things that counteract the bad effects of fructose like fiber, vitamin C, and resveratol, the antioxidant best known for being in red wine. Most natural fruits are not particularly problematic. The exceptions are apples, pears and watermelon, plus fruit juices which contain large doses of sugar.
Q How hard is it to stay on a low-fructose diet?
A In The Sugar Fix diet, we reduce sugar to one-third of what most people are eating. People who go on it will tell you that after a few weeks their urge for sugar falls dramatically. They feel better and have more energy. The hardest time is the first two weeks. There is no doubt that some people are addicted to sugar, and it is difficult for them to get off it—it requires a bit of determination. One trick is to eat sugar-free popsicles.