December 2008

The fructose boom
To most people “sugar” means table sugar, which is sucrose and is made from sugar cane or sugar beets. There are, however, many different types of sugar: in their pure form they have names such as glucose, fructose, and lactose (milk sugar), as well as sucrose (which is actually half fructose, half glucose). Instead of these chemical names, most of us identify sugars by their sources, such as maple syrup, honey, corn syrup, and molasses. As far as basic nutrients go, sugar is sugar. But some recent research suggests that fructose, at least in the large quantities many Americans are now eating, poses special health problems.

Where are we getting all this fructose? It is the primary sugar in fruit and honey, but those are not the sources of most of our fructose. We’re consuming millions of tons of high-fructose corn syrup (HFCS), which now supplies about 10% of all calories in the U.S. diet. The figure is closer to 20% for some people, including many children. In addition, sucrose supplies lots of fructose. Many foods and beverages are also sweetened with fruit juice concentrate, which sounds healthy but is simply sugar, with an even higher proportion of fructose.

HFCS, developed in the 1960s, is a liquid sweetener made from corn starch. Corn contains little fructose, but manufacturers use a special process to boost the fructose content (usually to 55%) and thus make it sweeter. In the U.S. about two-thirds of HFCS is used in soft drinks; the sweetener is also added to everything from baked goods and candies to breakfast cereals and pasta sauces. HFCS is so widely used because it is sweeter than sucrose, easy to blend with other ingredients, and cheap. Corn as a crop is subsidized by the government, and until recently we grew more of it than we could use.

Forty years ago we consumed almost no HFCS and thus much less fructose, but now it has pushed sucrose aside as the leading additive in our food supply. Humans have never consumed anything close to this much fructose before, and there’s some evidence that our bodies can’t handle large amounts well.

A long list of worries, but few certainties
The body digests, absorbs, and utilizes fructose differently than glucose, our main source of energy. For one thing, fructose doesn’t stimulate insulin secretion. This can be good: small to moderate amounts of fructose can help people with Type 2 diabetes keep their blood sugar under control. But studies, mostly in animals, have found that large amounts of fructose may actually increase the risk of diabetes, possibly by promoting insulin resistance.

In addition, unlike glucose, fructose is mostly broken down in the liver, where it can affect the production of various lipids (fats and related substances). Human as well as animal studies suggest that high levels of fructose can contribute to cardiovascular disease by boosting triglycerides (fats in the blood), lowering HDL (“good”) cholesterol, and increasing levels of smaller, more harmful LDL (“bad”) cholesterol particles. Though the evidence is not consistent, high fructose intake has been linked to kidney and liver disease, high blood pressure, systemic inflammation, and increased formation of cell-damaging free radicals. As with so many things, genetic factors may play a role in how the body copes with large amounts of fructose.

Fructose and weight
Is there something unique about fructose that can cause extra weight gain? Some researchers point to the increased consumption of HFCS as a prime culprit in the rising obesity rate. They claim that because fructose doesn’t stimulate insulin and may affect other hormones related to appetite, it does not reduce hunger much and thus can encourage overeating. But some recent studies found no difference in the effect on these hormones, hunger, satiety (the feeling of fullness), or subsequent calorie consumption, compared to other caloric sweeteners. Nonetheless, fructose and HFCS clearly play a role in obesity, but it may be just a matter of extra calories.

Fruit yes, soda no
Do not cut back on fruit because it contains fructose. Americans get only a small portion of their fructose from fruit. You would have to eat several servings of fruit at one sitting to get as much fructose as in a can of soda. (A cup of some fruit juices, however, can naturally contain nearly as much fructose as a can of soda, so you should probably limit yourself to one cup a day.) In any case, fruit is great food, containing fiber, vitamins, minerals, and phytochemicals; it is filling and relatively low in calories. Fruit consumption goes hand in hand with many health benefits.

In contrast, HFCS, like sucrose, simply adds calories to highly processed foods lacking in nutrients. In moderation HFCS or fruit juice concentrate won’t hurt you. The biggest problem is the sheer quantity of HFCS we’re consuming and the hundreds of calories it adds to the average American’s diet every day. According to Dr. Ronald Krauss, a member of our Editorial Board who has done research on fructose and its effect on blood chemistry, “nearly everyone in the field agrees that excess consumption of sugar, and HFCS in particular, contributes to obesity, and I think there will soon be a campaign to reduce it in our food supply, as there was with trans fat.”

Words to the wise: If you consume lots of HFCS-sweetened soft drinks and foods, or lots of any type of added sugar, cut down. Even though the jury is still out as to whether HFCS is significantly worse than sucrose, if you cut down on foods and drinks that contain it, you’ll almost inevitably improve your diet.

UC Berkeley Wellness Letter, August 2008