In the small, short-term study, 48 adult participants between the ages of 18 and 40 limited their daily consumption of sugary beverages for five weeks. They were then divided into three groups, with each group consuming 25 percent of their daily calories as beverages containing sugar in the form of fructose, high-fructose corn syrup, or glucose, respectively. (Federal dietary guidelines suggest that Americans consume no more than 25 percent of their daily calories as added sugar.) Within two weeks, those consuming fructose or high-fructose corn syrup had increased blood concentrations of three known risk factors for cardiovascular disease: LDL cholesterol, triglycerides, and a protein known as apolipoprotein-B, which can cause plaque buildup in arteries.
We spoke with Kimber Stanhope, PhD, the study’s senior author, and a research scientist in the department of molecular biosciences, School of Veterinary Medicine, at UC–Davis. She told us that she was surprised by the study’s results: She expected that the glucose in high-fructose corn syrup (high-fructose corn syrup is roughly half fructose, half glucose) would mitigate the effects of the fructose. Says Stanhope, “In 2009, we published results from a study which showed that consuming 25 percent of daily calories as fructose increased circulating lipids and lipoproteins in older, overweight, and obese adults, while consumption of glucose did not." So she expected that the effects of the half-glucose HFCS would be less than those of pure fructose. "But the changes in the lipoproteins were as high in subjects consuming HFCS as those consuming the purely fructose-sweetened beverages.” She says that more studies are needed to confirm this unexpected pattern, and to determine if it is a result of an effect of consuming fructose and glucose in combination.
So what exactly are the differences between all these different types of sugar? We asked Stanhope to break it down for us non-scientists. Here’s her primer on understanding sugar:
Fructose is naturally occurring in fruit (at levels of 1 to 8 percent) and honey (about 38 percent). Pure fructose is rarely used as an added sweetener.
Glucose is naturally occurring in fruit (1 to 7 percent) and honey (about 31 percent). Pure glucose is not commonly used as a sweetener, except for corn syrup (such as Karo’s), which is a glucose syrup made from cornstarch. Other commonly eaten foods that contain glucose (in the form of complex carbohydrates) are grains (for example, wheat, oats, barley, rye) and veggies (potatoes, squash, and beans). Complex carbohydrates consist of chains of glucose molecules, which are broken down to single glucose molecules during digestion.
Sucrose is made up of a glucose molecule attached to a fructose molecule; it’s naturally occurring in fruit (0.1 to 6 percent), sugar beets (17 percent), and sugar cane (10 percent).
High-fructose corn syrup (HFCS) is not naturally occurring. The glucose syrup made from cornstarch can be turned into a fructose syrup by adding an enzyme that changes the glucose molecules into fructose molecules. By mixing that fructose syrup with glucose syrup, different formulations of HFCS can be made. For her study, Stanhope and her colleagues used HFCS-55, which is 55 percent fructose and 45 percent glucose.
The takeaway for heart health? Watch levels of sucrose and high-fructose corn syrup, which are the sugars that are most commonly used to sweeten foods and beverages, says Stanhope. When it comes to the American diet, Stanhope expects that the effects of sucrose consumption, though not looked at in this study, would be comparable to those of HFCS, since its composition (50 percent glucose/50 percent fructose) is very similar to the composition of the HFCS used for this study (45 percent glucose/55 percent fructose).
Not all fructose-containing beverages are the same, says Stanhope. Orange juice, for example, has about the same amount of fructose as soda, but it also contains many micronutrients, such as vitamin C. And there's not much data comparing the effects of fruit juices and HFCS-sweetened soda on cardiovascular disease risk, she notes. "I think it would be interesting and important to conduct these studies.”
On the other hand, agave nectar, which contains mostly fructose, is touted for its low glycemic index. But Stanhope says that another recently published study suggests that it is in fact the fructose, not the glucose and related insulin spikes (glycemic index), that contributes to the adverse effects of the consumption of sugar-sweetened beverages on lipid levels and insulin sensitivity.
While scientists sort out the varying effects of different forms of sugar, you can take steps to keep your overall sugar intake at a low and healthy level. Here's how:
• Cut down on added table sugar (sucrose). This is a relatively easy step, just watch for opportunities to cut back in a typical day. Maybe one spoonful of sugar in your coffee instead of two, or a sprinkle on top of your grapefruit instead of a whole spoonful. If you bake, check out our healthy recipe finder for recipes that aren't overloaded with sugar.
• Pass on packaged snacks whenever possible. What’s trickier—but vital—is avoiding the sugar, typically HFCS, found in sodas and other beverages, and in products as wide ranging as ice cream, cookies, cereal, chips, bread, ketchup, barbecue sauce, jam, canned fruit, yogurt, and frozen dinners. The fact is, food makers routinely cram extra fat and sugar into their wares, knowing that it will make us overeat and buy more of their products. Choosing whole fruits and vegetables whenever you can is one defense. When you do go for a packaged snack (we all do, sooner or later), be label-aware and go the extra mile in seeking out less sugary brands.
• Break the sugar addiction. Addiction to sugar is no joke: Sugar stimulates some of the same neurotransmitters as, and in a manner similar to, alcohol, cocaine, and other drugs of abuse. Rodale.com advisor Jeffrey Rossman, PhD, offers 10 Tactics for Overcoming Sugar Addiction.