The fructose story
Fueling the sugar debate is consumers’ confusion over the effects of HFCS, which has received the lion’s share of public scrutiny on the sugar front, even to the point where consumers often consider cane sugar to be healthful in comparison. However, most nutrition experts consider all added sugars, such as HFCS, table sugar and honey, to be similar in their effects.
The problem with HFCS is that it’s so pervasive in our food system. The intake of HFCS increased by more than 1,000 percent between 1970 and 1990, far exceeding the changes in intake of any other food or food group in American diets. HFCS now represents more than 40 percent of the caloric sweeteners added to foods and beverages and is the sole caloric sweetener in soft drinks.(7)
Many consumers mistakenly believe that HFCS, a corn-derived sweetener commonly used in food and beverage processing, is pure fructose, when in fact it’s 42 to 53 percent glucose and 42 to 55 percent fructose, depending on the type, making it similar in composition to table sugar, which is one-half glucose and one-half fructose. HFCS is produced from corn syrup, nearly all glucose, which undergoes enzymatic processing to increase the fructose content and is then mixed with glucose.(2)
According to AHA, studies suggest that excessive fructose consumption may play a role in insulin resistance, obesity, hypertension, dyslipidemia, and type 2 diabetes in humans.(2) In a University of California, Davis review on fructose and metabolism, researchers reported that the hepatic metabolism of fructose favors lipogenesis, which may contribute to hyperlipidemia and obesity.(8)
“Fructose clearly is metabolized differently from glucose,” Klurfeld explains. “Fructose is metabolized primarily in the liver, and there are both advantages and disadvantages to that. The advantage is that eating fructose doesn’t raise blood glucose or insulin levels, both of which, when elevated above the normal range, are thought to contribute to a variety of diseases ranging from heart disease to obesity to several forms of cancer or even the normal aging process. The disadvantage is that when fructose is metabolized in the liver, it’s used preferentially to make fats. However, since fructose is almost never eaten by itself and is usually in approximately equal amounts with glucose, neither of the above conditions predominates.”
What about the impact of sugar on glycemic response and insulin secretion? It’s not unusual for nutrition professionals to counsel patients to avoid added sugars because of their effects on blood glucose. Increasingly, health professionals are recognizing the usefulness of the glycemic index (GI) to educate clients on the quality of carbohydrates and their impact on glycemic response. The American Diabetes Association (ADA) reports that the type of carbohydrate does have an effect on blood glucose, thus the GI may be helpful in fine-tuning blood glucose management.(9)
Indeed, some studies have found that low-GI diets can reduce the risk of heart disease, inflammatory diseases,(10,11) and type 2 diabetes.(12) Consuming low-GI carbs also may delay hunger and reduce subsequent energy intake compared with higher-GI carbs.(13) And some research has found that weight-loss benefits from low-GI diets.(14) However, not all studies have found such promising results, and investigators stress that more research is needed.
Does a low-GI diet protect against insulin resistance? After all, insulin resistance is associated with several health problems, such as type 2 diabetes, obesity, high blood pressure, heart disease, and stroke. The Insulin Resistance Atherosclerosis Study (IRAS) showed a lack of association between GI, glycemic load, and carbohydrate intake and measures of insulin sensitivity, insulin secretion, and adiposity.(15) The strongest link to insulin resistance remains excess weight and lack of physical activity.(16)
It’s important to consider that the effects of a food’s GI may be muddled with other factors. The benefits seen with low-GI diets may be related to fiber and other components found naturally in whole grains, fruits and vegetables.(17) In addition to sugar, many carbohydrate-containing foods such as refined grains, cereals and breads rank high on the GI. The view that sucrose consumption results in higher blood glucose levels than starch is a common misperception. Indeed, cooked starch, such as bread, rice and potatoes, evokes glucose responses similar to glucose.(2)
“The glycemic response is the greatest for glucose, not fructose,” Slavin says. “So sugar causes less glycemic response than glucose or starch. Therefore HFCS, which is usually 55 percent fructose, has the lowest glycemic response compared to sucrose with 50 percent fructose or starch with 100 percent glucose.”
At the Annual Nutrition & Health Conference Lustig said, “Fructose induces insulin resistance.” But Klurfeld says that while it was once thought that high sugar intake promotes insulin resistance, this was disproven. “If someone consumed nothing but glucose in large amounts, this might occur, but since we consume a mixture of sugars, it doesn’t happen. In fact, fructose doesn’t require insulin for its metabolism,” Klurfeld says.
According to a review published by a researcher at the Diabetes and Vascular Research Centre in the United Kingdom, animal studies have consistently shown the effect of high-sucrose and high-fructose diets in decreasing insulin sensitivity, but studies in humans have produced conflicting results, with limited evidence demonstrating a negative effect on insulin sensitivity at higher intakes of fructose or sucrose (generally greater than 30 percent of daily calories from sucrose and greater than 15 percent of daily energy from fructose). However, observational studies in humans haven’t shown a link between sucrose consumption and insulin sensitivity. The differences in the pattern of postprandial responses between fructose and sucrose may offer a possible explanation for the conflicting results on insulin sensitivity.(18)
The IRAS study also found no association between sucrose intake and insulin sensitivity.(19) But a study of 16 overweight Latina adolescent females who completed a 12-week modified carbohydrate intervention found that greater reductions in added sugar intake showed significantly greater improvements in insulin secretion following a modified carbohydrate nutrition intervention.(20) And sugar-sweetened beverage intake was linked with hepatic insulin resistance in the Framingham Offspring Study.(21)
The sugary beverage conundrum
While researchers may be cautious about the evidence linking sugar to obesity and other health concerns, they seem more clear on the relationship between sugar-sweetened beverages and health. “Sugar in beverages is a problem for several reasons,” Brownell says. “One, [sugar-sweetened beverages] are the greatest source of added sugars in the diet. Two, they’re completely empty calories. Three, they’re very heavily promoted. Four, the body doesn’t seem to recognize calories very well when they’re delivered in liquids; you don’t feel as full. Five, it’s possible that sugar triggers an addictive process in the brain.”
Between 1970 and 2000, per person daily consumption of caloric soft drinks increased by 70 percent from 7.8 to 13.2 oz.(2) Carbonated sodas provided 22 percent of the reﬁned and added sugars in the 2000 American food supply compared with 16 percent in 1970.(1,2)
Several studies have linked sugar-sweetened beverage intake with higher energy intake, greater body weight, health problems, and poor nutrition.(2) People don’t compensate as well for calories in beverages, compared to calories in solid food, which may impact weight control.(22) A California study found that adults who drink one or more sodas every day are 27 percent more likely to be overweight or obese than those who don’t drink soda.(23) And women who regularly consume sugar-sweetened beverages were shown to have a higher risk of coronary heart disease.(24)
Best expert advice
It seems there are more questions than answers when it comes to the role of sugar for human health. “The science of food and health is young,” Gazzaniga-Moloo says, “Our bodies are complicated machines, and the fuel we feed it and how it’s metabolized by the body is unique to each individual. It’s complicated science with few definitive, concrete answers at this point.”
The AHA guidelines on sugar call for a prudent upper limit intake of one-half of the discretionary calorie allowance, which for most American women is no more than 100 kcal/day, and for most American men no more than 150 kcal/day from added sugars.(2) Both Brownell and Gazzaniga-Moloo recommend using these guidelines for educating the public.
Foods and beverages that are high in added sugars and low in nutrients can displace nutrient-rich foods in the diet so that it becomes difficult for people to meet the recommended intake for macronutrients and micronutrients. In fact, the Dietary Guidelines state that a diet with no more than 5 to 15 percent of calories from solid fats and added sugars can meet the USDA food pattern designed to meet nutritional needs within calorie limits. Thus, they advise limiting the amount of added sugars when cooking or eating, and consuming fewer and smaller portions of foods and beverages that contain them.(6)
“The best – and most boring – advice is variety and moderation in sugar intake and everything else,” Klurfeld says. “The key to defining how much sugar to consume is to balance calories in with calories expended. Since most Americans do very little physically, the only options are to eat less or move more, and more activity increases and helps maintain muscle mass, which is associated with better health.”