Blood lipids, glucose, and insulin
Other studies have looked at levels of blood lipids, glucose, and insulin in relation to fructose intake. In 2010 researchers at the University of California followed 23 overweight and obese adults, aged 43–70, for 10 weeks to measure the effects of drinking sugar-sweetened beverages. Participants were randomly assigned to consume 25% of their total calories from either glucose- or fructose-sweetened beverages (about 3 servings per day). At the end of the 10 weeks, participants who had drunk the fructose-sweetened beverages showed significantly higher levels of blood triglycerides and LDL cholesterol, as well as greater abdominal adipose (fat) tissue. They also had higher fasting blood glucose and insulin levels. In contrast, consuming the glucose-sweetened drinks had little or no effect on these measures.
Similar results were seen in a French study in which 16 healthy participants with a family history of Type 2 diabetes (but without diabetes themselves) consumed 35% of their calories from fructose-sweetened drinks for one week. At the end of the study, these participants showed an increase in abdominal fat, reduced insulin sensitivity, and higher levels of blood triglycerides — to a greater degree than did a control group of eight people with no family history of diabetes, who received the same treatment.
Nonalcoholic fatty liver disease
Another concern about fructose is its possible role in the development of nonalcoholic fatty liver disease (NAFLD), a liver disorder that is more common in people with Type 2 diabetes than in the general population. NAFLD is marked by a buildup of fat in the liver that causes inflammation and scarring, sometimes leading to liver failure. Fructose, research suggests, may contribute to the onset of NAFLD by way of its conversion to triglycerides in the liver.
In a study of 427 adults conducted at Duke University in 2010, consuming more than seven fructose-sweetened beverages per week was linked to a greater degree of a type of liver damage called fibrosis. In participants ages 48 and up, fructose intake was also associated with greater inflammation of the liver. The scientists conducting the study concluded that habitual consumption of fructose may lead to liver damage and set the stage for chronic liver disease.
Not all studies, however, paint as negative a picture of fructose and HFCS as the ones described above. Some researchers have found no connection between fructose intake and various health-related measures. Among participants in three large national studies of diet and disease risk, fructose from sweetened sodas, fruit juices, and fruit was not linked to high blood pressure, according to a 2008 analysis. In a separate study, Dutch researchers compared the effects of drinking four different beverages (milk, an artificially sweetened “diet” drink, and beverages sweetened with either high-fructose corn syrup or a glucose–sucrose blend) on hunger, as measured by how much of a yogurt–granola preparation participants ate afterward (40 healthy adults took part). Participants ate more after the diet drink, but there was no significant difference among the other beverages.
Finally, a study of 30 lean women conducted at the University of Rhode Island that measured blood glucose and insulin levels after consumption of beverages found no difference between those sweetened with HFCS and those sweetened with sucrose. There was also no difference in the resulting levels of the hormones ghrelin or leptin. This result does not directly contradict the University of Pennsylvania study, which found differences between beverages sweetened with pure glucose and pure fructose. However, it’s interesting to note that in this study, drinking a sucrose-sweetened beverage was associated with a higher desire to eat the next day, compared with drinking a HFCS-sweetened beverage.