A sweetener widely used in processed foods and soft drinks may contribute to weight gain in an unexpected way, according to new research. Scientists at the University of California, Irvine found evidence that high-fructose corn syrup (HFCS) can alter the gut in ways that increase the body's ability to absorb dietary fat, potentially promoting obesity and insulin resistance. High-fructose corn syrup is commonly found in sodas, fruit-flavored beverages, sweetened juices, breakfast cereals, baked goods, candies and other processed foods.
While excess sugar consumption has long been linked to obesity, researchers wanted to understand the biological mechanisms that connect fructose intake to weight gain. The team focused on what happens in the small intestine, where much of the body's dietary fructose is processed. Using mice, researchers examined the effects of blocking an enzyme called Ketohexokinase-C, which plays a key role in breaking down fructose in the gut.
For up to 12 weeks, the animals were given water containing high-fructose corn syrup. Researchers tracked body weight, fat mass, blood sugar levels and fat absorption. The results were striking.
Mice that lacked the fructose-processing enzyme in their intestines consumed the same number of calories as other mice but gained significantly less weight, remained leaner and showed better insulin sensitivity. According to the researchers, the difference appeared to stem from changes in the gut microbiome. When fructose was not broken down normally in the small intestine, it traveled farther through the digestive system, altering the composition of gut bacteria.
These microbial changes affected specialized structures called lacteals, tiny vessels in the intestine that absorb dietary fat. The altered mice developed shorter lacteals that absorbed less fat, meaning more fat passed through the body rather than entering the bloodstream. To test whether the microbiome was responsible, researchers transplanted gut bacteria from the modified mice into normal mice.
The recipients developed similar changes in their intestinal fat-absorbing structures and also absorbed less fat. The findings, published in Science Advances, suggest that fructose may influence body weight not only through the calories it provides but also by affecting how efficiently the body absorbs fat from food. However, the researchers caution that the study was conducted in mice, and the findings do not prove that high-fructose corn syrup has the same effect in people.
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