How Fructose In the Diet Contributes To Obesity

An anonymous reader quotes a report from ScienceDaily: Eating fructose appears to alter cells in the digestive tract in a way that enables it to take in more nutrients, according to a preclinical study from investigators at Weill Cornell Medicine and NewYork-Presbyterian. These changes could help to explain the well-known link between rising fructose consumption around the world and increased rates of obesity and certain cancers. The research, published August 18 in Nature, focused on the effect of a high-fructose diet on villi, the thin, hairlike structures that line the inside of the small intestine. Villi expand the surface area of the gut and help the body to absorb nutrients, including dietary fats, from food as it passes through the digestive tract. The study found that mice that were fed diets that included fructose had villi that were 25 percent to 40 percent longer than those of mice that were not fed fructose. Additionally, the increase in villus length was associated with increased nutrient absorption, weight gain and fat accumulation in the animals. After observing that the villi were longer, the team wanted to determine whether those villi were functioning differently. So they put mice into three groups: a normal low-fat diet, a high-fat diet, and a high-fat diet with added fructose. Not only did the mice in the third group develop longer villi, but they became more obese than the mice receiving the high-fat diet without fructose. The researchers took a closer look at the changes in metabolism and found that a specific metabolite of fructose, called fructose-1-phosphate, was accumulating at high levels. This metabolite interacted with a glucose-metabolizing enzyme called pyruvate kinase, to alter cell metabolism and promote villus survival and elongation. When pyruvate kinase or the enzyme that makes fructose-1-phospate were removed, fructose had no effect on villus length. Previous animal studies have suggested that this metabolite of fructose also aids in tumor growth. From an evolutionary standpoint, the findings make sense. "In mammals, especially hibernating mammals in temperate climates, you have fructose being very available in the fall months when the fruit is ripe," said one of the researchers. "Eating a lot of fructose may help these animals to absorb and convert more nutrients to fat, which they need to get through the winter." Humans, on the other hand, did not evolve to eat the amount of fructose they consume now.

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