New research from UT Southwestern Medical Center shows the amazing speed that our bodies make body fat from fructose. One of the reasons why low carb diets help you lose weight is that they reduce your intake of fructose.
Even though fructose, a type of sugar, is found naturally abundance in fruit, it is also added to many processed foods. Fructose is probably best known for its presence in the sweetener called high-fructose corn syrup (HFCS), which is typically 55 percent fructose and 45 percent glucose.
It unfortunately has become the preferred sweetener for many food manufacturers. This is because it is cheaper, sweeter and easier to blend into beverages than table sugar.
Sugar Type As Important as Calories
Dr. Elizabeth Parks, lead author of the study , said her team’s findings infer that the right kind of carbohydrates you eat may be just as important in weight control as the number of calories you eat. The study appears in the Journal of Nutrition.
“The message from this study is powerful because body fat synthesis was measured immediately after the sweet drinks were consumed,” Dr. Parks said. “The carbohydrates came into the body as sugars, the liver took the molecules apart like tinker toys, and put them back together to build fats. All this happened within four hours after the fructose drink. As a result, when the next meal was eaten, the lunch fat was more likely to be stored than burned.
“This is an underestimate of the effect of fructose because these individuals consumed the drinks while fasting and because the subjects were healthy, lean and could presumably process the fructose pretty quickly. Fat synthesis from sugars may be worse in people who are overweight or obese because this process may be already revved up.”
Blame Obesity Epidemic on Fructose?
Dr. Parks said that people trying to lose weight shouldn’t totally eliminate fruit from their diets but that limiting processed foods containing the sugar may help.
“There are lots of people out there who want to demonize fructose as the cause of the obesity epidemic,” she said. “I think it may be a contributor, but it’s not the only problem. Americans are eating too many calories for their activity level. We’re overeating fat, we’re overeating protein; and we’re overeating all sugars.”
In the research, six healthy individuals went through three tests where they had to drink a fruit drink mix. In one test, the breakfast drink was 100 percent glucose, similar to the liquid doctors give patients to test for diabetes — the oral glucose tolerance test.
In the second test, they drank half glucose and half fructose, and in the third, they drank 25 percent glucose and 75 percent fructose. The tests were random and blinded, and the subjects ate a regular lunch about four hours later.
The researchers found that lipogenesis, the process by which sugars are turned into body fat, increased significantly when as little as half the glucose was replaced with fructose. Fructose given at breakfast also changed the way the body handled the food eaten at lunch.
After fructose consumption, the liver increased the storage of lunch fats that might have been used for other purposes.
Elizabeth J. Parks, Lauren E. Skokan, Maureen T. Timlin, and Carlus S. Dingfelder
Dietary Sugars Stimulate Fatty Acid Synthesis in Adults
J. Nutr. June 2008 138: 1039-1046
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