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Fructose Converts to Fat Faster Than Other Sugars

A general assumption is that fructose means fruit and most of us don’t worry about getting too much sugar from our fruits because we just don’t eat them very often.    We may be getting an overload of fructose without even being aware of it, though.  And what’s even worse is that a researcher from the UT Southwestern Medical Center in Dallas has just discovered that fructose in the diet converts to fat faster than any other sweeteners available today.

Dr. Elizabeth Parks, an associate professor of clinical nutrition, says the kinds of foods we eat, especially the carbohydrates, influence fat synthesis and may have as big an effect in a weight-loss diet as counting calories.  Traces of sugar occur naturally in many proteins (it’s the reason meats and pastries turn brown when cooked) but fruits and vegetables have the highest concentration of naturally occurring fructose.  To test her theory, Parks and her colleagues recruited six healthy people for a three-part study using glucose- and fructose-sweetened breakfast drinks.

Sucrose is the complex form of sugar, meaning it’s made from two simpler sugars - glucose and fructose.  The liver, working like a traffic cop, separates the glucose and fructose from the sucrose and sends each component, the glucose or the fructose, onto different routes, where one path leads to energy, to be burned as fuel as soon as possible, and the other path leads to long-term storage.  As fat.

When the traffic cops in the liver (the triglycerides) encounter fructose, they send it into storage to become fat more quickly than they route the glucose to fat storage.  Glucose is the preferred sugary fuel.  The higher the concentration of fructose in the diet, the more fructose available to be converted into stored fat.

Parks’ six study participants drank a specially prepared fruit drink for breakfast.  They ate a typical lunch four hours later.  Their glucose levels were monitored throughout and the rate of lipogenesis was watched.  Lipogenesis is the name of the process that converts the foods we eat into the fat we store, in all the places we’d rather not be storing it.

In blind and random order, each participant consumed a breakfast drink in one of three formulations.  One drink was 100% glucose, mimicking the formula used in glucose-tolerance tests instrumental in diagnosing diabetes.  A second drink was a 50:50 mixture of glucose to fructose.  The third was 75% fructose.

When comparing the 100% glucose breakfast to the 50:50 formula, lipogenic activity became quickly apparent and more vigorous after ingesting the fructose in the 50:50 formula.  The fat-building process was also activated when the 75% fructose mixture was consumed.

When the two high-fructose breakfast drinks were consumed, the build-up of stored fat continued into the afternoon, when the quick conversion of fructose to fat remained active  during digestion of the lunch meal.  The higher the concentration of fructose in the diet, the higher the rate of fat conversion.

All study participants were thin, in good health, with no known medical conditions that would impair sugar digestion and assimilation.  Researchers suggest the fat-building result of a high-fructose diet may be different, perhaps exaggerated, in people with impaired digestive functions, such as diabetics, the obese, and people suffering from food allergies.

A very large percentage of pre-sweetened beverages and mass-produced food products on the American food market are processed with a specially formulated 55%-fructose version of corn syrup.  It is listed in the ingredients list of most ready-to-eat food products and pre-sweetened beverages as “high fructose corn syrup” or simply HFCS.  The manufactured food industry embraces HFCS because it is easier to blend and sweeter than table sugar.  It’s also cheaper, too.  Ingredients are listed on food labels according to the proportional amount of an individual ingredient to the others, with the first item being the most abundant.  The closer to the beginning of the ingredients list, the more HFCS in the container.

Parks urges dieters to include a healthy amount of fruits in the daily diet while being mindful of fats, proteins, and all forms of added sugar.  She feels a diet high in HFCS thwarts most efforts to lose weight, since it converts to fat for storage quicker than other sugars.

The Parks study was funded by The Sugar Association, the Cargill Higher Education Fund, and the National Institutes of Health.  The Journal of Nutrition carries the full report in its current issue.

Source: UT Southwestern Medical Center

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