Fructose, the Evil Sugar

Photo by Moyan Brenn, Flickr

Photo by Moyan Brenn, Flickr

Not all sugar is created equal. The consumption of added sugars can have seriously adverse health effects, boosting insulin resistance, raising triglyceride counts and promoting weight gain, all of which increase risk factors for diabetes, hypertension and cardiovascular disease. According to a recent report from the Mayo Clinic the main culprit behind these adverse metabolic effects is a particular type of sugar — fructose. Though generally harmless in its natural form when found in whole foods like fruits and vegetables, fructose reaps havoc on the body when it is isolated, highly concentrated or added to processed foods and beverages.

Fructose is one of two sister molecules that make up sugar. The other is glucose which, according to the Mayo report, is less likely to cause adverse metabolic effects. This is because the body processes these two components quite differently. Glucose is more easily absorbed by our cells and organs to be used as energy. Fructose can only be processed in the liver, overloading that organ. While the body converts both glucose and fructose into fat cells, the fat produced from glucose is more easily burned into energy later. The liver needs three times the energy to burn fat made from fructose. Likewise, research has shown that isolated fructose decreases insulin sensitivity by 25% compared to isolated glucose. Insulin sensitivity means that the body requires more insulin in order to balance blood sugar, which is problematic and may lead to metabolic syndrome.

Isolated fructose also has been shown to promote a greater food intake, body weight, and liver weight in rodents. Again, this stems from the body’s difficulty absorbing fructose. Fructose causes the pancreas to release extra insulin, which in turn blocks the hormone leptin. When the leptin signal is blocked, the brain interprets this as starvation and, in short, tells the body to eat more, even though we don’t need more food.

The Mayo Clinic’s report was careful to distinguish between isolated or added fructose and fructose found naturally in whole foods. While the former is associated with kidney disease, diabetes, increased body weight, and overall metabolic syndrome, the latter is not. Indeed, whole fruits and vegetables may in fact protect against those very risks posed by isolated fructose. The report noted that the concentration of fructose found in whole foods is significantly less than in added fructose. Moreover, whole fruits and vegetables containing fructose are also accompanied by other ingredients, such as water, fiber, and antioxidants, which act to slow absorption and buffer the load of sugar. This is why fruit juice, which has a high concentration of fructose without the buffer of the whole fruit, shares the same markers of increased diabetes and weight gain as isolated fructose.

Making smart choices means that we must limit or altogether eliminate added sugars from our diet and, at the same time, increase whole fruits and vegetables.  Fructose is prevalent in every form of sweetener, both natural and manufactured.  Because approximately 75% of all packaged foods and beverages in the United States contain some form of sweetener, it has become exceedingly difficult for the American consumer to effectively manage their sugar intake.  This is why it is crucial that we make meals at home where it is possible to regulate the amount of added sugar to our food and limit the consumption of processed and packaged foods.