Fructose promotes hormonal imbalance and weight gain

Fructose is the sugar in fruit, vegetables, grains and honey. It is also used as a popular sweetener in prepared foods including and perhaps especially in soft drinks in the form of high fructose corn syrup (HFCS). According to a 2004 article in the American Journal of Clinical Nutrition, HFCS makes up over 40 percent of caloric sweeteners added to our food; possibly because it is inexpensive and appeals to consumers who love the taste. Dramatic increases in obesity correspond closely to the introduction and growing use of HFCS suggesting it has played a role in this epidemic. Although a recent study questions the special role of fructose in obesity, other studies find that it promotes fat storage and hormonal imbalances associates with weight gain.

Does fructose promote weight gain?

While much research has linked fructose consumption with weight gain, a recent study reported in Reuters seems to suggest otherwise. The scientists evaluated a variety of different studies all of which compared two groups of people who ate the same number of calories. However, one group got on average 17 percent of their calories from fructose. Overall, results showed little difference in weight gain between the two groups and the researchers concluded that fructose in and of itself does not promote weight gain more than other carbohydrates.

Other studies found very different results.

Fructose, sucrose and the brain

In 2011, scientists at the Oregon Health & Science University used functional MRI images to evaluate reactions to both fructose and sucrose in the brains of nine normal weight subjects. In the part of the brain that controls responses to food they found a reaction to glucose that was opposite that of the reaction to fructose. The scientists stated that these results support previous research on animals and link fructose to obesity.

Fructose stored as fat

When we eat glucose, our bodies convert some of it to fat and burn the rest. On the other hand, studies show that much of fructose is stored as fat. In 2008, an article in the Journal of Nutrition reported on a study in which scientists looked at this particular question. Six study subjects did three different tests in which they had a breakfast drink that was either 100 percent, 50 percent or 25 percent glucose with the balance being fructose. Results showed a significant increase in the conversion of sugar into fat (lipogenesis) after just half of the sucrose was replaced by fructose. Subjects who drank more fructose also stored more fat after eating lunch about four hours later.

Fructose impacts fat regulating hormones

A number of hormones impact the body’s energy use and consumption. Amongst these are insulin which helps cells obtain the nutrition they need from blood sugar, leptin which signals the brain when we are full and can stop eating, and ghrelin which stimulates appetite. We are all healthier and thinner when these hormones have a good, working relationship than when they do not. Fructose can change this relationship.

A 2004 study in the Journal of Clinical Endocrinology and Metabolism took blood samples from two groups of women after they ate meals accompanied by either a glucose or a fructose sweetened beverage. Their results showed that the fructose drink was associated with a reduction in leptin as well as postprandial increases in the appetite stimulating hormone, ghrelin.

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Author: Celeste M. Smucker, MPH, PhD

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