Excess fructose consumption has been hypothesized to be a cause of insulin resistance, obesity, elevated LDL cholesterol and triglycerides, leading to metabolic syndrome. In preliminary research, fructose consumption was correlated with obesity. A study in mice showed that a high fructose intake may increase adiposity.
One study concluded that fructose "produced significantly higher fasting plasma triacylglycerol values than did the glucose diet in men" and "...if plasma triacylglycerols are a risk factor for cardiovascular disease, then diets high in fructose may be undesirable".
Fructose is a reducing sugar, as are all monosaccharides. The spontaneous chemical reaction of simple sugar molecules binding to proteins is known as glycation. Showing potential cause of skin and bone damage in a rat model of diabetes, investigators suggested "that long-term fructose consumption negatively affects the aging process."
While a few other tissues (e.g., sperm cells and some intestinal cells) do use fructose directly, fructose is metabolized primarily in the liver.
Compared with consumption of high glucose beverages, drinking high fructose beverages with meals results in lower circulating insulin and leptin levels, and higher ghrelin levels after the meal. Since leptin and insulin decrease appetite and ghrelin increases appetite, some researchers suspect that eating large amounts of fructose increases the likelihood of weight gain.
Excessive fructose consumption may contribute to the development of non-alcoholic fatty liver disease.
A 2008 study found a substantial risk of incident gout associated with the consumption of fructose or fructose rich foods. Cases of gout have risen in recent years, despite commonly being thought of as a Victorian disease, and it is suspected that the fructose found in soft drinks (e.g., carbonated beverages) and other sweetened drinks is the reason for this.