During the past decade, fructose-containing sweeteners have been linked to numerous health problems, including obesity, hypertension, elevated blood triglycerides and LDL (low-density lipoprotein, or “bad”) cholesterol, and insulin resistance — suggesting that fructose may play a role in the development of atherosclerosis, metabolic syndrome, and diabetes. Another possible negative effect of high fructose consumption is its potential role in the onset of nonalcoholic fatty liver disease. The following sections describe some of the findings of studies that looked at the role of fructose in various health conditions.
One of the most hotly contested topics related to fructose is its potential role in the development of obesity. Consuming a large amount of fructose is known to raise the level of triglycerides in the blood; elevated triglycerides are often seen in obese individuals. Some researchers believe that high levels of dietary fructose contribute to weight gain by stimulating the deposit of triglycerides in fat tissue throughout the body.
The fructose–triglyceride connection was explored in a small clinical study conducted at the University of Texas, published in 2008, in which six healthy volunteers were fed one of three different breakfast drinks daily, with the drink chosen at random. The three drinks were sweetened, respectively, with 100% glucose, 50% each glucose and fructose, and 25% glucose and 75% fructose. Levels of blood triglycerides were found to be 200% higher following ingestion of a beverage containing fructose, compared with the glucose- only beverage.
Other studies have yielded similar results, including one conducted at the University of Pennsylvania that enrolled 12 normal-weight women. Significantly higher levels of triglycerides were seen after just one day among those randomly chosen to drink 25% of their daily calories from a fructose-sweetened beverage, compared with the remaining women, who drank a glucose-sweetened beverage. Women who drank the fructose-sweetened beverage also displayed significantly lower levels of leptin and higher levels of ghrelin — two hormones associated positively and negatively, respectively, with appetite control. An imbalance of these hormones is believed to play a role in obesity in many individuals.
In a study conducted at the University of Toronto, scientists looked at how drinking beverages with different ratios of glucose to fructose affected participants’ intake of food later on; a total of 31 men took part. The researchers found that the men’s food intake was lower after they drank high-glucose rather than high-fructose beverages. Drinking high-fructose beverages also led to higher blood levels of potentially harmful uric acid.
Two recently published studies show that a moderate to high intake of fructose may be linked to an increased risk of hypertension — possibly by causing the kidneys to absorb extra water and sodium. Dietary and health information collected from 4,528 healthy adults through the National Health and Nutrition Examination Survey (NHANES 2003–2006) showed that consumption of more than the average of 74 grams per day of fructose (equivalent to about 2 1/2 servings of soft drinks) led to a 77% higher risk of blood pressure elevated to 160/100 mm Hg or higher, compared with a normal reading of 120/80 mm Hg.
And in a small clinical trial conducted at the Mateu Orfila Hospital in Spain, researchers fed 74 healthy men 200 grams of supplemental fructose a day (about 3–4 times the amount most people get in their diets) for two weeks. In addition, half of the men received allopurinol, a medicine used to lower blood levels of uric acid and relieve the painful symptoms of gout. At the end of the study, both blood pressure and uric acid levels were significantly higher in men who did not receive the allopurinol.