It has been estimated that 11 percent of all cases of heart failure in men and up to 14 percent in women are due to obesity. Since the physiological links between these conditions are still not fully understood, the impact obesity has on heart disease is difficult to predict, and it can be therefore harder for doctors to identify people at risk for heart disease. Researchers and doctors are still exploring dietary factors that contribute to obesity and the development of heart disease and diabetes. Do nutrients like fructose interfere with benefits of weight-loss?
Questions such as these have led Dr. Joshua Wooten, assistant professor of exercise in the SIUE School of Education, Health and Human Behavior, to study how these three major health concerns might be linked.
One of his focus areas is high-fructose consumption. It is now estimated that about 60 percent of the average American diet consists of fat, although, according to 2005 U.S. Government dietary guidelines, adults should only get about 20-35 percent of their daily calories from fat. Yet, a more surprising issue is the rising level of fructose consumption, which now stands at 20 percent of the average American diet.
Fructose, used as a sweetener, is one of the most common ingredients in packaged foods nationwide and has recently become a major concern for public health advocates. It is found in food commonly deemed unhealthy, but it also occurs naturally in fruits and vegetables. Soft drinks are among the more obvious culprits, since they contain large amounts of high-fructose corn syrup. As these easily-accessed items have become increasingly more common in the U.S. diet, fructose intake has risen dramatically.
The potential dangers in high-fructose consumption, according to Wooten, include not only obesity but also liver and heart disease. “We’re interested in examining how the liver deals with high-fructose consumption and how it may impede weight loss-related health benefits,” he said. He hypothesizes that the combination of a high-fat and high-fructose diet leads the liver and heart to store more fat, increasing the risk for both type 2 diabetes and heart failure. Wooten also believes that when a person sustains high level of fructose consumption, the rate of weight loss will decrease, even if one lowers his or her fat intake.
In one experiment, Wooten explored the impact of high-fructose consumption during weight-loss in order to understand how fructose affects fat and carbohydrate metabolism in the heart and liver. While it is often assumed that a lower fat diet will result in a higher rate of weight loss, high-fructose consumption may hamper this process. Wooten and his team gave two groups of obese mice each a low-fat diet, while measuring and their rate of weight loss over six weeks. The difference in the groups’ diets, however, came from the amount of fructose dispensed: one group received a 20 percent fructose drinking solution to match the national human average, while the other was given regular drinking water.
According to Wooten, initial results revealed that “continued high-fructose consumption during weight loss resulted in 42 percent higher circulating triglyceride levels when compared to mice consuming regular drinking water.” Essentially, significantly more fat was circulating in the body and more stored fat was found in the livers of high-fructose mice over their water-drinking counterparts.
“When too much fructose is ingested over several weeks, the liver becomes overwhelmed and begins to become insulin resistant,” Wooten said. “The primary job of insulin is to stimulate the uptake of circulating glucose (sugar) into cells. Insulin also regulates release of lipids or triglycerides (fat) into the blood stream. When the liver becomes insulin resistant, the release of triglycerides into the blood stream increases. Furthermore, the excess fructose is converted into triglycerides and stored in the liver, leading to lipotoxicity, also known as fattening of the liver.” In addition to these negative effects on the liver, Wooten is exploring further to determine if a high-fructose diet also affects the heart’s fat and carbohydrate metabolism.
While it may seem that low-fat and high-fructose diets are an uncommon combination, this does not appear to be the case. In many low-fat diets, fructose levels can elevate when one takes in refined carbohydrates. Foods carrying a high amount of refined carbohydrates not only include sweets and desserts, but also pastas, grains, and cereals. Diets rich in these foods can boost fructose consumption, increasing the risk for elevated blood lipids. This reduces the heart-protective effects of high-density lipoproteins, also known as HDL.
While the American public may be more aware of the negative effects of fat on their health, the impacts of high-fructose corn syrup seem lesser known. As public health alarms sound the negative effects of obesity, Americans are encouraged to diet and exercise while consumption of the major food additive continues at an increased rate. What better time, then, for research from such laboratories as those led by Joshua Wooten to shed new light on the health effects of high fructose?