Health concerns have been raised about high fructose corn syrup regarding its potential to cause obesity, cardiovascular disease, diabetes, and non-alcoholic fatty liver disease, and its containing of traces of mercury.
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HFCS has become an increasingly common food ingredient in the last 40 years; however, concerns have been raised that, compared to other caloric sweeteners, HFCS consumption increases the risk for obesity and other adverse health outcomes.
In 2009 The American Medical Association reviewed the existing studies and concluded that because the composition of HFCS and sucrose is similar it appears unlikely that HFCS contributes more to obesity or other conditions than sucrose, and at the present time there is insufficient evidence to ban or otherwise restrict use of HFCS or other fructose-containing sweeteners or to require the use of warning labels on products containing HFCS. They caution that there have been few studies to evaluate the potentially differential effect of various sweeteners, particularly as they relate to health conditions such as obesity which develop over relatively long periods of time.[1] The most commonly used types of HFCS (HFCS-42 and HFCS-55) are similar in composition to sucrose (table sugar), consisting of about equal amounts of fructose and glucose. The primary difference is that these monosaccharides exist free in solution in HFCS, but in disaccharide form in sucrose. (The enzyme sucrase, secreted in the small intestine of most humans, breaks down sucrose into fructose and glucose before it enters the blood stream.)
A 2006 systemic review of the relationship between sugar-sweetened beverages and obesity found: "The weight of epidemiologic and experimental evidence indicates that a greater consumption of sugar-sweetened beverages is associated with weight gain and obesity. Although more research is needed, sufficient evidence exists for public health strategies to discourage consumption of sugary drinks as part of a healthy lifestyle.[2]
Bocarsly et al.[3] completed a 2010 study using two experiments with rats. First, groups of 10 rats were given water sweetened with either 8% HFCS 12 hrs/day, 8% HFCS 24 hrs/day, or 10% sucrose 12 hrs/day (table sugar), all with ad libitum rodent chow, or only ad libitum rodent chow for a duration of 8 weeks.
For the second experiment:
Over the course of 6 or 7 months, "both male and female rats with access to HFCS gained significantly more body weight than control groups. This increase in body weight with HFCS was accompanied by an increase in adipose fat, notably in the abdominal region, and elevated circulating triglyceride levels. Translated to humans, these results suggest that excessive consumption of HFCS may contribute to the incidence of obesity". The study found that rats consuming rat chow with HFCS gained 48% more weight than rats that only consumed rat chow.[4]
The study was widely criticized by food science experts, most notably Marion Nestle, a professor in the Department of Nutrition, Food Studies and Public Health at New York University. In her blog entry about the study, she argued that the study was poorly designed and carried out and did not provide convincing evidence of a difference between the effects of HFCS and sucrose on the body weight of rats. "I can hardly believe that Princeton sent out a press release yesterday announcing the results of this rat study...How they came to these conclusions is beyond me."[5][6][7] Bocarsly responded: "What we did in the lab was what was most interesting scientifically. We're a behavioral neuroscience lab, so what we're interested in finding is how these foods affect your brain chemistry. We hope this is the first step in a long series of research."[8]
A 2004 study investigated the relationship between mass intake of high-fructose corn syrup and the development of obesity. The authors concluded that since unlike glucose, fructose does not stimulate insulin secretion or enhance leptin production which signal the regulation of food intake and body weight, dietary fructose may contribute to increased energy intake and weight gain.[9] The study's lead author, George A. Bray, noted that fructose absorbed from large amounts of regular sugar and from high-fructose corn syrup elicit nearly equivalent responses in the body.[10] One of the study coauthors, Dr. Barry M. Popkin, told The New York Times: "I don't think there should be a perception that high-fructose corn syrup has caused obesity until we know more."[11]
According to Ferder, Ferder & Inserra, (2010) fructose consumption and obesity are linked because fructose consumption does not cause an insulin response. This is important because, without an insulin response after consumption of a high-fructose food, there is no suppression of appetite, which is normally induced by hyperinsulinemia after a meal. If satiety or suppression of appetite does not occur, then the person will continue eating or overeating as the case may be. This is linked with obesity because excess calories are converted and stored as fat, and when this process continues over a long period of time it results in obesity. The article concludes, however, that sucrose (table sugar) and high-fructose corn syrup elicit similar short-term responses. It is important to note that sucrose is a disaccharide composed of one glucose molecule and one fructose molecule. High-fructose corn syrup is similar in composition, but rather than existing in a bond, fructose and glucose exist separately. [12][13]
A 2008 study in humans (supported in part with funding from Pepsico, Inc., the USDA, and the American Diabetes Association) analyzed the circulating levels of glucose, insulin, leptin, ghrelin, and triacylglycerol during a 24 hour period after consuming drinks containing HFCS or sucrose. The researchers concluded that the consumption of HFCS or sucrose did not yield differing metabolic effects.[14] Several studies funded by Tate & Lyle, a large corn refiner, the American Beverage Institute and the Corn Refiners Association,[15][16] have defended HFCS. Forshee et al. concluded "that HFCS does not appear to contribute to overweight and obesity any differently than do other energy sources."[17] Monsivais et al. (2007) compared the effects of isocaloric servings of colas sweetened with HFCS 42, HFCS 55, sucrose, and aspartame on satiety and subsequent energy intake.[18] They found that all of the drinks with caloric sweeteners produced similar satiety responses, and had the same effects on subsequent energy intake.
A 2007 meta-analysis done by Forshee et al and funded by Tate & Lyle, a large corn refiner that makes HFCS, argued that although there is valid information regarding fructose and its role in promoting obesity, there is no concrete and conclusive research to support the hypothesis that high-fructose corn syrup has the same obesity promoting properties as fructose. Although there are many studies that link fructose and obesity, there are very few studies that evaluate the relationship between HFCS and body weight increase or increased BMI. The only data that does link HFCS with obesity or weight gain comes from epidemiological data which is recognized as an insufficient source for the development of a true cause and effect relationship between HFCS and obesity. Though there is no current research that links HFCS consumption to obesity, further research is needed on the subject in order to form an experimentally supported theory either supporting or refuting this hypothesis.[19] [20] The review has been criticized for using incorrect methodology. Noting that a previous systematic review and meta-analysis on the same topic reported “clear associations of soft drink intake with increased caloric intake and body weight”, it was suggested that the reasons for the discrepant results between Forshee et al and others stem from analytic errors in their review.[21]
However, some studies do link consumption of HFCS and obesity. The Corn Refiners Association launched an advertising campaign to counter these criticisms, claiming that high-fructose corn syrup is natural since it's "made from grain corn" and "is nutritionally the same as honey and table sugar".[22]
A pilot study reported that some high-fructose corn syrup manufactured in the U.S. in 2005 contained trace amounts of mercury. The mercury appeared to come from preparations of sodium hydroxide and hydrochloric acid, two chemicals used to produce high-fructose corn syrup. These chemicals may have come from plants also specializing in industrial chlorine chlor-alkali using the mercury cell Castner-Kellner process, and may contain traces of mercury if this specific process is utilized. Mercury concentrations in the samples testing positive ranged from 0.012 μg/g to 0.570 μg/g (micrograms per gram). Nine of the twenty samples tested did contain measurable amounts of mercury.[23]
The Corn Refiners Association has questioned whether the mercury found was in dangerous levels or forms.[24]
According to the American Heart Association, metabolic syndrome is defined as the manifestation of numerous metabolic risk factors in one individual. These risk factors include high blood pressure, abdominal fat, high blood triglyceride levels, high uric acid levels, insulin resistance and a state of chronic inflammation. Individuals with metabolic syndrome are at a high risk for developing other related health issues such as cardiovascular disease and type 2 diabetes. [25] Metabolic syndrome is becoming increasingly prevalent in the United States; it is estimated that over 50 million Americans have this condition. Due to the increased prevalence of this condition in recent years it is hypothesized that metabolic syndrome is linked to overconsumption of high-fructose corn syrup. [26] Similar to the research cited that claims a link between high-fructose corn syrup and obesity, the research that speaks to metabolic syndrome focuses mostly on the fructose aspect of high-fructose corn syrup. According to Nseir, Nassar and Assy (2010), the onset of metabolic syndrome is triggered by visceral adipose tissue which is linked to the consumption of fructose. Fructose is related to adiposity through the increase in blood triglyceride levels caused by the consumption of this monosaccharide. This increased adiposity leads to both obesity and metabolic syndrome. [26] According to Ferder, Ferder and Inserra (2010), a high-fructose diet induces inflammation and metabolic syndrome. In a study they performed on rats, the addition of 10% wt/volume fructose solution to the rat’s diet increased the inflammatory response in rats as well as the prevalence of metabolic syndrome in the experimental groups. Although this research has not been performed on human subjects, the researchers believe that this study is a good indicator of relevance of the hypothesis that increased fructose intake leads to metabolic syndrome. [13] Forshee et al. (2007), states that although this research is valid for fructose consumption, it is not a good representation of the effects of HFCS as related to metabolic syndrome. This condition is closely linked with obesity, and both conditions cannot be correlated with the intake of high-fructose corn syrup without further research.[20]
The Mayo Clinic defines cardiovascular disease as an umbrella term used to describe a wide variety of conditions affecting the heart. Currently, cardiovascular disease is the number one cause of death in the world as well as in the United States. [27] One of the causes of cardiovascular disease is believed to be the consumption of high-fructose corn syrup. According to Parrish (2010), the metabolic processes involved in the breakdown of fructose can lead to a build up of uric acid. A build up of uric acid is one of the symptoms of metabolic syndrome which is a risk factor for cardiovascular disease. Parrish also references the link between fructose and blood triglyceride levels as a risk factor for cardiovascular disease, specifically atherosclerosis. [28] According to Brown, Dulloo and Montani (2008), studies performed on animals have shown a link between sugar intake and cardiovascular disease, specifically hypertension, tachycardia and ventricular hypertrophy. In these studies, glucose was shown to be unrelated to hypertension, whereas fructose was shown to be the more damaging sugar component. An 8% solution of fructose was shown to induce left ventricle hypertrophy, hypertension and tachycardia, within a week of its substitution for drinking water, in populations of rats. Although these studies proved that overall sugar consumption due to the fructose component of sugar is linked with cardiovascular disease, they do not produce evidence that HFCS is more responsible for these relationships than sucrose or other sugars. [29]
According to Brown, Dulloo and Montani, fructose consumption is linked to the onset of insulin resistance and type 2 diabetes (2008). In healthy individuals after two weeks on a high-fructose diet, a 25% reduction in insulin sensitivity was seen. Researchers believe that the relationship between HFCS and insulin resistance is dose dependent based on the fructose content, because in individuals who were given 3g of fructose per kg of body weight per day insulin resistance was observed, however a lower dose of fructose (1.5g per kg of body weight per day) did not produce the same insulin resistance. This research shows that limited sugar consumption (specifically the fructose component) does not lead to the onset of insulin resistance or diabetes, however higher amounts of sugar consumption is believed to lead to both insulin resistance as well as type 2 diabetes. [29] Chi-Tang Ho et al. found that soft drinks sweetened with HFCS are "astonishingly high" in harmful carbonyl compounds, such as methylglyoxal, when compared to a diet soft drink control, and concluded that sucrose does not have the same tendency to produce these compounds. According to the author, reactive carbonyls also are elevated in the blood of individuals with diabetes and linked to the complications of that disease. Based on the study data, the author estimates that a single can of soda contains about five times the concentration of reactive carbonyls than the concentration found in the blood of an adult person with diabetes.[30] However, many other foods contain much higher levels of reactive carbonyls, such as cheese, coffee and toast.[31]
According to Allocca and Selmi (2010), Non-alcoholic fatty liver disease (NAFLD) is defined as “the hepatic manifestation of the metabolic syndrome and is currently among the most prominent causes of chronic liver disease in the United States, being found in up to 30% of the general population.” One of the main contributing factors to NAFLD is insulin resistance or an excessive intake of carbohydrates or fats leading to an elevation in blood glucose, insulin and triglycerides. [32] Mariangela Allocca and Carlo Selmi (2010), state that unlike the previously discussed conditions where research is primarily focused on the fructose component of HFCS or sucrose, NAFLD is related to both the fructose and the glucose components of both sugars. First, fructose is linked with NAFLD through an elevation in fructose consumption producing elevated blood triglyceride levels. As chronically elevated blood triglyceride levels are one of the main factors contributing to risk for NAFLD, so high-fructose consumption, which produces these elevated levels, is also a risk factor for NAFLD. Animal studies, specifically those performed on fructose-fed mice, have shown that chronic fructose consumption leads to lipid accumulation in the liver. “The available experimental and human data strongly support the notion that fructose avoidance should be encouraged in the prevention and treatment of NAFLD.” [32] According to Allocca and Selmi (2010), glucose consumption is a key factor in the development in NAFLD as well as fructose. Glucose plays a role in the development of this condition because blood glucose concentrations that travel to the liver can either be converted to glycogen or free fatty acids. Glucose is converted to free fatty acids in the liver in the process of insulin-stimulated de novo lipogenesis, which results in the accumulation of these lipids in the liver. This build up of lipids in the liver leads to increased production and secretion of very low density lipoprotein (VLDL) which eventually results in an inability to prevent NAFLD through problems maintaining fat balance. Although, NAFLD involves both the glucose and the fructose components of HFCS, there has been no conclusive research linking HFCS consumption to the onset of NAFLD more so than sucrose or other sugar consumption. [32]
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