Wednesday, January 1, 2014

Children of the Corn (Syrup): Is High Fructose Corn Syrup Actually Worse Than Sugar?

          In the United States, high fructose corn syrup (HFCS) is often used as a sweetener in place of cane sugar in both food and beverages.  Many consumers are concerned about the relative health effects of HFCS compared to sugar, and the increased consumption of HFCS in western nations such as the US is associated with a greater prevalence of poor health outcomes such as type II diabetes.  This concern has caused a recent campaign to replace HFCS with cane sugar in popular foods and beverages, such as the increase in popularity of HFCS-free Mexican Coke.  As with Genetically Modified Organisms, health fears over HFCS have created an irrational fervor among the general public, even among educated individuals.  I have therefore attempted to provide a (mostly) unbiased, rational summary of existing data on the subject to promote better-educated personal decisions on dietary choices.

General Background on HFCS
The chemical process for creating HFCS was first invented in 1957 and was later optimized for industrial scale production by Dr. Yoshiyuki Takasaki in the late 1960s-1970.  HFCS is now the leading sweetener (and #1 source of calories) in the US due to many factors, including tariffs on foreign sugar, subsidies to corn farmers, and industrial benefits of its liquid state.  HFCS is produced by isolating glucose-rich corn syrup and  enzymatically converting some of the glucose into fructose. Two primary types of HFCS exist: HFCS-42 (42% fructose/53% glucose) and HFCS-55 (55% fructose/42% glucose).  HFCS-55 is typically used in soft drinks and other beverages, while HFCS-42 is often used in processed foods and baked goods.  It is important to note that despite the name, HFCS in both forms maintains close to a 50% ratio of fructose, similar to that in sucrose (with glucose) and honey (with dextrose).  Fructose and glucose exist independently together in solution as HFCS while sucrose contains covalently linked glucose and fructose molecules that are only separated upon metabolism.

Research Studies
          One of the most cited studies suggesting a relationship between HFCS consumption and negative health outcomes was published by Bray et al in 2004, which stated that “the increased use of HFCS in the United States mirrors the rapid increase in obesity”.  The study also claimed that fructose is metabolized differently than glucose, leading to increased fat production in the liver and reduced insulin release.  Additionally, reduced insulin levels decrease secretion of leptin (in agreement with another paper), which induces satiety and restricts hunger.  In strong criticism of these conclusions was a sternly worded report debunking the association between obesity and HFCS.  The report argued that increased overall caloric intake is more likely the cause of increasing obesity rates, evidenced by the fact that HFCS use in the US has actually remained stable over the past 15 years despite ever increasing obesity rates, while the ratio of HFCS consumption does not actually correlate with obesity worldwide (Figure 1).

(John White, Am J Clin Nutr 2008)

Another recent study determined that rats gained substantially more weight when HFCS was included in their diet as compared to sucrose or control diets.  Even more striking, it was found and later confirmed that glucose and fructose have opposite metabolic effects on the hypothalamus.  Glucose produces a corresponding reduction in food intake inducing satiety while fructose in contrast stimulates an increase in food intake.  A 2013 report utilized MRI to further validate these findings, confirming differential effects between fructose and sucrose on satiety and insulin response. Critics of this data point out however that the first study injected sugar directly into the brain of rats (obviously unrelated to human ingestion), and while the second study did use bloodstream injection instead, the concentrations utilized were way too high to be considered physiologically relevant.  Nonetheless, while the true significance of this effect on human consumption is debatable, it does appear clear that fructose and glucose are indeed metabolized differently and therefore may have legitimate differential effects on nutrition.

Like many health debates, the discussion over HFCS is a complicated, with evidence both for and against negative health effects from ingesting HFCS over glucose or sucrose.  One confusing issue is the difference between fructose and HFCS.  As previously mentioned, HFCS only contains 42-55% fructose, with glucose making up the difference, while sucrose is 50:50 fructose:glucose (covalently linked together).  While many studies indicate definite differential effects of pure fructose and glucose on metabolism and hypothalamic response, it is difficult to determine how this relates to the effects of HFCS specifically.  I was able to find a thorough paper that directly assessed the effect of glucose:fructose ratio on various nutritional outcomes in young men including appetite, food intake, free blood glucose levels and plasma insulin levels among others.  In agreement with previous studies, high-glucose solutions significantly reduced food intake and appetite and high-fructose solutions resulted in increased caloric intake.  Sucrose did appear to have a somewhat stronger effect on satiety and insulin stimulation than HFCS-55 or 50:50 solution, however these differences were not overall statistically significant.  The authors therefore conclude that large differences in fructose:glucose ratios do result in strong metabolic variation, but that HFCS, sucrose and 50:50 solution all have “similar effects on physiological measures”.

As I have shown, there are an abundance of studies attempting to discern the metabolic differences between HFCS and sugar, however current evidence remains inconclusive.  A report from the Center for Food, Nutrition and Agriculture Policy determined that existing data is “insufficient to implicate HFCS per se as a causal factor in the overweight and obesity problem in the United States.” In agreement, the American Medical Association stated that HFCS and sucrose are metabolically very similar and also agreed that current evidence was not indicative of any substantial health risks from ingesting HFCS instead of sucrose.  Both organizations agree that research is clearly needed in order to determine the true effect of HFCS on health outcomes compared to other sugar solutions.  In the meantime, it is fair to assume that HFCS, sucrose, honey, and other natural sweeteners all have a similar effect on health and metabolism.  Stick to the old adage of having everything in moderation, and you can save your money and not worry about having to buy foreign soda.

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