Unless you have been living under a rock, you know that the rates of obesity in the U.S. population are dangerously high. The number of people who are significantly overweight has increased dramatically in the past 10 years. Perhaps the greatest concern is the skyrocketing rise in childhood obesity. Excessive body weight has secondary consequences, including higher risk of diabetes, heart disease and joint and respiratory problems. The quality of life is compromised when the ability to be physically active is reduced.Especially for young people, social interactions and relationships can be difficult when obese.

Given the dire statistics, it is natural to seek explanations for the obesity problem. How can we explain why obesity rates have risen so rapidly? Who is to blame for this problem? Assuming we can find the root of the problem, then we surely can fix it. At least 10 years ago, the USDA identified obesity as the primary health problem that needed to be researched, and the majority of nutrition grant funding since then has been targeted to obesity research. The top research labs in the country turned their focus on obesity. The number of articles with the word ‘obesity’ in them increased from 3,227 in 1989-1990 to 23,376 in 2008-2009. So you might think that in that time we would have figured out the cause and would have a solution to this obesity problem. Unfortunately that has not happened – in fact the number of obese people continues to increase.

So why is this happening? The human body is wonderfully efficient at capturing the energy in food. There is a direct relationship between energy consumption and body weight – if calorie intake exceeds calorie expenditure the excess is stored as fat. And the capacity to store fat is essentially unlimited. Food energy comes from three sources: carbohydrates, fats and protein. Although it is a somewhat more complex than that. When you consume more energy (in whatever form: carbohydrate, protein or fat) than you expend you will gain body fat – all forms of calories when eaten in excess will be converted to body fat. Conversely when calorie expenditure exceeds intake the body will consume fat and body weight is lost. Hence, the role of physical activity cannot be separated from food intake in the discussion of obesity. Look at some facts: we have more fitness programs, gyms and fitness centers than ever before, unlimited access to home fitness equipment, internet programs, running trails, and it seems as if every organization does a fun run or triathalon with huge numbers of participants. We have more access to opportunities for physical activity than in the past, yet obesity rates continue to rise. How can this be?

Some have raised the concern that the food supply is at fault. Despite the plethora of fat-free and sugar-free items in the food supply, society’s weight continues to increase. Some believe that the trend to lower fat intake (driven primarily by research that demonstrated high fat intake was linked to heart disease) may have caused a rise in obesity. Most nutritionists agree that a low fat diet would lower calorie intake because 1 gram of carbohydrate provides about half of the amount of energy as 1 gram of fat – so a low fat/high carbohydrate diet should be lower in total calories – therefore people would not gain as much weight. Unforeseen was the misunderstanding that developed among consumers that fat-free food was calorie-free food, which led them to over-consume calories. So, putting all the emphasis on fat was not the best public health message – because it failed to convey that total calories do matter.

Among the carbohydrates that have been targeted as a primary cause of obesity is high fructose corn syrup. HFCS was created by food scientists, and it is a very successful food ingredient because it gives foods so many positive attributes – soft textures, longer shelf-life, good mouth-feel and of course sweetness. So what is HFCS? Some basic chemistry is required. The starting material for HFCS is corn starch. Corn starch is simply chains of glucose. Glucose is the simplest unit of carbohydrate (a monosaccharide). If you have ever taken a big bite of corn starch, you might know that it isn’t very sweet at all. Food scientists converted some of the glucose in the starch to fructose (Recalling Chem 101: glucose is a 6 member ring monosaccharide and fructose is a 5 member ring monosaccharide – same number of carbons, so making the structural conversion can be done easily with enzymes – and this process occurs naturally in the human body). The result was a sweeter flavor because in our taste buds, fructose gives a much greater sweet response than glucose.

Before HFCS, the major sweetener used in foods was sucrose – the granular white crystals in your sugar bowl. Sucrose is a disaccharide comprised of glucose and fructose bound together. In fact, most HFCS has a similar ratio of glucose and fructose as found in sucrose – HFCS is either 40 or 55 percent fructose whereas sucrose is 50 percent fructose. Hence, the term ‘high fructose’ (which makes perfect sense to food scientists) is very misleading to consumers – chemically it is higher in fructose than untreated corn syrup, but it is really about the same as sucrose. In the digestive tract, sucrose is readily broken down by sucrase (an enzyme) to release glucose and fructose, both of which are absorbed and transported to the liver similarly. At the liver, fructose is converted to glucose (by an enzyme) which is then delivered to the body for use or stored as fat. Some research has shown that very high intake of fructose alone can cause problems at the liver because of the required extra steps to convert it into glucose – but under normal consumption patterns it would be impossible to reach that level of fructose intake. More facts about HFCS can be found at http://www.extension.iastate.edu/Publications/PM2061.pdf

So why the bad rap on HFCS? Does it cause obesity? Should you avoid it at all costs? The demonization of high fructose corn syrup (HFCS) was sparked in 2004 when Bray et al. published a widely read and much-quoted study in the American Journal of Clinical Nutrition. It noted the parallel between obesity and the rise in HFCS consumption, and hypothesized that the two could be related. The study prompted a massive reaction. One of the authors, Popkin, maintains he was just putting forward a theory that was intended to instigate further research. The majority of research since then has demonstrated that HFCS is not metabolized or converted into fat any differently than sucrose. There has been no viable explanation for how fructose (and not glucose) would be metabolized in a way that would lead to increased fat deposition, based on the well understood pathways of nutrient digestion, absorption and conversion to energy or storage as fat. In fact, in an exclusive interview with Caroline Scott-Thomas, Popkin said that he was wrong to single out high fructose corn syrup as largely responsible for obesity. “We showed later that fructose from sugar has the same effect,” Popkin said. “We were wrong in our speculations on high fructose corn syrup about their link to weight.”

However, a new study published in Pharmacology, Biochemistry and Behavior by Bocarsly. which has been widely quoted, stated that “these results suggest that excessive consumption of HFCS may contribute to the incidence of obesity”. This article was highlighted by Steve Adams in his editorial in the Iowa State Daily in March, as more evidence that HFCS is a major cause of obesity. A critical review of this research tells a different story and points out some of the problems nutrition scientists face when non-scientists write about science. Firstly, the study was published in a behavioral journal, therefore the reviewers were most likely not familiar with nutrition research – as a longstanding reviewer of research articles for nutrition journals. I can safely say this manuscript would not have been accepted by any of the top nutrition journals. The study design was significantly flawed due to a lack of direct comparison groups of HFCS and sucrose. The conclusion made by the authors that HFCS contributes to obesity is misleading and not based on the evidence provided by their experiments since the same effects were observed in the rats given sucrose for the same lengths of time. The authors ‘left out’ critical control groups to compare HFCS to sucrose directly in their key experiments. The study did show rats given access to HFCS in their drinking water along with their food gained more weight, had more body fat and higher triglycerides than rats given water without HFCS. This finding is not new, and it is simply evidence that calories are important and animals, like humans, will consume more energy than they need when presented with sweet and enjoyable foods, which willresult in a gain in body fat. The misleading concept presented by the authors is that HFCS caused different effects than sucrose or any other source of calories. That was in no way demonstrated by this study.

So what is the bottom line? The cause of obesity is well known, eat more calories than you use and you will gain weight. Does HFCS cause obesity? No. If you consume excessive calories from foods containing HFCS you will gain body fat, but that is equally true for any calorie-rich food. Will eliminating HFCS from the food supply eradicate obesity? No way. As we learned from the low fat era, targeting a single food ingredient doesn’t work. Blaming the food industry is misguided as well. Many ISU alums are employed by this industry and their primary goals are to produce safe, healthy and wholesome foods. Food scientists and nutritionists in these companies are hard at work every day creating new products that will have all the attributes consumers want – good taste, convenience and health, while allowing their company to make a profit (yes that is a necessary component of any business). Take a stroll through Hy-Vee and look carefully at the multitude of products, the vast majority of which, fit into a healthy diet. Can you find unhealthy foods in that same store, of course. Balance and moderation are needed. The only real solution to ending obesity is for individuals to become educated about the food they consume, how their body uses food, and how to balance their energy intake with their expenditure. Here at Iowa State there are many opportunities for you to become educated about food, nutrition and physical activity. We have leading academic and research programs in Food Science and Human Nutrition and Kinesiology, as well as one of the best College of Agriculture and Life Sciences in the world. Let’s make it our goal to integrate Science with Practice in all that we do – including our diets!

Ruth S. MacDonald, RD, PhD Professor and Chair Food Science and Human Nutrition.