In the early 1980s, public health authorities began warning that saturated fat was driving obesity and various degenerative diseases. During this same period, high-fructose corn syrup (HFCS) rose to prominence, sneaking itself into processed foods, especially sodas, cookies, and cakes.
Saturated fat consumption fell. Sugar consumption and overall caloric intake rose. Obesity, metabolic syndrome, type-2 diabetes, and other diet-related diseases got worse. These disturbing facts have prompted nutrition scientists to begin investigate fructose (a primary type of sugar) as a possible driver of the obesity crisis.
Does fructose uniquely promote overeating? Does fructose affect satiety differently than other sugars, particularly glucose?
Before looking into these questions, we should note that fructose is almost always accompanied by glucose in natural foods. The following chart, for example, shows the sugar content of common foods.
Almost all foods containing sugars, including vegetables, include both glucose and fructose (as well as sucrose, which is 50% fructose and 50% glucose). The ratio of fructose to glucose for most foods hovers around 50:50 and generally never exceeds 70:30.
It’s been suggested that high-fructose corn syrup is more dangerous than table sugar because it contains proportionally more fructose, a modest 55% compared to 50% for ordinary table sugar. According to the numbers in the chart, if fructose were inherently more dangerous than glucose, we would have to conclude that apples and pears are worse than bananas and blueberries.
So is there any evidence that fructose promotes overeating? Is snacking on apples rather than bananas a bad idea? In 2013, a study published in the Journal of the American Medical Association sparked headlines like, “Fructose changes brain to cause overeating, scientists say,” and “Revealed: fructose ‘may spur overeating.’”1, 2
From the actual study, we read, “Glucose but not fructose ingestion reduced the activation of the hypothalamus, insula, and striatum—brain regions that regulate appetite, motivation, and reward processing; glucose ingestion also increased functional connections between the hypothalamic-striatal network and increased satiety.”3
It seems convincing. But was this study representative of real-world scenarios? Let’s see how the study was organized. The scientists worked with 20 normal-weight subjects (10 men, 10 women) without diabetes and a mean age of 31. The study was a blinded, random-order crossover design (so far so good).
Following an overnight fast, subjects drank 300ml of cherry-flavored water with either 75g of fructose or 75g of glucose. 60 minutes later, blood samples were drawn and the subjects completed a series of surveys rating “feelings of hunger, satiety, and fullness on a scale of 1 to 10.”
First of all, 75g of sugar, whether fructose or glucose, is an inordinately large amount to consume at one time. Roughly equivalent to 2.5 cans of soda, this might not be reflective of real-world consumption patterns. More importantly, however, we never consume foods or beverages sweetened entirely by fructose or by glucose. Invariably, both sugars are present, typically in 50:50 ratios.
This study made headlines because it contradicted previous studies. A 2007 study, for example, tested energy balance and satiety of high-fructose corn syrup (55% fructose, 45% glucose) compared to sucrose (50% fructose, 50% glucose). The scientists found that glucose and fructose contribute to satiety through different biochemical mechanisms, but overall there are no significant differences between sucrose- and HFCS-sweetened drinks with respect to satiety and energy balance.4
Ultimately, the fructose/overeating issue comes down to quantity and form (whole foods versus liquids). Fructose appears to have bidirectional effects. In other words, effects on certain biomarkers (fasting triglycerides, insulin sensitivity, etc.) at moderate doses may be absent or even opposite those observed at very high/excessive doses.5
Very high/excessive doses are almost certainly detrimental, but moderate doses, especially when consumed as whole foods, can be very beneficial. Researchers from the Harvard School of Public Health, for example, determined that consumption of whole fruits, particularly blueberries, grapes, and apples, is associated with decreased type-2 diabetes risk, whereas consumption of fruit juice is associated with increased risk.6
THE BOTTOM LINE
Foods containing fructose, especially fruits and vegetables, are healthy when consumed as part of a balanced Paleo diet. Eating a couple pieces of fruit each day doesn’t promote overeating, but drinking 4 cans of soda or fruit juice might. More research must be done to better understand fructose, but when you read that fructose is dangerous, ask about the quantity, source, and form (liquid/whole food) of fructose. Also keep in mind that glucose almost always accompanies fructose in real foods, so studies on pure fructose consumption may not be relevant to real-world eating.
Christopher James Clark, B.B.A. is an award-winning writer, consultant, and chef with specialized knowledge in nutritional science and healing cuisine. He has a Business Administration degree from the University of Michigan and formerly worked as a revenue management analyst for a Fortune 100 company. For the past decade-plus, he has been designing menus, recipes, and food concepts for restaurants and spas, coaching private clients, teaching cooking workshops worldwide, and managing the kitchen for a renowned Greek yoga resort. Clark is the author of the critically acclaimed, award-winning book, Nutritional Grail.
 CBS/Associated Press. (January 2, 2013). Fructose changes brain to cause overeating, scientists say. CBS News. Retrieved from //www.cbsnews.com/news/fructose-changes-brain-to-cause-overeating-scientists-say/
 Associated Press. (January 2, 2013). Revealed: fructose ‘may spur overeating.’ The Independent. Retrieved from //www.independent.co.uk/life-style/health-and-families/health-news/revealed-fructose-may-spur-overeating-8434959.html
 Page, KA., et al. (January 2, 2013). Effects of Fructose vs Glucose on Regional Cerebral Blood Flow in Brain Regions Involved With Appetite and Reward Pathways. Journal of the American Medical Association, 309(1). Retrieved from //jama.jamanetwork.com/article.aspx?articleid=1555133
 Soenen, S., et al. (December 2007). No differences in satiety or energy intake after high-fructose corn syrup, sucrose, or milk preloads. American Journal of Clinical Nutrition, 86(6). Retrieved from //ajcn.nutrition.org/content/86/6/1586.full
 Livesey, G. (April 22, 2009). Fructose Ingestion: Dose-Dependent Responses in Health Research. The Journal of Nutrition, 139(6). Retrieved from //jn.nutrition.org/content/139/6/1246S
 Muraki, I., et al. (August 29, 2013). Fruit consumption and risk of type 2 diabetes: results from three prospective longitudinal cohort studies. British Medical Journal, 347. Retrieved from //www.bmj.com/content/347/bmj.f5001