Obesity is on the rise, and we don’t seem to be content with the obvious reasons: We eat more empty calories and we move our bodies a lot less than any generation before ours. In our personal responsibility-averse culture, we decided there must be something sinister going on. So we looked really hard and, sure enough, we found it. Call it the “high-fructose corn syrup plot.”
High-fructose corn syrup (HFSC) has found its way into all kinds of foods formerly sweetened with sugar (sucrose): carbonated beverages, baked goods, canned fruits, jams, jellies and dairy products. It swiftly became the major source of fructose in the U.S. Once inside our bodies, the story goes, HFSC is turned into fat more easily than “regular” sugar and the result is that big collective push over the obesity cliff.
But now, many experts are beginning to question the recent trend of beating up on HFSC. Its reputation as a fat promoter has likely been overstated, and it is no more a culprit in the epidemic of obesity than any other refined sugar.
The FDA had earlier come to its defense, claiming, “High-fructose corn syrup is as safe for use in food as sucrose, corn sugar, corn syrup and invert sugar.” And with this Big Government nod of approval, the battle lines were drawn.
Most of us are familiar with corn syrup, generally via pancakes. When I was a kid, we bought it because it was cheaper than the natural syrups that were our favorites: maple, sorghum and honey. Corn syrup is made from corn starch by a series of three enzymatic reactions. The result is a syrup that consists mostly of glucose (which stands to reason because starch is a chain of glucose molecules).
|High-fructose corn syrup is 55 percent fructose, 45 percent glucose, vs. table sugar, which is 50-50 fructose-glucose. Image courtesy of hfcsfacts.com.
High-fructose corn syrup is made from the same corn starch, but by a slightly different enzymatic process developed in 1970. An isomerase converts much of the glucose into fructose – about 42 percent. Further processing and filtering results in a 55 percent fructose final product. By contrast, sucrose is 50 percent fructose.
And that’s where the anti-HFCS camp gets to skate; the “high” is in comparison to old-fashioned corn syrup, not in comparison to table sugar. To be straightforward, there is a chemical difference, in that the fructose in HFCS is “free,” whereas in sucrose it’s bound to glucose.
Manufactures favor HFCS because it’s cheap, sweeter than sugar, more stable than sugar and can be labeled “all natural.” But does fructose make us fat?
The problem, according to a 2004 study by S. J. Nielsen, Ph.D., and B. M. Popkin, Ph.D., reported in the American Journal of Clinical Nutrition, is that fructose is digested, absorbed and metabolized differently than glucose and that difference may lead to obesity.
That conclusion is based on two lines of reasoning: Fructose is more easily converted to fat than glucose (so eating the same amount of calories will make you fatter), and fructose is less satisfying than glucose, hence you will eat more.
Inside the cell, fructose is converted to fructose-1-phosphate, whereas glucose is converted by glycokinase to glycose-6-phosphate, which means that it’s a little easier for fructose to become glycerol, the backbone of triglycerides and phospholipids. This is a fancy way of implying that because different sugars follow slightly different metabolic pathways, their respective calories are utilized in a significantly different manner, something that nutritionists have rejected since…forever.
Here’s a little background. In 2000, R. M. McDevitt, Ph.D., (American Journal of Clinical Nutrition) overfed subjects in a metabolically controlled setting with total calories fixed and found no difference in the distribution of excess calories as fat regardless of whether that excess was from glucose, fructose or sucrose.
The second line of reasoning, that fructose is not as satisfying as glucose, is more interesting. Glucose stimulates insulin production. Fructose does not, at least not as much. (Fructose also doesn’t enter the brain; glucose does.) Insulin can reduce our desire to eat, either directly by its effect in the brain, or indirectly by increasing leptin release by fat cells in a delayed response. Leptin is a hormone that may signal the brain that the body is sufficiently fat, so there is no need to continue eating. Hence the low insulin concentration from ingesting fructose yields a lower average leptin concentration, which would induce us to eat more.
In other words, by the exact mechanism low glycemic foods are supposed to keep us thin, fructose is supposed to make us fat. In this instance, insulin – the “fat storage hormone” – provides the mechanism that prevents us from overeating.
This is the opposite of what high-glycemic foods are supposed to do. (Fructose has a glycemic index lower than most, if not all, beans, and certainly lower than whole grains.) But wait a minute: The current trend says we should fear high glycemic-index foods because they stimulate insulin and wear out the pancreas. In making the case against HFCS, we skip over the conflict between fructose metabolism and glycemic index.
The concern over the explosive increase in our use of HFCS generally ends with a warning about our excessive consumption of sweetened soft drinks. Some studies indicate our bodies don’t recognize sugary soft drink calories well enough to compensate naturally through eating less. But there is as yet no evidence that it matters what the sweetener is.
It seems with respect to obesity and carbohydrates, we go from one extreme to the other, warning about potatoes because of their high glycemic index, and fructose because of its low glycemic index, sending insulin from bad guy to good guy, from the fat-storage hormone to the regulator of a healthy appetite.
Nutritionally, refined carbohydrates (sweeteners) should account for no more than 10 percent or so of our daily calories. Presently, added sweeteners account for 16 percent of dietary calories for the average American. That’s about 320 calories of nothing but added sugar, not to mention the calories from refined starches and fats.
The problem isn’t which sweetener we overindulge in, it’s basic math: Four calories per gram is still four calories per gram, at least until proven otherwise.