Eating More Fructose Than Nature Intended Is Also Probably a Bad Idea
I recently read an article about a study that supposedly found that high-fructose corn syrup had a different effect on the body than did “regular sugar.” This made little sense, because high-fructose corn syrup is only slightly higher in fructose than table sugar is. In fact, the study said exactly nothing about any difference between table sugar and high-fructose corn syrup. On the other hand, it did say that drinking a lot of sugar water can make you gain weight really fast.
During digestion, table sugar is rapidly broken down to a 50:50 mixture of two simple sugars: glucose and fructose. High-fructose corn syrup is a 45:55 mixture of glucose and fructose. Not much difference. However, the study wasn’t a comparison of high-fructose corn syrup versus what an ordinary person would think of as “regular sugar,” it compared huge doses of pure fructose to huge doses of pure glucose—a major difference. In reality, the study showed three things. First, people can gain weight really fast if they drink a huge amount of watery syrup, which provides a lot of calories while doing very little to satisfy the appetite. Second, a calorie is a calorie. People gain weight just as effectively if they get extra calories from fructose or glucose. Third, fructose has different effects on the body’s metabolism than glucose has, but we already knew that. None of these results were surprising, so none of the findings of this study were actually newsworthy to the general public. The journalists who wrote about this story made it sound newsworthy by misinterpreting it.
Thanks to the magic of the Internet and the National Library of Medicine, I was able to find the actual article for myself. The subjects in the study first spent two weeks in a clinical research center, eating “an energy-balanced, high–complex carbohydrate (55%) diet.” Of course, 55% of calories from complex carbohydrates isn’t “high” in complex carbohydrates by my standards, but so what? After spending two weeks eating the controlled diet, the subjects were sent home for an eight-week outpatient study, in which they were allowed to eat whatever they wanted, as long as they drank enough of a sweetened beverage to give them 25% of their calorie requirements. Some of the subjects were given a beverage sweetened with pure fructose (not high-fructose corn syrup), the others were given a beverage sweetened with glucose.
As a result of guzzling all that sugar water, the people in both groups took in more calories than they needed. In fact, people in both groups took in roughly the same number of extra calories and gained roughly the same amount of extra weight as a result. That wasn’t surprising, although it was interesting that the extra fat tended to get deposited in different places, depending on which kind of sugar was consumed. Nor was it surprising that the fructose beverages caused spikes in the amount of fat (triglycerides) in the blood after meals. Scientists already knew that fructose does that. They’ve also known for decades that high levels of fat in the blood contribute to insulin resistance, which in fact occurred among the people who drank all that extra fructose.
Although the study does suggest that eating too much fructose can be bad for you, it didn’t say anything about whether high-fructose corn syrup was significantly worse than table sugar. In fact, a commentary that accompanied the article said, “It is not known whether the adverse effects of sucrose and HFCS consumption are ‘diluted’ by their lower fructose content relative to pure fructose.” The commentary does make it clear that if you are eating too much fructose, you probably aren’t getting it from eating too much fruit. “One would have to eat vast quantities of fruits every day in order to ingest metabolically adverse amounts of dietary fructose.”
The take-home message for consumers wasn’t clear from the news accounts, but it’s very simple. It’s hard to overdose on fructose from eating fruit, but drinking syrup-water isn’t good for you.