Diabetes, Pregnancy, and COVID-19: Is High Fructose Corn Syrup the Root of the Problem?

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If you have been reading a lot of The Pulse, then you may know that type 2 diabetes mellitus is one of the main health conditions that elevates a person’s risk for developing life-threatening complications, if she develops COVID-19. You may also know that there are multiple connections between diabetes and pregnancy. Most diabetes occurring during pregnancy is categorized as gestational diabetes, diabetes that develops during pregnancy and then subsides after you deliver. Accounting for 90 percent of diabetes that is diagnosed during pregnancy, this type of diabetes puts a pregnant woman at risk of high blood pressure and serious pregnancy complication called preeclampsia, while putting the fetus at risk for high birth weight and size, and thus shoulder injury with nerve damage, if the baby is delivered vaginally. Pregnancy also can exacerbate pre-existing type 2 diabetes, a condition that puts the fetus at risk for still more health conditions, apart from high birth weight and shoulder injury. Since dietary sugar influences the course of diabetes, and since many food products feature labels announcing that they contain none of the sweetener known as high fructose corn syrup (HFCS), a question that comes up for pregnant women is whether HFCS is a factor in pregnancy health. Since the COVID-19 pandemic continues with no end in sight, we can also weave in the question of whether HFCS comes into play in terms of risk whether you are pregnant or not.

To delve into all of this, we need to unpack the story of HFCS in relation to diabetes, irrespective of pregnancy or COVID-19. To begin, we need to appreciate that there have been researchers studying the health effects of HFCS scientifically, while public discussion of the issue has also been influenced greatly by people and organizations objecting to HFCS as part of an ideological opposition to industrially farmed corn and genetic engineering. In recent years, such activism has led food companies to remove HFCS from an increasing number of processed foods, but only to replace it with sucrose (table sugar), creating the impression that the non-HFCS version of the food is healthier, when actually it is not. The most extreme example of such deceptive marketing is the use of “organic” cane sugar –a favorite additive of those who object to genetic engineering.

Introduced as a sweetener in the 1970s, HFCS is made in a process that begins with the extraction of starch from corn. Starch is a big molecule made of numerous molecules of glucose (the kind of sugar that circulates in your blood and the main fuel that your cells use for energy) connected like pieces of Lego®. Addition of an enzyme from bacteria disconnects the glucose molecules. Since water is also added, the process creates a glucose syrup. To make the corn syrup sweeter, another enzyme is added that transforms some of the glucose molecules into a slightly different sugar called fructose, which gets its name from its presence in fruit. While your body cells have enzymes that can convert fructose back into glucose, we are not well-equipped biochemically to handle an overwhelming influx of fructose. After absorption in the intestine, fructose arrives in the liver, where it is thought to increase the body’s resistance to insulin, the hormone that helps body tissues to absorb sugar from the blood. Insulin resistance gradually leads to type 2 diabetes –condition characterized by a rise in the concentration of blood sugar, despite the release of insulin into the blood.

The idea that high intake of fructose in the diet causes type 2 diabetes is supported by studies of laboratory animals. In these studies, animals fed pure fructose more easily developed diabetes compared with animals given the same amount of sugar calories in the form of sucrose, which is a molecular consisting of one glucose and one fructose molecule attached together, like having just two pieces of Lego® attached. Since laboratory animal studies also suggest that high intake of dietary fructose causes inflammation, and since the same type of inflammation is thought to be part of the disease process resulting from infection with SARS-CoV2 (the virus the causes COVID-19), there is some concern that the connection between diabetes and COVID-19 may relate to fructose.

This is the part where HFCS comes into the picture, but it’s also the part where the science ends and things get to be very speculative. Recall how we said earlier that HFCS is made when an enzyme converts some of the glucose of corn syrup into fructose, but note that we said some of the glucose. There actually are three main kinds of HFCS on the market, different mainly by the percentage of fructose in the mix. HFCS-42 contains 42 percent fructose, the rest being mostly glucose with a little bit of another sugar called maltose. HFCS-55 is 55 percent fructose, while HFCS-90 is 90 percent fructose, but it’s used mostly to mix with HFCS-42 to make HFCS-55. Most food that contains HFCS contains HFCS-42, the main exception being sodas, which often contain HFCS-55. How do these proportions compared with the fructose that caused diabetes in laboratory animals? That was pure fructose, which would be like HFCS-100, if there were such a thing, but recall that each sucrose molecule consists of a glucose molecule and a fructose molecule. In other words, sucrose is 50 percent fructose.

This means, in turn, that for any given amount of sugar, we should expect sucrose to be a little better than HFCS-55 (the HFCS in soda) but worse than HFCS-42, the most commonly added HFCS in other foods.

That’s right, you get more fructose from sucrose than you get from the most common type of HFCS in processed foods, which raises another question: Is there something different about the sucrose that makes it better than HFCS-42, despite supplying more fructose? Listening to staunch advocates of “organic” sucrose (sucrose from organic sugarcane) might lead you to think so. Often they point out that sucrose cannot release its fructose into the blood until an enzyme in your intestine, sucrase, breaks the molecule apart.

The problem with this reasoning is that sucrose actually is broken apart very rapidly after you ingest it, and, unlike a piece of fruit that contains fiber and various other agents that might lead your body to treat the fructose differently from the fructose in HFCS, the broken down sucrose has nothing else in it, just like a corn syrup. Consequently, in reviewing all available medical and scientific literature, the US Food and Drug Administration has not found that HFCS is any more dangerous than other sweeteners, which make perfect sense. After all, the fructose from sucrose –whether obtained from genetically engineered beats to make your ordinary table sugar, or from fancy organic sugarcane and put into little brown packages– is chemically identical to the fructose in HFCS.

And so, the take home message, is simple. A small dose of HFCS is healthier than a large dose of cane sugar. Rather than worrying about the form of the sugar that you ingest, focus on the amount. Keep it at a minimum.

David Warmflash
Dr. David Warmflash is a science communicator and physician with a research background in astrobiology and space medicine. He has completed research fellowships at NASA Johnson Space Center, the University of Pennsylvania, and Brandeis University. Since 2002, he has been collaborating with The Planetary Society on experiments helping us to understand the effects of deep space radiation on life forms, and since 2011 has worked nearly full time in medical writing and science journalism. His focus area includes the emergence of new biotechnologies and their impact on biomedicine, public health, and society.

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