The Molecular Structure of Fructose
Does that look like something you should be eating?

Let’s face it. Eventually, we all want something sweet. So when you do decide to make dessert at home, what sweetener should you reach for? What should you put in your coffee? We all know that it shouldn’t be anything with high-fructose corn syrup because, so we’re told, that high level of fructose will mess you up and make you fat. But just how much worse for you is high-fructose corn syrup than sugar? Or honey? It’s time for a science lesson.

There are five sugars known as monosaccharides: glucose, fructose, galactose, xylose, and ribose.(1) These five sugars serve as the building blocks of the disaccharides that we all know and love: sucrose, lactose, maltose, trehalose, and cellobiose.(2) We’re going to focus specifically on two of the monosaccharides, glucose and fructose, and one of the disaccharides, sucrose.

Glucose is the main energy of cellular function, metabolized by most every cell in the body. It fuels your cells, and while not technically necessary for the body to function (it can operate on fuel derived from fat and protein), some level of glucose from carbohydrates is a nice to have, especially if you engage in high-intensity activity. The body works very hard to keep blood glucose in a narrow range, through careful administration of insulin. Too high and all kinds of damage can be done, too low and all kinds of death can occur. So really only one kind of death, but in the grand scheme, isn’t one enough?

Fructose is a sugar found mainly in fruits, which undergoes metabolic processing in the liver. The main problem with fructose is that little piece about needing to be metabolized by the liver. Studies have suggested that consuming too much fructose messes up all kinds of things in the body.(3) Some show a correlation with obesity. Fructose tends to promote an increase in triglycerides in the blood, which are a definite marker for heart disease. Other studies have shown that fructose pulls important minerals from the blood, chelating them out of the body. This little gem also increases levels of uric acid in the body, an abundance of which brings about the symptoms of gout. Studies have shown fatty liver disease from too much fructose, making the liver look like that of an alcoholic. And finally, fructose reduces circulating insulin, leptin, and ghrelin levels, hormones which control satiety and appetite.

So seeing that fructose may be the detrimental factor in sweeteners, it seems that our goal should be to reduce the fructose content as much as possible. Let’s compare some different types of sugar added to common products. First, there’s high-fructose corn syrup, which is “available” in three different formulations: HFCS-90, HFCS-55, and HFCS-42.(4) HFCS-55, the type most commonly used in soft drinks, is 55% fructose and 45% glucose. HFCS-42, used most often in baked goods, is 42% fructose and 58% glucose. HFCS-90 is used almost exclusively to produce the other two types. HFCS is the bane of humanity, according to most nutritionists, responsible for everything from the obesity epidemic to Hitler’s invasion of Poland.

Then there’s sucrose, comprised of 50% fructose and 50% glucose. The weak bond between the two monosaccharides is cleaved in a weakly acidic environment. Since the stomach is a highly acidic environment, you can see that sucrose doesn’t stand a chance and each molecule of sucrose eaten yields a molecule of glucose straight to the blood and one of fructose straight to the liver. Obviously that isn’t much of an improvement over the 55% fructose content of HFCS and is actually worse than the HFCS-42 used in baked goods. But you’ll not hear that because it doesn’t make a good sound bite.

Most often, I hear people talking about avoiding products with HFCS or sugar and opting instead for a “natural sweetener” like honey or agave nectar. Surely these all-natural forms of sugar are more healthful, right? Well, certainly not in terms of fructose content. Honey typically has about the same ratio as HFCS. Agave nectar can range from 56-92% fructose, depending on the brand. There are other options like evaporated cane juice, which vary in quantity of sucrose (and therefore fructose), but the best number I came up with was 85-95% sucrose, meaning 42.5-47.5% fructose.(5) The only mark I’ll give them above other sweeteners is that they’re less processed.

Now, I hear the murmurs in the audience, “so if fructose is bad and fructose is found mainly in fruits, does that mean we should avoid fruits?” Let’s look at the percentage of fructose in some common fruits, compared to equal portions of sucrose, honey, and HFCS-55.

Total Fructose Per 100g of Common Fruits (6)

FruitFructoseSucroseTotal FructoseTotal Sugars% Fructose
Apple7.63.39.313.370%
Grape7.60.07.618.142%
Strawberry2.51.03.05.851.8%
Mango2.99.97.914.853.4%
Papaya2.71.83.65.961%
Sucrose0.097.048.597.050%
Honey42.41.543.281.952.7%
HFCS-5542.40.042.477.055.1%

Uh oh…look at those apples and papayas. They have a high percentage of fructose, higher even than honey, sugar, and HFCS-55. Does that mean they’re bad? Not necessarily. Look at the total amount of sugar per 100g, then couple that with some fiber, vitamins, minerals, and other goodies that you don’t get in the sweeteners, contributing bulk that limits how much you can eat. So let’s not get twisted over fructose and think that means fruit is bad. I will say, unequivocally, that fruit is good. Some people need to watch the quantity because of the sugar content, but it’s unlikely you’re going to get fatty liver from apples (the highest fructose fruit I found).

So in an effort to wrap this up before hitting 10,000 words, let’s conclude. I have stated something similar in my previous post on PCC Natural Markets in Seattle banning products with HFCS and a discussion of sugar subsidies. High-fructose corn syrup is a scapegoat. It’s a scary name to throw out in a news report and banning it gets some of us health freaks all giddy. But let’s get real and deal with the facts. “High-fructose” is a modifier for the words “corn syrup” meaning that HFCS has more fructose, and hence more sweetness, than regular corn syrup. It is not a comparative term to other sweeteners. All of the sweeteners available in the store are just as high in fructose, as you can see above.

Don’t assume that a cookie or soft drink made with raw sugar or agave nectar or something else “natural” is healthful. Organic junk is still junk. I don’t care if it’s a cookie made with USDA-certified organic evaporated cane juice plowed under a Fair Trade banner. Your body doesn’t care either. Sugar is sugar once it hits the stomach acid and bloodstream. Just because it’s sold at Whole Foods does not make it good for you.

So what’s the best sugar you can eat? None. If you need (and I use that term loosely) to add something to your food or drink, use the least processed that you can get, which would be either honey or probably evaporated cane juice, and use sparingly. In the end though, avoid sweeteners as much as possible and stick to the natural sweetness of blueberries, apples, and papaya. We can argue until we’re blue in the face about what fruits are best due to lower fructose content and all of that, but if I can get someone to drop the cakes, sodas, and cookies, I bet they can eat apples all day long and be just fine.

One thing of interest that I found is that sperm cells use fructose as their primary fuel source.(3) It makes me wonder what the evolutionary reason for that could be. As I understand it, conception would have typically been desired in the late summer and fall so that the baby would be born in the spring when food was becoming more abundant. In the late summer and fall, plenty of fruits are available, with their higher fructose content than vegetables. I wonder if evolution worked in such a way that the sperm cells become most active from the available fructose at precisely the time when the pregnancy is desired. I may be completely out in left field with that hypothesis (not even sure that’s to the level of hypothesis), but it just struck me as interesting.

Sources:
(1) Monosaccharide
(2) Disaccharide
(3) Fructose
(4) High-fructose Corn Syrup
(5) Guide to Natural Sweeteners
(6) Table of Fruits and Sugars


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Tags: agave nectar, apple, blueberry, fruit, high fructose corn syrup, honey, soft drink, strawberry,Sugar and Fake Foods