Sugar! (da da da da da da) by Roger Pink

Sugar!

When you hear the term sugar, the first thing that probably comes to mind is granulated table sugar, along with maybe sugar cubes, brown sugar, or the powdered sugar you get on a jelly donut (Ok, that last one may only be me). In fact, all of those things I just mentioned are just one kind of sugar, called sucrose. Other types of sugars that you've probably heard of are glucose, dextrose, fructose, and lactose. Some sugars you may or may not have ever heard of are galactose or maltose. Everyday we consume a multitude of sugars in many different forms without a second thought. That ends today! Today we cover part one of my one part series, "Better Know a Sugar." Let's become sugar experts!

What is Sugar?

There are basically four types of carbohydrates. They are monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Chemically, a saccharide is a ring of four or five carbon atoms and one oxygen atom. The term sugar generally refers to the first two types, which are made up of one (mono) saccharide* or two (di) saccharides respectively. Oligosaccharides and polysaccharides are longer chains of saccharides, sometimes referred to as complex carbohydrates, and are not relevant to this discussion.

The Monosaccharides

Monosaccharides include fructose, glucose, and galactose and are referred to as simple sugars. Although at left you can see they have slightly different chemical structures, they all have the same molecular formula, C₆H₁₂O₆. Glucose and galactose are epimers, whereas fructose and glucose are isomers (as are fructose and galactose).

Of the three, only glucose is ready to be used or stored by the body immediately. Fructose and galactose must be phosphorylated in the liver by fructokinase and galactokinase respectively.

Fructose is the sweetest of the three monosaccharides (as can be seen on the right), more than twice as sweet as glucose, and almost six times sweeter than galactose. As you can see, no other sugar tops fructose for sweetness. The disaccharide sugars are just two monosaccharides chemically combined, so they tend to be less sweet overall because the sweetness of their parts average out.

It is interesting that we have evolved to perceive sweetness as we have, since our perception of sweetness certainly has such a huge effect on our diet. If you are curious about how humans (mammals in general) detect sweetness, you can check out this explanation.

The Disaccharides

There are three disaccharides, which consist of combinations of the monosaccharides listed above. There is Lactose, which is a combination of a glucose and galactose and is found in milk. There is maltose, which is a combination of two glucoses and is found in germinating seeds like barley. Finally there is sucrose, a combination of fructose and glucose and found in most vegetables and fruits, as well as maple syrup, granulated sugar, etc.

Sucrose is the most common of the disaccharides. When we say sugar, we usually mean sucrose. Fruits and vegetables tend to have some combination of the monosaccharides, fructose and glucose, and the disaccharide sucrose in them. The quantities and the ratios of the respective sugars determine the sweetness of the fruit or vegetable. For instance, an Apple, on average, has 10.4 g of sugar per 100 g. Those sugars are 5.9 g fructose, 2.4 g glucose, and 2.1 g sucrose. A sweet red pepper has 4.2 g of sugar per 100 g and those sugars are 2.3 g fructose, 1.9 g glucose, and 0.0 g sucrose.

Here are some other common ratios. I'm using the notation (F,G,S) to mean (percent fructose, percent glucose, percent sucrose). Cantaloupe (24F,20G,56S); Apricot (10F,26G,64S); Pineapple (21F,18G,61S); Banana (40F,41G,19S); Grapes (48F,45G,7S); Papaya (48F,52G,0S).

As I mentioned earlier, granulated sugar is all sucrose (100%). Maple syrup is 95% sucrose. Honey, which has been used as a sweetener for thousands of years, is only 1% sucrose (50% fructose and 44% glucose and 5% other sugars). The most common kinds of high fructose corn syrup, HFCS-55 (55% fructose/41% glucose/4% other) and HFCS-42 (42% fructose/53% glucose/5% other) both contain no sucrose.

If you notice, high fructose corn syrup (HFCS) is pretty close to honey in it's sugar ratios. Basically the west has gone from sweetening with honey (fructose/glucose) for millenia, to sweetening with granulated sugar (sucrose) for centuries to sweetening with HFCS (fructose/glucose) for the past few decades. Any dietary criticism that is applied to HFCS pretty much applies to honey as well, as they are almost identical to each other in their sugar makeup.

Sugar Consumption and HFCS Controversy

As you can see from the graph on the right, U.S. sugar consumption per capita is actually going down and our consumption of HFCS is leveling off. Sucrose, so dominant up until about 50 years ago, has lost a lot of ground to HFCS as a sweetener due to tariffs on imported sugar and subsidies for growing corn, but the trend seems to be changing, probably due to HFCS health concerns.

There has recently been a lot of concern raised regarding the healthiness of HFCS. Mostly this is due to the differences in how fructose and glucose are digested (fructose tends to produce more triglycerides). It is important to remember though that sucrose is really just bonded fructose and glucose. It's true the body must break apart the sucrose through hydrolysis, but after it does, you simply have fructose and glucose, much as you do when you consume HFCS. The ratios of fructose to glucose from sucrose as compared to HFCS are slightly different, but not by very much (the ratio of fructose and glucose from digested sucrose is 50-50 as compared to 55-41 for HFCS-55).

Conclusions (And Thanks)

So that's where we are at this moment with sugar. You'll notice that whether it was honey in ancient times, granulated sugar the past few centuries, or HFCS today, it's all basically the same stuff. A combination of fructose and glucose, roughly around a 50-50 ratio. That shouldn't be surprising considering the millions of years of evolution that got us to this point. Vegetables and Fruits are a major component of our diets and the more sugars in those fruits, the better our chance of survival (sugar=energy). It only seems natural that we should find such foods so pleasurable to eat and we should prefer our sweeteners to have similar fructose/glucose ratios. The problem is, what was once a benefit to us in prehistoric times can now be problematic in our lower calorie burning, higher calorie consuming modern world. Sugars are just too efficiently digested and stored by our bodies for us to over consume them as we do, but that is for another post.

Getting back to sugar, I hope I was able to shed some light on this common yet sometimes mysterious food. I certainly know I was surprised in my research for this blog entry how similar the chemical structures of different sugars are. And how small chemical structure changes, say between glucose and galactose, can result in such a large difference in both perceived sweetness and function.

I also wanted to take a moment to say thanks to everyone who has been reading my blog entries the past few weeks. I appreciate you all taking time out of your days to see what I've posted. I hope you all will continue to come back, learn new things, and leave feedback.

Best Regards,
Roger