Fructose. We have all heard of this simple sugar. It's in just about every processed food in the form of high fructose corn syrup. It is also in some “health foods” in the form of agave syrup, honey and maple syrup. Fructose is also found in fruit (and a small amount in vegetables). If we get our nutrition information from television commercials, we are told HFCS is bad, no, wait, sugar is sugar, it's not bad, apple juice is part of every kids healthy diet and we all should eat more fruit and vegetables. To really understand the dangers of fructose, we need to understand what sugar is made of, where it hides, and how the body metabolizes it.
Is sugar just sugar?
When we think of sugar, we think of the 5 lb. bag of white granules in our cupboards, used for baking cookies and cake. This sugar is SUCROSE, a disaccharide (meaning two), made up of two sugar molecules, GLUCOSE and FRUCTOSE. Uh, oh, good old white sugar has fructose too. In fact, it is 50% fructose and 50% glucose. Glucose and fructose are monosaccharides (meaning one), they are what they are. There are two other disaccharides, LACTOSE (glucose + GALACTOSE) which is milk sugar and MALTOSE (glucose + glucose) which is malt sugar. Confusing, I know, for those of us that are visual learners, refer to the table below.
How many different kinds of sugar are there?
If we read the nutrition label on foods that contain sugar, in addition to sucrose, fructose, lactose, maltose, and glucose, we will see it disguised as: high fructose corn syrup, honey, agave nectar, maple syrup, fruit juice concentrate, cane sugar, beet sugar, coconut sugar, corn syrup, corn sweetener, cane juice, evaporated cane juice, malt syrup, brown rice syrup, brown sugar, powdered sugar, carob powder, maltodextrin, dextrose, (this list continues to grow as food manufacturers try to trick us more and more). Each of these different disguised sugars is made up of sugar molecule(s). The bottom line, SUGAR hides everywhere.
How does the body metabolize sugar?
Almost all carbohydrates (grains, fruits, vegetables, beans, rice, pasta, processed foods, etc.), are broken down or metabolized into glucose in the body. We call this circulating glucose, blood sugar. When blood sugar increases, insulin is released to direct traffic, so to speak. This circulating blood sugar can be used for immediate energy, stored as energy in our muscles or liver for later use, or converted to fat and stored in our fat cells. When this well orchestrated process goes awry, which it does for about 75% of the population, we not only get fat, but we end up with disease as well.
The exception to this process is our sugary friend fructose. Fructose is a simple sugar that does not get metabolized into glucose. It is, what it is. Fructose is not a friend of insulin and instead of swimming in our blood stream, it goes right from the small intestine into our liver. The liver then does it job, by metabolizing fructose into liver glycogen and storing it for later use. If our storage tank for liver glycogen is already full, fructose is turned into triglycerides, LDL cholesterol and uric acid. This spells out bad news: coronary heart disease, heart attack, stroke, gout, kidney stones, non-alcoholic fatty liver, metabolic syndrome, obesity, no thanks! An interesting side note, fructose was sold as a diabetic friendly sugar because it did not elevate blood sugar. Now, you know why.
Is all fructose the same?
All fructose is metabolized by the liver. No exceptions. So whether it comes from fruit or candy, the metabolic process is still the same. Where we get into trouble with our consumption of fructose is when our little liver glycogen tank is already full. The liver can hold roughly 70-100 grams of glycogen, however, fructose has to share this tank with blood glucose as well. On a typical American diet, liver glycogen stores are almost always full, with the exception of first thing in the morning. This is because, our body uses about 15g of liver glycogen during an overnight fast (15g of fructose is about the equivalent of 6 oz. of grapes). With our liver tank almost always full, all the incoming fructose is turned into fat.
I thought fruit was good for us?
Fruit's redeeming quality is it is full of antioxidants that fight free-radicals, which cause aging. A few small pieces of fruit (not a glass of fruit juice) a day, is not going to put us over the fructose budget as long we are eating a diet rich in real food; proteins, fats, non-starchy vegetables, maybe a sweet potato or two, nuts & seeds. However, what we know, is the standard American diet is far from this. Although it is entirely possible to eat too much fruit (especially if we are eating dried fruit), we aren't on fructose overload from overdosing on fruit, no, it's the astronomical amount of processed food and drinks that are consumed daily.
And the bottom line is?
It is no secret the amount of sugar Americans consume. The amount is enormous and it keeps rising. Sugar, in its many forms, natural or processed, is not good for us. Although the amount of fructose we consume should be limited, especially from processed foods and drinks, so should the amount of sugar and carbohydrates in general.