Does Fructose Make You Fat?

appleshaped body comic_COLOR

Have you ever seen the commercial sponsored by the Corn Refiners Association claiming that there is nothing wrong with high fructose corn syrup? That it’s “just sugar” and your body can’t tell the difference? If you haven’t, check it out below. I laughed out loud the first time I saw it air during prime time television. Unfortunately, this is the type of media messaging that is accessed and absorbed by American viewers, particularly adolescents and mothers. It is strategic and smart marketing on their behalf, because the next time these consumers are at the grocery store and happen to glance at the ingredients on a product, they’ll most likely remember, “Oh yeah, high fructose corn syrup isn’t even bad for you. It’s just sugar.” How terribly wrong.



There has been a lot of back and forth between fructose being bad and good for you. Personally, I try not to villainize any food group, macro or micronutrient. But, I recently gained some insight into how fructose is metabolized in the body in my biochemistry of nutrition class. When I say fructose, I don’t want you to think I’m referring to a piece of fruit here and there, a breakfast smoothie, or having a plethora of seasonal watermelon in the summer. This is naturally occurring fructose and these levels can be handled by metabolic pathways in healthy individuals. Rather, I’m talking about the American population loading up on sugar-laden candies, sodas, breakfast cereals, and many processed foods that contain high fructose corn syrup. THIS is when you run into trouble. Quite frankly, this is the reason why our country’s obesity rate is rising by the day.


In this commercial, the mom wandering around in a corn maze (??) is basically saying that sugar is sugar – it doesn’t matter what form it’s in – the body recognizes it all as the same thing. Well, this is loosely true. It’s sort of like saying a Ferrari is the same thing as a Chrysler Sebring; both can be convertibles, have four wheels, and get you from point A to point B. See my point? This lady/actress and Michael Scott are most likely good friends.


So, what’s false about this commercial??

Well, there are many different types of sugar that exist. Let’s start out with the basics and then I will show you how high fructose corn syrup is linked to them. Glucose is our body’s (and brain’s!) main, most easily metabolized, and preferred carbohydrate fuel source. It is a monosaccharide, which is the most basic sugar/carbohydrate form that exists. As such, glucose can be metabolized by any cell in the body. The other monosaccharides are fructose and galactose. Glucose, fructose, and galactose all have a chemical formula of C6H12O6, which is about as far as their similarities go. The difference lies in the placement of the carbon, hydrogen, and oxygen bonds in their structures, as can be seen in the diagram below. Your body is picky, it knows the difference between these sugars very well, contrary to what the corn refiners say:


carbon structure

Now, one of the main reasons we ingest glucose, or any food for that matter, is to break it down in order to utilize its caloric energy or store it for later on. In chemistry terms, “energy” is basically referred to as ATP, or adenosine triphosphate. Ring any bells??


So, you have a nice bowl of pasta for dinner. What happens? Glucose is released from the carbohydrates, it raises your blood sugar, your brain registers this, and insulin is secreted to get the glucose out of the bloodstream and into the cells where it can be burned, in this scenario. Once in the cells, it enters glycolysis, which ends in the formation of pyruvate. Pyruvate makes its way to the Krebs cycle, and eventually yields a total of 36 ATP – aka energy for your body to use as it sees fit. This mechanism is highly complex and works extremely efficiently since regulating blood sugar is integral to our homeostasis.


Why, then, would our body have two separate pathways to breakdown fructose and galactose if the one I just discussed for glucose works so well? It doesn’t.

Fructose and galactose undergo short reactions to rearrange their structures in order for them to enter glycolysis just like glucose. This saves the body a lot of energy. One of the ways fructose undergoes this type of rearranging can be seen in the below diagram. When fructose enters the liver, it requires a bit of effort to get it into glycolysis, into which glucose would normally slip so easily. (Warning – I have no graphic design talent):


fructose metabolism diagram 2


As you can see, fructose eventually needs to be converted to glyceraldehyde-3-phosphate. This is accomplished by adding a phosphate. Where does this phosphate come from? The P in ATP!


Translation: It costs your body energy every time you ingest a molecule of fructose.

Now, the sugar we ingest – what form is it in? Cane sugar, also known as table sugar or sucrose, is 50% glucose and 50% fructose. Not that bad. This is also naturally occurring. High fructose corn syrup, on the other hand, is a man-made sweetener and preservative that has chemically altered the glucose in corn starch to become fructose, resulting in a super sweet and palatable end product. Is corn a fruit? Not the last time I checked. Hmm … Anyway, as a result, HFCS is 55% fructose and 45% glucose. In your body, this translates to a lot more fructose that needs to be broken down.


Unlike glucose, which can be processed in all cells of the body, fructose can only be metabolized in the liver. In a previous post, I emphasized how overburdened the liver is on a daily basis with its metabolic duties. So, if you are inundating your body with fructose on top of everything else, you will really be depleting the liver of its energy stores. If you and your liver are energy deficient (which is very common), the glyceraldehyde seen in the diagram will stand alone, phosphate-less, and be unable to enter glycolysis.


Where does this leftover glyceraldehyde go? It stores itself in the adipose, or fat tissue … You gain weight.

 heavy bird in tree

What is also interesting is when you ingest glucose, it provides a “satiety” signal to the brain. This signal assists insulin in getting the glucose out of your blood and into the cells. Fructose, on the other hand, is not used by the brain for fuel. Therefore, it never gets there to provide that same message of, “I ate, that was delicious, I’m satisfied, you can put down the fork now.” Moreover, the transporter that pushes fructose out of the blood and into the cells is not insulin dependent. Consequently, your tissues can’t really absorb and process the fructose as readily. Once the fructose is able to get in the cell, if in excess, it will react to form components of triglycerides more readily than glucose would. Sorry to break it to you, but there’s always excess fructose floating around when you’re consuming high fructose corn syrup. Which means, you’ll usually be forming triglycerides, which are fat stores.


In addition to not stimulating insulin, fructose fails to stimulate leptin hormone production. Leptin is the key hormone that regulates your hunger signals. If it’s not working, you will always feel hungry, never feel satisfied, and your body will hold onto the weight because your brain is telling it that you haven’t really eaten, so why burn it? Our bodies are very smart and protective of our survival. So, you can see how a diet high in fructose over a long period of time can throw off your sugar metabolism and appetite, right? This is a recipe for consistent weight gain and insulin resistance –> diabetes –> obesity!


So, yeah, I would have to disagree with that commercial. Shame on them.


Peace of mind starts on your plate – or in the produce section, in this case. Not in a Pepsi can.

If there’s one thing you can remove from your diet as a first step toward breaking that ceiling, slimming your waistline, and lowering your risk for diabetes and obesity – get rid of the high fructose corn syrup.


Happy Holidays!!



Research cited: Ferder, L.; Ferder, M.D.; Inserra, F. The Role of High Fructose Corn Syrup in Metabolic Syndrome and Hypertension. Current Hypertension Reports, 2010, 12, 105-112.



  1. Benjaminsays:

    I loved it! Another great post. I thought the commercial was hilarious in a way that I can’t believe it is allowed on the air. I also appreciate the detail of the post – it’s nice to know what actually happens in our bodies when we eat sugar. Happy Holidays!

  2. Denisesays:

    Great information for everyone to learn to get and stay healthy. Good job Erin.

Leave a comment

Please be polite. We appreciate that. Your email address will not be published and required fields are marked