Upon hearing „fruit sugar“, most of us think of fresh, sweet fruits. This isn’t wrong in general, but fruit sugar or „fructose“ is much more than that. In this article I’ll try to explaint what fructose is exactly, where you can find it and how it is related to fructose intolerance.
Before I do, let me emphasize that I am neither a doctor nor a nutrition expert. Everything you can find on here are my own experiences as someone affected and my findings in books and the internet.
What is Fructose?
This one is easy to answer. Fructose, or fruit sugar as the name implies is a sugar and thus a carbohydrate. What’s special about fructose is that it’s a monosaccharid, meaning that (together with glucose and maltose) it’s the smallest sugar to be found in nature.
Where do we find Fructose?
In nature, fructose is found in every crop. Therefore it’s not only found in fruits, but also in vegetables and grains. What differs is the amount of fruit sugar found. Fruits such as apples and pineapples for example contain a high amount of fructose while grains only contain a little.
Outside of nature, monosaccharides are also found as part of oligosaccharides and industirally processed food.
To help you visualize, here’s a small list of foods that contain a high to very high amount of fructose:
Sugars: sugar, invert sugar, cane sugar, coconut sugar, birch sugar
Sirups: agave syrup, maple syrup, honey, sugar beet molasses, isoglucose, fructose-glucose syrup
Bulk sweeteners: sorbit, isomalt
All of these are often mixed into procuts like yoghurt, drinks, sausages and instand foods to sweeten their taste or make them more durable.
How does our body process fructose and how is it related to fructose intolerance?
Especially when talking about fructose intolerance, it’s important to know how a healthy body processes the fructose contained in our food.
Let’s say a healthy human eats an apple. This apple is thoroughly chewed and passes through the esophagus to the stomach. Within your mouth and stomach the apple is split into its parts. Enzymes make sure that every carbohydrate consumed is split into a monosaccharide. These monosaccharides then pass your duodendum to reach your intestines .
There the nutrients such as our monosacharides are passed through the intestinal wall into our blood stream. Some nutrients such as glucose can pass the intestinal wall without further help (a process called „active transportation“). Fructose is not one of those and instead requires an enzyme called „Glut-5“ to pass. If enough Glut-5 is present, the fructose passes into your blood stream entirely and form there on can be used as energy by your body.
This is where fructose intolerance sets in. People who weren’t born fructose intolerant (a condition called fructose maladsorption) do not have enough Glut-5 to process more than a certain amount of fructose. Thus, not all of the fructose consumed can pass the intestinal wall and continues on into the lower intestine, together with the rest of the unprocessed chyme.This is where fructose (or sugar in general) becomes a problem.
There are lots of bacteria in your lower intestine who further process everything that passes through. These bacteria process sugar into fatty acids and gases which in turn cause the symptoms of fructose intolerance.
What are the symptoms of fructose intolerance?
Experiencing symptoms is how most people come into contact with their intolerance. It starts with not feeling well after a meal. You experience stomach pains and diarrhea and sometimes lesser symptoms like headaches. Here’s a small list of symptoms I usually experience/know of:
diarrhea / constipation
headaches (up to experiencing migrane)
How do you diagnose fructose intoleranz?
Fructose intolerance can be diagnosed in two ways: You either do an exclusive diet or you get tested by a doctor of your choice.
“Exclusive diet“ means that for a set amount of time (usually two to three weeks) you keep a very strict diet. In case of a fructose intolerance, this means not eating any fructose at all. If your symptoms get better or disappear entirely over time, you probably are fructose intolerant.
The best way to be sure is to consult an allergologist though. I also consulted a professional and had myself tested. The test consists of drinking a larger amount of fructose, dissolved in liquid. This mixture has to be consumed on a sober stomach over a short amount of time. Now there are two ways agein to diagnose fructose intolerance: Either you regularily have your blood tested over time for a rise in fructose levels or you can have your breath tested. Both ways are very precise and allow for a diagnosis.
A diagnised fructose intolerance – what to do now?
When I got my diagnosis, I already knew what it would be. Shortly after doing the test, I experienced symptoms so heavy that I didn’t have to wait for the test results. The first bathroom break I had to have after already confirmed my suspicion. The only thing I got from my doctor after receiving the diagnosis was a short list of foods I was supposed to avoid from now on. Everything else I had to find out on my own. It’s hard to know what to do, but after some research online and buying some books on the matter I knew how to go on.
It is recommended to have a two week elimination period after your diagnosis. In this period you try to not consume any fructose at all – or at least keep the consumed amount at a minimum. Unless you’re exclusively eating at home this can be rather hard, but using nutritional tables and planning your meals can help a lot.
After two weeks, your symptoms should have gotten better and your intestine should’ve calmed down. If this is not the case, it’s recommendable to prolong your elimination period. I for example had to keep a four week elimination period since my body took a little longer to calm down. I also recommend consulting a doctor again if your symptoms haven’t gotten better withing two weeks, since it’s possible that other illnesses, intolerances or allergies could play into your condition as well. If ignored these may cause additional ill side effects and sicknesses.
After the elimination period, you can start the next phase.
It is very important to test out your very own personal limit for fructose consumption. My tool of choice would be to keep a nutrition diary. In this diary, you keep track of what you ate, how much fructose it contained and how your body reacted. Weighing your food and keeping track of every bite can be kinda hard and annoying in the beginning, but keep in mind that you’ll get accustomed to it you won’t have to do it forever.
To find out your upper limit, slowly raise the amount of fructose you consume in your everyday food. In the beginning you can add fruits that only contain a low amount of fructose to do so. I recommend using only a single fruit or vegetable of your choice, because this makes it easier to filter foods that may contain low amounts of fructose but still cause symptoms. Once you’ve found your limit, it is heavily recommended to eat at your limit everyday.
Even though fructose intolerance may look like some kind of insuperable obstacle, in the beginning and you can already see your self eating bread and water for the rest of your life, it’s not as hard as it seems.
The biggest downside probably is gonna be being abstintent of cake, ice and sweets, but on this blog I’ll try to offer you recipes you can use to create your own delicacys. Another large downside is the abstinence from most fruits. That one was (and still is) especially hard for me. But no fruit in the world is worth constant stomach pains and other problems.
On the bright side though, this condition forces you to keep an eye on your diet and thus to do good for your body and soul.