So last week I did the Fructose challenge as part of the lowFODMAP Challenge Phase. And I was very surprised to discover I don’t tolerate fructose so well!
With just a small portion (4 sun-dried tomatoes) I started getting cramps, although relatively mild, only two hours later. The next day I had a medium size portion and it was horrible!
But I shouldn’t have been so surprised:
Around 45% of people with IBS will have some degree for intolerance to fructose!
So seeing as fructose is something a lot people watching this are going to have to limit, I thought I’d share some more information about it and what you need to avoid.
What is Fructose?
Fructose is a single sugar molecule. It’s either found on it’s own (free-fructose) or paired with glucose (glucose + fructose = sucrose) or as a long-chain of fructose molecules all strung together, which is called a fructan (which is a FODMAP!).
Free fructose is usually absorbed directly into the bloodstream during digestion in the small intestine.
Now it’s worth explaining that sugars don’t just move through the wall of your intestine on their own. Your body likes to keep control of the movement!
So free-fructose can moved into the blood via a special transporter or “selective door” in the cells’ walls called GLUT-5. But GLUT-5 isn’t very good and can’t let very much in at once.
Luckily there is a second door the free-fructose can take called GLUT-2. However there is a catch with this door. The fructose needs a glucose partner to get in. Like needing a date for a party, or it’s no entry.
This means that if there is a lot more fructose than glucose, a lot of the poor lonely fructose’s will be left out in the cold. They’ll be moved along to the colon where bacteria will start to rapidly ferment them into hydrogen, carbon dioxide and short-chain fatty acids. Which leads to all those lovely IBS symptoms!
There is also a condition called Hereditary Fructose Intolerance, which is very different. If you have this, if means your liver is lacking a certain enzyme needed to metabolize the fructose once you’ve absorbed it from your food.
High-Fructose Foods to Limit or Avoid
Apples (apart from a small amount of granny smith if you’re okay with polyols)
Guava if it’s unripe, but you can have a whole one if it’s ripe!
Pears (apart form prickly pears, which are completely different and lowFODMAP)
Sweeteners & Syrups
Agave or nectar syrups
High-fructose corn syrup
Sugar snap peas
Lotus root, dried
Sun-dried tomatoes, more than 2
Artichoke, more than half a heart
I’ve been using the Monash Uni FODMAP app, which has a filter option to highlight high fructose foods. Very handy to learn this new category of things to avoid.
TOP TIP: Exercise immediately after consumption can exacerbate the symptoms by decreasing transit time in the small intestine, resulting in a greater amount of fructose emptied into the large intestine.
So whatever you do, don’t eat a mango straight before a Zumba class!