[atrox (OP)]

Hi there,

I began this year with a good intention and started to drink a home-made smoothie every morning. I have to admit that I did not inform myself about smoothies before but just followed a gut feeling and actually also just liked those drinks (now I know that I should have been more critical, there actually seems to be some critisism around).
Well, it went in another direction than expected, as after some weeks I suddenly develop some digestive problems. After excluding infectional or organic reasons and reduced symptoms after stopping to drink those smoothies it turned out that I had developed a fructose malabsorption.
I now wonder what physiological processes are behind that sudden intolerance. Granted, I was never much of a fruits eating person (more veggies), but every now and then I ate fruits even in large amounts without any problems. Recently (about 3-4 weeks after my symptoms had disappeared) I ate pancakes with applesauce, something I never had any problems with and so I actually did not even give it a second thought. But after an hour or so I started to feel really bad and it was only then, when I considered the apple sauce... so I would deem a nocebo-effect as unlikely here. There seems to be a real physiological effect.

So what happend in my guts when I started to feed it fruits in the form of smoothies regularly? I read that there is a special protein that has to be there to absorb fructose. Has it been there before but now somehow it is not? How would that work? Is the production site destroyed, maybe due to an inflammation? Could you train your body to produce it again?

Thanks for your thoughts
Aj

[atrox (OP)]

Hi exothermic,

thank you for your reply, but it does not really answer my question.
Fructose transporter saturation does explain an acute intolerance of course but not really how I suddenly seem to be intolerant against foods I usually had no issue with. Even after going back to the regular diet I used to eat before (which basically means no fruits in any form, I also do not drink juices) and not having symptoms for 2 weeks I was not able to digest the apple sauce that had never been a problem before. So something changed obviously and I just wondered what it is and why and if ut could reverse back if I give the system some time to relax again.
I guess it has something to do with exposing a system that is not really used to fruits and regular high doses of fructose to a daily dose of smoothies. The system before was able to deal with irregular contact with (in some cases even high acute doses of) fruits. Now it seems my system has been overwhelmed with this after some time and is not able to deal with fruits at all anymore. I just wonder why.

all the best
Aj

[evan_au]

Could it be due to a change in your microbiome?
Maybe some bug really thrives on a steady supply of fructose, and now throws a party every time you eat large quantities of it?

[atrox (OP)]

Could it be due to a change in your microbiome?
Maybe some bug really thrives on a steady supply of fructose, and now throws a party every time you eat large quantities of it?

In this case it should be possible to "starve" them out again in trying to avoid fructose for some time completely. But I guess some weird bacteria in high doses would have been found in my samples.

@exothermic
The smoothies were the only thing that changed, so at least compared to my personal baseline I can quite good estimate how much more fructose I got there. So a smoothie for example was compiled of half a banana, half a mango, some spinach and joghurt. So that would add up to about 6g of fructose I ingested without it beeing predigested in the mouth so much before.
So while I know now, that my body is obviously not able to deal with this on a regular basis, I still do not know what happend there to also make me now unable to deal with those irregular doses after the regular doses long ceased to happen.

I now tried to read up a bit on this myself now and I found some answers to my questions.
Appearently GLUT5 expression is not fixed but is fitted to currend situations (consumption levels, age, time of day) and follows even a circadian rhythm. I kind of had the wrong idea that this would be a quite fixed trait in ones structure of the gut - so either you have thos proteins or not.
I read in a review study, that inflammation of the gut can indeed lead to a decreased GLUT5 expression. How this would work is not known yet and so my questions can not really be answered yet.
But appearently if I want to try one day again what I can digest and waht not a good idea is to start this in the afternoon due to the circadian rhythm of the protein expression.

There seem to be very many unknowns still. There are different hypotheses about what exactly causes a malabsorbtion in fructose. Either the GLUT5 transporters are not working propperly or there are just to few. Maybe the exchange of signals that trigger the expression of mRNA and subsequently the production of GLUT-proteins is disordered. Or maybe it is something else. Maybe a combination of causes. People seem to work on this question but do not have a conclusive answer yet.

So thank you for trying to help, I found now what I was looking for.

[atrox (OP)]

Excuse my ignorance, but as much as I appreachiate that you took the time to google this topic, I find your answers here a bit weird. I do not find your unreferenced full citations out of random papers (no worries, was no problem at all to find this paper you cited: "Diet and Inflammatory Bowel Disease" by Knight-Sepulveda et al.) or homepages very usefull, as my question was not tell me anything you know or you are able to google about fructose malabsorbtion, but was rather specific actually. Back in school it would have been a "failed - missed the point".

[chris]

It sounds to me like you have given yourself a "dysbiosis"; essentially, the profile of microbes that inhabit the intestine is a product of our daily diet. Different foodstuffs select for different microbial populations, so the bowel flora shifts and adapts to the diet. It's almost certain that part of what we call "traveller's diarrhoea" is a rearrangement of your microbiome in response to the challenge of a novel diet.

If a person radically and abruptly changes what they are eating, the microbial spectrum shifts; the bacterial equivalent of a domino effect then ensues, with different bug profiles triggering changes in other bug populations; the changes slowly ripple through the populations and reset the "shape" of your microbiome.

If you then revert your diet, the microbiome does not instantly switch back to how it was before. It takes months to re-adapt. This is evidenced by people who "yo-yo" diet; it may take 6 months for the microbiome to switch from a pro-obesity profile to a lean profile.

The next episode of the Naked Scientists will be looking at some of these questions. We'll publish the link to the podcast as soon as it is out.

[exothermic]

Excuse my ignorance, but as much as I appreachiate that you took the time to google this topic, I find your answers here a bit weird. I do not find your unreferenced full citations out of random papers (no worries, was no problem at all to find this paper you cited: "Diet and Inflammatory Bowel Disease" by Knight-Sepulveda et al.) or homepages very usefull, as my question was not tell me anything you know or you are able to google about fructose malabsorbtion, but was rather specific actually. Back in school it would have been a "failed - missed the point".

Speaking of ignorance & failure.... you asked 5 questions within your first post, yet you speak of specificity. Nonetheless, I answered your opening question directly i.e. "So what happend in my guts when I started to feed it fruits in the form of smoothies regularly?"

GLUT5 transporter saturation. You exceeded the carrier capacity of the GLUT5 transporter - thus altering it's expression.

What other questions would you like addressed?

[exothermic]

There seem to be very many unknowns still. There are different hypotheses about what exactly causes a malabsorbtion in fructose. Either the GLUT5 transporters are not working propperly or there are just to few. Maybe the exchange of signals that trigger the expression of mRNA and subsequently the production of GLUT-proteins is disordered. Or maybe it is something else. Maybe a combination of causes. People seem to work on this question but do not have a conclusive answer yet.

Sounds like you need to do more research.

Rab11a are GTPases which are key regulators of intracellular membrane trafficking. The literature suggests there is a dysfunction in Rab11a dynamics following GLUT5 transporter saturation - this downregulation of Rab11a recycling in intestinal epithelia alters GLUT5 trafficking to the apical membrane, which reduces mRNA expression of GLUT5 as well as it's baseline activity.

Any questions?

~