A about 2 years ago (after feeling poorly for about 18months), I was diagnosed with Fructose Malabsorption. Once I tuned my diet accordingly, by figuring out what amount of fructose I could tolerate, the change was amazing (back to feeling good, having energy again, and no mood-swings!).

As someone with FM, I can offer the following resources that I've found helpful over the years:

• Good intro on FM: http://sites.google.com/site/fructmal/diet
• List of foods that you can eat or should avoid: http://www.thefartingpear.com
• The Definitive FM test: Ask your Dr to book you for a hydrogen breath test, where they give fructose before hand.
• The experts: Sue Shepherd has done the most research and testing on FM. Read anything you can get your hands on from her.
• Help: There is a very active, very helpful yahoo group; "Fructose Malabsorption Australia": http://health.groups.yahoo.com/group/fructose_malabsorption_australia/

Also, since it has not been mentioned yet, I should also highlight that fructose and fructans (chains of fructose molecules) must be avoided. These are present in Wheat, brown rice, onions, green beans, carrots, asparagus, garlic, and some other stuff (see: http://www.thefartingpear.com/index.php/foodsearch/index/fructans).

My digestive system has been screwed up since I was a kid, so I think I have a predisposition for food intolerances. I have a ton of them (many of which are irrelevant with this WOE, thank goodness), fructose malabsorption included. I did a fructose elimination diet a while ago and found I don't tolerate it either. After I cut out all fruit and higher fructose veggies (for a couple months), I started gradually adding fructose-containing foods back in one by one and found I was supper sensitive. I had a reaction after any sort of fruit or higher sugar vegetable (like carrots) I tried.

I think most people can tolerate the small amounts of fructose in fruit. I think after a person clears their system of it, the reaction to fructose will be more pronounced from their perspective because they've gone thirty days without it. Once you realize how good you feel without something you can't tolerate, you notice it more when that something makes you feel terrible. Though I don't know if your tolerance of it actually lessens once you rid it of your system.

ETA: I know I said "tolerance" a lot in my response but fructose malabsorption is, as the name suggests, a malabsorption issue. It's not a tolerance issue.

Fructose Malabsorption Disorder is the inability to absorb fructose and fructans. This condition is NOT characterized by the inability to "tolerate" fructose/fructans. Sufferers of Fructose Malabsorption have no difficulty tolerating fructose/fructans once they have been absorbed. However, inducing absorption is difficult or impossible for FructMal sufferers. The symptoms of the disease are the result of having unabsorbed fructose/fructans in the lower intestine.

Link.

I would be cautious about interpreting a 30 day fructose elimination.

I do not know specific details, however many transporters like the GLUT5 that absorbs the fructose from the small intestine are regulated by the presence of the molecule they take up. What this could mean is that if you eat no fructose for a month your ability to absorb fructose could be greatly reduced. Reintroducing it could result in malabsorption and may take a day or two before you can produce new GLUT5 transporters. Thinking you have a malabsoption problem when you don't doesn't help anyone.

Also the absorption of fructose takes place near the tips of the villi of the cells of the small intestine. Any damage to the villi, such as from celiac disease or other gut disease, could reduce the ability to absorb fructose. Maybe any malabsorption problems would improve again with a healthy gut lining.

Fructose malabsoption seems like an interesting new idea and reducing fructose looks like it could be a usefull experiment if you have possible symptoms like IBS.

Seems possible if the fructose uptake mechanism in your intestine is deficient... I would say this seems rare (would be extremely evolutionary unfavorable). Just from personal experience I haven't heard many people complain of loose stool/ excessive gas from eating fruit (via increase of osmotic pressure in the intestines/ bacteria breaking down undigested fructose) If it were getting in your body since it is a simple sugar there is no enzyme which needs to break it down... only an enzyme in the liver which needs to convert it to pyruvate --> glycogen. So, like this website alludes to, I'm hesitant to believe it can be very similar to lactose intolerance. Of course I'm sure there are a handful of mutations in the aldolase which converts fructose into a glycolysis intermediate that decrease its affinity... but it seems that people who suffer from fructose problems typically do so because of a malabsorption issue. If you keep it down you should be fine (I think gluten's a lot worse)

I DO think that this is a very important step in an optimal diet. I just really love fruit... so I eat 10 blueberries and a teaspoon of honey after my workout. Its definitely not necessary and if you can live without it, more power to you. (just don't go crazy on the glucose) Raw fructose is about 1.7x sweeter than sucrose so you can eat a bit less of it for the same punch (heating catalyzes the reaction to a 6 carbon fructose sugar that is about the same as sucrose so it mitigates the advantage). I'm gonna stay with a bit of fructose / day, but if I could ever give up sugar. It would be a good day.

On the evolutionary side: We have specialized transportation systems for fructose (see Glut5 transporter), so I can't say I think it decreases our fitness too much (evolutionarily speaking... although optimal health/ your health goals may need a different analysis)

Large amounts of fructose are not easily digested, usually 50 gr being the maximum most people can comfortably handle.

The ratio between fructose and glucose in fruit is also important, as glucose helps with fructose absorption. If you look at the nutritional values, you can identify (and avoid) fruits that are high in fructose and low in glucose: apples, pears, melons (especially water melon) are among the worst offenders.

Other food intolerances (gluten) can cause fructose malabsorption but often, once you fix the first problem, fructose malabsorption disappears.

Final thought: are modern fruits too sweet for us to digest properly?

Sometimes if a population is away from a food source for a long time, and there is no natural selection towards a needed ability, then this ability can degrade or become lost. Just like fish in underground caverns eventually lose all their pigment and eyesight over the generations. Things are not conserved if they are not needed. It could be that some populations did not have access to much fructose and so their ability to process and tolerate it has degraded. However, since there is a specific metabolic pathway in the average human that is specifically set up to handle fructose, I do not think it likely that humans in generally were generally designed not to eat any at all. I do think were were designed to eat much much less than currently eat on the average SAD. And I also would not be surprised if people with all kinds of gut damage, blood sugar issues, and gut flora imbalances would have added problems with any kind of sugar or starch. However, I do think that for the big majority of humans, moderate intake of fructose such as would be obtained from moderate intake of whole fruits, if done from childhood such that metabolic damage never happened in the first place, would be perfectly fine. However, if I were native American, innuit, or one of the groups that might be less adapted to carb intake, I'd be extra careful.
-Eva

Thoughts on fructose malabsorption on Evolutionary Psychiatry:

http://evolutionarypsychiatry.blogspot.com/2010/08/ibs-fructose-depression-zinc-and-women.html

I am unable to eat most fruits as well. The only thing I allow myself is a little lime juice when I cook fish. I seem to do ok with that so far. It can be very limiting here on Paleo but possible. I just focus on meats and veggies, and I do use lactose free milk and butter. :) I have not tried to reintroduce other fruit and don't miss it. I never really liked it to start with. I do however wonder if this could be a reason I have low energy.

Fructose malabsorption is not a food allergy, meaning there is no production of IgE antibodies or release of histamine. There is also no typical allergic symptoms, like itching or hives.

fructose malabsorbtion is certainly real, and can run in the family (genetic). however, i found that the capacity to absorb fructose varies very widely depending on the health of my gut flora. for example, one could have a bacterial disbyosis or candida overgrowth in the small intestine and think that it's FMA. meaning: try to reset your colon (maybe 1-2 days fasting, eating only macadamias or so), populate it with the most effective probiotics (like L. GG ("culturelle"), boulardii, coagulans, etc) and it might very well be that you can tolerate much more F. than ever before (it might not cure the FMA, but at least it changes how the remaining F. is being metabolized afterwards in the colon)

So, Ive been living with my Fructosemalabsorption for a year now. I pretty much know what I can eat and what to stay away from. Id like to change my whole dietto paleo diet - of course eating only veg./fruits I can. Has anyone here made experience with it? If yes did you realize a better absorption of fructose? I heard that might happen....very curious bout that. Monika

This is a great question. I'm happy to report that even when I was very sick with (unrecognized) gluten sensitivity I was able to handle fruit just fine so the good news it doesn't happen to everyone. This site says it actually helps to eat glucose with your fructose.

I have gone 30 days or more without fruit and when I re-introduced it I felt much better. While some raw vegetables produce excess gas for me, etc., fruit does not.

I was shocked to hear the 50g per day max, though--other than my days of slugging HFCS Coke and Pepsi that's a lot. So despite all my PH defense of fruit and fructose I'm pretty much in awe of anyone who frequently eats 50g or more.

My typical daily intake (a grapefruit and a banana or handful of berries) plus about a tbsp of honey. My total sugars may approach 50g but my fructose is definitely less if you check the tables at the link I provided. Even when I get a pineapple once in a while I don't hit 50g of fructose that day thanks to portion control and skipping the other fruits.

fructose malabsorption is medically diagnosable with a hydrogen breath test. If youre concerned, see your doctor.