It took my 3 days on the Fructose malabsorption (FM) diet to be pain free and diarrhea free. But, to be honest the first time I tried the FM diet for 2 weeks it didn't work because I didn't eliminate enough foods. You may need to do some sort of food elimination diet at first.
Here are somethings that can make the FM diet fail:
1. Additional intolerance in addition to FM. I can't handle high amounts of flax seed and spinach.
2.Sometimes I think I need something in my system to ferment. If I go ultra low-carb I get instant pain free diarrhea. If I add enough vegetables in like broccoli, cauliflower, turnip greens I can go ultra-low carb with no problems.
3.Most of the time I think my body over ferments food. If I add in apples or my fructose load is too high for the day I end up with delayed diarrhea (diarrhea shows up 3 days later), severe pain and constant thirst. My fructose load can be too high if I eat too many carrots or sweet potatoes for the day. The longer I'm on the diet the less I worry about the fructose load, but in the beginning if I had too much fructose in my system it was a problem.
Even the smallest amount of onion can cause delayed diarrhea and pain. There is onion in most restaurant foods.
Sometimes lettuce has fructans in it; usually in the ends. 97% of the time lettuce is okay.
Sometimes people with FM have trouble with beneficial bacteria, fermented foods and vitamins. Unfortunately, you have to figure out some of this stuff on your own. I've found fermented buckwheat and any type of cheese, including cottage to be the safest fermented foods. Everybody has a different system. Some people can get diarrhea from too much magnesium or vitamin C.
There is no one size fits all answer. With the FM diet, you are the one in charge. Any other diet I have been on has been much easier to figure out. Once you get the hang of the FM diet, it's pretty easy. I can eat tons of different foods now. I wasn't stuck on elimination forever.