Complex carbs, or vegetables, whole grains, nuts and whole fruits are often no better, when it comes to people battling SIBO. This is because complex carbs contain fiber, which is actually made of sugars that are NOT digestible by our bodies. The cellulose fibers that give plants structure are actually pure sugar, but the bonds that hold these sugars together cannot to broken down by our enzymes. This makes them insoluble fibers … which simply means that they are not very soluble in water.
Insoluble fiber is crucial in our diets, but to much of a good thing is not always good, especially for people that have increased intestinal transit times (taking longer for food to transit the gut), are under a lot of stress, have genetic factors that result in leaky gut or food allergies, along with bacterial overgrowth. So what I am trying to say is that salads and raw fruits are essentially bad for people with SIBO!
Having slammed insoluble fiber for people with SIBO, I should digress and state that the goal of a balanced diet, once the bacterial overgrowth is treated and the intestinal lining is restored, is to have a diet high in diverse types of fiber. Fiber is what feeds the various bacterial populations in a healthy gut, but it is important to be careful not to eat to much of the wrong fiber and feed to many of the wrong bacteria.
High soluble fiber is another animal (, but really a plant,) all together. Soluble fibers are mostly made of pectins which bind to water extensively. This is what makes whole grains (oatmeal, brown rice, whole wheat, potatoes, ground flax seeds) along with nuts and apples sticky when mixed with water. The soluble fibers are not as rough on the intestinal lining as their insoluble cousins, but they still produce a similar dilemma when it comes to SIBO.
Soluble fibers again have bonds that our digestive systems cannot breaking down. Again this the simple definition of fiber. The difference is that soluble fibers expose more areas for water and other polar molecules to bind to and the foods that they contain generally have more starches that our bodies and bugs can breakdown and access as sugar.
Soluble fibre can produce two problems for people with SIBO. Like its insoluble cousin, soluble fibre is a readily available food source for bacterial overgrowth because the bacteria have key enzymes that can access the sugars from which the fiber is made. Secondly, although soluble fiber has the ability to bind water, it can also loss water through the small intestine and into the large bowel, which can actually increase the risk of constipation. Just leave your oatmeal on the counter for a while. Initially it is a nice, soft goo, but eventually it turns hard and crusty. The same thing happens to other whole grains, like rice or wheat as water is lost.
In the end, both types of fiber are a double edged sword for SIBO. In one sense they provide food for healthy bacteria to grow, which in turn provides the food for healing our intestines. On the other hand insoluble fiber is rough and abrasive which can damage the intestinal lining and soluble fiber can worsen constipation, all while feeding your bacterial overgrowth. The objective needs to be to restore balance to the gut and then introduce a diverse amount of fiber (often with probiotics) that can support the recovery of the intestinal lining and in turn the immune system it houses.