Starch is definitely a problem food for me. I suspect most people with IBS have difficulty digesting starch, as well as FODMAPs and meat. There are a lot of commentators on the web promoting starch and in particular resistant starch as a means of healing the gut. These people are usually not talking from an IBS perspective. In my experience on IBS boards, very few IBS sufferers can tolerate starch in any large amounts, and particularly not from heavily processed forms like potato starch.
In general and for most non-IBS people, fibre and Short Chain Fatty Acids (SCFAs) are beneficial to the colon. Starch contains 2 types of polysaccharide: amylose (about 20% of starch) and amylopectin (about 80%). Resistant starch (RS) is the amylose type, which resists digestion. This form of starch travels through to the ilium, the last section of the small intestine, and the colon, where it is metabolised by bacteria. RS is a form of fibre. Fermentation of RS by bacteria creates SCFAs, which are very beneficial to colonic health.
One problem with IBS is that we’re never sure whether or not we have SIBO. RS could exacerbate symptoms by producing even more gas in the small intestine, where gasses don’t belong in any large quantity. An overabundance of gas in the small intestine causes inflammation. An IBS cure involves reducing, not increasing, gas and inflammation. It is only after a successful IBS diet is found that more high starch and high FODMAP foods are gradually introduced. You can’t hurry this step.
Even without SIBO, not everyone can digest starch efficiently. Starch digestion needs a salivary amylase enzyme (AMY1). Some of us have more copies of this gene than others. Those with fewer copies might have a problem digesting starch.
Different forms of starch might be more problematic for IBS. Grains are very high in starch, whereas sweet potato has much less and salad vegetables even less. Each of us has our own individual threshold for starch tolerance.
Common sense has to be your guide here. Do you believe copious amounts of gas are a sign of health, or an indication of inflammation? Once you have found your ideal IBS diet, which will probably be similar to mine, then the trick is to find what healthy foods you can gradually add to your diet. But this needs to be carefully done.