The fibre conundrum in IBS


If I stick to this default diet I don’t have any IBS symptoms the next day

breakfast: Steamed zucchini, carrot, string beans
lunch: salad (cucumber, carrot, gherkins, olives, tomatoes) with avocado
dinner: a small amount of meat or seafood with vegetables only – any of these: pumpkin, broccoli, string beans, zucchini, choko

But this is so hard to do day after day and it’s hard to feel full on Paleo unless you eat a lot of meat, which will make things worse (eating too much meat causes an excess of sulphur that produces hydrogen sulphide gas). On days that don’t matter or weekends I basically eat what I want – which is usually pizza, cakes, milk etc.

What I’ve found over the last few years is that wholegrains cause the worst IBS. On the other hand, pizza and cakes don’t cause much in the way of symptoms at all, apart from evacuation taking 2 or more hours the next day. But the gas itself was minimal. I don’t think it’s to do with fibre, as my safest diet has a lot of fibre in it.

I think it’s to do with anti-nutrients. This is how it works with wheat:

The wheat kernel has 3 parts to it – the endosperm (the starch), the germ (the seed that makes a new plant) and the bran (mostly insoluble fibre).

The germ contains Wheat Germ Agglutinin (WGA), one of the very troublesome proteins. WGA is a glycoprotein called a lectin. Plant lectins are designed by nature to attack the cell membrane of any predator who tries to eat them. Lectins bind readily to sugar and can attack any cell membane with a sugar coating. The microvilli of our small intestine (through which we absorb our carbs) are lined with a sugar coating called glycocalyx. WGA can directly damage this tissue. This can cause all sorts of problems. This will affect how well we can digest our carbs, but also if WGA can breach the gut barrier this can cause Leaky Gut, where wheat proteins can escape into the blood stream where they don’t belong. This can initiate an innate immune reaction and lead to inflammation.

(That other noxious protein, gluten, is in the endosperm, so all wheat has this unless it’s “gluten-free wheat” – the gluten can supposedly can be rinsed out. Gluten causes intestinal permeability to some extent in everyone, not just Celiacs).

Refined flour – pizza, crumpets, white bread etc are mostly endosperm. The germ is discarded so refined flour has a lot less WGA than wholewheat. Refined flour though is almost all glucose, and is high GI.


White rice is the endosperm of rice and is relatively free of anti-nutrients. Brown rice includes trypsin inhibitors. These inhibit the enzyme Trypsin that breaks down protein to its constituent amino acids.

White rice, like white flour, is almost 100% pure starch (glucose). These are still very unhealthy foods, but in their refined form they lack the toxic anti-nutrients that work against digestion.


All oats are wholegrain; you can’t get refined oats. Oats contain anti-nutrients – as do all grains – e.g. the gluten avenin as well as saponins, chemicals that can penetrate and damage the intestinal wall.

So any wholegrain for me causes the worst IBS the next day, but not refined flour.
Legumes and white potatoes are high in saponins that can attach to and damage the intestinal lining.

I can’t tolerate wholegrains at all, yet I can easily digest salad and certain vegetables. Fibre isn’t generally inflammatory. So it might not be the fibre as such that is the problem, but the anti-nutrients within the fibre.