According to the theory of Natural Selection, genetic adaptation would have caused our ancestors to become predisposed to digesting foods available in the region they lived in. It has only been a couple hundred years since large-scale shipping companies started distributing foreign foods regularly, which in evolutionary terms is practically the blink of an eye. This means that depending on your genetic makeup, there are likely some foods you can digest and assimilate much easier than others. For example, milk is easily digested by infants because they produce the enzyme lactase, which digests lactose. However, a large population loses the ability to produce lactase after weaning. When lactase isn't produced in sufficient quantities, consuming milk will often produce fermentation (gas), bloating, diarrhea, and a whole host of other symptoms that may not even be apparent unless milk has been eliminated from your diet for a while.
The same thing can happen with other potential allergenic foods. The list would include wheat, legumes, refined sugars, industrial seed oils and overly processed food. Therefore, I recommend a period of utilizing an elimination diet to anyone who aspires to be truly healthful. The premise of an elimination diet is to remove any potential source of food that could induce an intolerant reaction or inflammatory response, slowly reintroducing possible offending foods one at a time and paying attention to their effect on your digestion and overall well-being. This makes it possible to identify any reactions to a particular food.
For example, before harvest, wheat seeds are hardening themselves up for winter. This makes them extremely hard to digest, which can trigger the gut to produce an inflammatory protein called Zonulin. First discovered in 2000 by Gastroenterologist Alessio Fasano of Massachusetts General Hospital, Zonulin was found to help regulate leakiness in the gut by opening and closing “tight junctions” between cells in the lining of the digestive system. Normally this response protects us from harmful bacteria by inducing diarrhea to flush pathogens out of our systems, but this causes even more extreme permeability in sensitive individuals. Intestinal permeability, or “leaky gut” can allow fecal matter to leak into the blood stream, which triggers potentially chronic inflammation. The immune system recognizes the offending particles and attacks them as if they were a foreign invader or disease, causing inflammation to prevent further intrusion. Taking it a step further, the immune system might look at cells elsewhere in the body and recognize them as being similar to the cells it took out of the blood stream, causing an inflammatory reaction that can lead to a host of diseases.
Other foods that need to be considered include refined sugar, which causes an insulin spike and subsequent crash that can lead to chronic inflammation as well. Depending on individual response, this can also happen with the consumption of excessive amounts of carbohydrates in general, especially without prior exercise. I would also advise to be aware of consumption of certain legumes. Certain legumes can be harder to digest than others for some individuals. Beans, beans the musical fruit, right? For example, red Lentils seem to be easy for me to digest in particular, while I have big problems with black beans. Any symptoms that arise when adding these foods back into your diet could be a signal that your body is having trouble digesting and assimilating them.