In addition to meat, wheat, dairy, and diet sodas, there are certain other foods that can pose problems for people who have digestive issues even though these foods are approved on the Paleo Diet. In general, these are foods that reduce the integrity of the lining of the small intestine, allowing entry of substances that trigger inflammatory reactions.
The way chemicals in these foods cause problems for Paleo dieters who have Crohn's disease or inflammatory bowel disease is by mimicking the offending proteins in meat and wheat. The immune system can't tell the difference between these foods and other foods that trigger symptoms and digestive upset (pain, diarrhea, cramps, vomiting, bleeding, and the like) results.
Alfalfa spouts, amaranth (the leaves of the amaranth plant), and quinoa (the “grain” of the amaranth plant) all contain saponins. In sensitive individuals, these saponins can cause either clotting or bleeding in the gut. In people who have lupus, alfalfa sprouts can trigger a kidney-toxic reaction.
Beans and legumes, especially if they are eaten raw, contain a group of generally toxic compounds known as lectins. In nature, lectins discourage grazing animals from eating an entire stand of legumes. Some seeds survive so the plant can reproduce. In the human diet, lectins trigger inflammation in the gut that results in flatulence and either diarrhea or constipation, but in some susceptible individuals lectins can also break down red blood cells.
Beans and legumes also contain phytohaemagglutinins, which can trigger the multiplication of white blood cells in the lining of the intestine. White blood cells cause the inflammation characteristic of Crohn's disease, inflammatory bowel disease, and possibly irritable bowel syndrome.
Egg white, previously mentioned for its addictive qualities, contains a group of enzymes known as lysozymes. These enzymes interfere with potassium regulation, so there can be fatigue, muscle weakness, and slow reflexes–along with a general tendency to eat more.
Chili peppers contain a burning compound known as capsaicin. While capsaicin actually does not aggravate gastroesophageal reflux disease or heartburn (it's actually the amount foods consumed with the chilies that causes acid reflux), it can causing burning diarrhea.
Potatoes aren't on the Paleo Diet, except on “cheat days.” The peel, especially if green, can contain toxic amounts of chaconine and solanine, which can nausea, vomiting, diarrhea, burning in the throat, fever, dizziness, hallucinations, and even death. The potato generates these chemicals to prevent animals from eating it when it is about to sprout (when it turns green, the green color due to chlorophyll, which is non-toxic). Any green part of the potato contains toxic doses of these chemicals.
Root beer extracts contain quillaja, which can stimulate the immune system. In Crohn's disease and inflammatory bowel disease, an overactive immune system is the driving force of the condition.
Tomatoes contain a compound known as tomatine. (It's a lot more abundant in the leaves and stems, but also present in the fruit.) This compound can be purified so it can be used to precipitate cholesterol out of the blood samples. In the gut, it makes the cells lining the intestine clump together so they cannot absorb water or nutrients. The body is deprived of fluid and nutrition, and the nutrients are left to ferment in the gut.
Even healthy people can experience digestive problems when they eat these foods in excess. If you have almost any chronic digestive problem, it is best to leave them alone, even when they are otherwise permitted on your diet.