Some people just don't break down certain foods that are on the FODMAP list well, and that causes GI tract havoc.FODMAPs (which stands for fermentable oligosaccharides, disaccharides, monosaccharides and polyols) are short-chained carbs that include fructans, lactose, fructose, sorbitol and mannitol, according to Harvard Health Publishing.The poorly digested fructose gets fermented by gut bacteria, says Ray Scott Daugherty, MD, who specializes in treating all colorectal diseases, which can lead to upset stomach symptoms including:.Poor absorption of fructose is thought to be one of the dietary triggers for irritable bowel syndrome, and could be the reason why tomatoes give you diarrhea.So if you were wondering why tomato sauce gives you diarrhea or hurts your stomach, these ingredients could be to blame.Tomato soups and juices can also have various additives your stomach doesn't agree with, so don't forget to read labels.Fix it: If symptoms become problematic, it's best to have your doctor or a dietitian help you plan a diet around your restrictions so you can avoid upset stomach and diarrhea after eating tomatoes.A small 2013 study in the Journal of Investigational Allergology and Clinical Immunology concluded that tomato allergy happens from an overreaction to certain proteins in the fruit.In response to these proteins (the allergens), antibodies, histamines and other chemicals are released into the bloodstream, which cause allergy symptoms.According to dietitian Ashley Kravitz, RD, owner of Nutrition Specialists of New Jersey, these symptoms might include the following on the skin or mouth:.If you have any of the above symptoms after eating tomatoes, see your doctor or an allergist, who can help you figure out the root cause.Warning If you have difficulty breathing, trouble swallowing, a swollen throat, chest tightness or severe hives, seek immediate medical attention, per the Mayo Clinic.It's an uncomfortable burning sensation in your chest due to an irritated esophagus that's caused by stomach acid.And food poisoning from tomatoes can cause diarrhea, along with upset stomach and the following other symptoms:.Botulism is a serious type of food poisoning that's caused by a toxin that attacks the nerves in your body and can lead to paralysis, per the Centers for Disease Control and Prevention, but can also induce stomach issues such as vomiting, nausea, diarrhea and stomachache.Warning See a doctor immediately if vomiting and diarrhea last more than two days, you have bloody stool, a high fever, confusion, worrisome stomach pains or signs of botulism (muscle weakness, headache, blurred vision, upset stomach and trouble breathing), per the Mayo Clinic