Certain people who are allergic to tomatoes can experience an upset stomach among other symptoms. Food allergies can range from being very mild to extremely severe, depending on the person.
If you eat fresh tomatoes and experience nausea, it could be that you are at least slightly allergic to them. The high acidity of this vegetable is another explanation for why some people have upset stomachs after eating them. Foods like tomatoes that are high in acid tend to affect people’s acid reflux/heart burn, causing a burning and/or nauseas feeling to occur.
If you experience any severe stomach pain after eating a tomato, it is highly recommended that you contact a doctor right away.