Crab and watermelon are both cold foods, it is usually not recommended to eat watermelon immediately after eating crab, especially for people with certain impairments in their gastrointestinal tract, so as not to have a certain impact on the gastrointestinal tract, increasing the burden on the gastrointestinal tract, and may even cause abdominal pain, diarrhea and other adverse reactions in some people, so after eating crab, it is recommended to eat watermelon after an interval of time. If you eat a lot of watermelon immediately after eating a lot of crab, it will also affect the absorption of protein, calcium and other nutrients in the crab, reducing the nutritional value. In addition, if you are allergic to seafood, you may not have an obvious allergic reaction after eating crab, but if you eat a lot of watermelon immediately, it may lead to an aggravation of the allergic reaction and cause dizziness, weakness, nausea, vomiting, fever, and rash and other allergic symptoms. Therefore, it is recommended to eat crab for 2-3 hours before eating watermelon to avoid the above-mentioned adverse reactions.