The most common cause is poor-quality food, the storage conditions of which have been violated. Very often, tourists buy food in cafes and restaurants, as well as in small kiosks on the beach. There are not enough conditions for food to stay fresh for a long time.
Rotten fruits can be another reason. He advised me to eat something that does not need a refrigerator, such as snacks. He advised to buy everything else in places with powerful refrigerators.
In no case should you drink water from reservoirs or pools, you can also catch an infection from there, so the doctor advised you to always carry bottled chilled water with you.
Also, don’t forget about personal hygiene. In the summer, you need to carry an antiseptic with you, since without cleaning your hands you can catch dysentery from asymptomatic carriers.