On a hot summer day, as people eat more watermelon, so do the sayings. Some believe that watermelon causes "heatiness" (上火) because it leads to constipation, while others believe it "cools the body" (败火) because it causes diarrhea. Nutritionists say that watermelon is sweet in taste and cool in nature, clearing heat and detoxifying, relieving vexation and quenching thirst. It has a diuretic effect and is rich in nutrients, making it an excellent food for beating the summer heat and certainly not a cause of "heatiness." So, what's the deal with constipation and diarrhea? Watermelon is diuretic but not laxative.
Director Yu Guixiang, head of the Nutrition Department at Beijing Chaoyang Hospital, gave an analogy: place a fresh radish in very concentrated salt water, and over time, the radish will wilt. Why? Because the salt water draws the water out of the radish due to its high osmotic pressure. Sugar, just like salt, has this osmotic property. Watermelon has a high sugar content. For some people, especially those with poor sugar absorption, eating too much can create this high osmotic state in the body: the cells' ability to absorb water is less than this osmotic pressure. As a result, water from the ingested food and from the cells is drawn out and excreted, causing osmotic diarrhea.
This same principle can occur in the urinary system, which is the reason for watermelon's osmotic diuretic effect. As for constipation, Professor Han Ying, Vice President of Beijing Military General Hospital and Chief Physician of Gastroenterology, believes that while watermelon is a diuretic, it is not a laxative. After eating too much, the body's water is excreted through urine, leaving less water entering the intestines. Coupled with factors like mental stress and a low intake of dietary fiber, it's not hard to understand why some people experience dry stools or even constipation.
It's best not to eat watermelon that has been refrigerated.----Eating iced watermelon harms the spleen and stomach----In the summer, many people like to put their watermelon in the refrigerator to get it ice-cold before eating. While this feels good on the mouth, it can cause significant harm to the spleen, stomach, and throat.
Generally speaking, for people with normal gastrointestinal function, eating a lot of watermelon won't cause constipation or diarrhea. However, it's not uncommon for people to suffer from various gastrointestinal inflammations. Coupled with mental factors like work stress and irregular lifestyles, many people now have Irritable Bowel Syndrome (IBS). Director Yu Guixiang says that the cases of constipation or diarrhea after eating too much watermelon often occur in these groups of people because the high osmotic nature of watermelon can easily alter the gastrointestinal motility in such individuals. It seems that "constipation and diarrhea" are not the fault of the watermelon; rather, "poor gastrointestinal function" comes first, followed by "constipation and diarrhea." Therefore, for these people, it's best to eat less watermelon, or not at all, or to eat it in smaller portions. It is best to avoid eating watermelon that has been refrigerated. Expert Advice
Eating watermelon to beat the heat has taboos----Watermelon is a great food, but it has its taboos. Watermelon is a raw and cold food, relatively cool in nature. Therefore, people with a weak constitution, those with heavy menstrual flow, chronic gastritis sufferers with poor digestion, and the elderly should not eat too much of it.
Due to watermelon's osmotic diuretic function, Director Yu suggests that people with "heatiness" conditions such as a sore throat, mouth sores, or urinary tract infections can eat more of it. The diuretic effect of watermelon can help "cool the body" (败火). Additionally, watermelon is also beneficial for people with high blood pressure and poor kidney function.