70-year-old man hospitalized after eating half a watermelon

Asia University Hospital Peritoneal Dialysis Room Director Lin Xuan-ren stated on his Facebook fan page "Inviting the Kidneys · Dr. Lin Xuan-ren" that he encountered a case: "Dr. Lin, a 70-year-old male patient, was so short of breath that he couldn't lie down, his legs were swollen and shining, his blood oxygen was only 88%, and his chest X-ray was foggy. His kidney function had also failed." I looked at the monitor by the bedside, then at the old man's shining swollen calves. When I pressed down, the indented fingerprints took a long time to disappear. "How much watermelon did you eat?" I asked softly. "Probably half a watermelon," his daughter said quietly. "The weather was hot, and he loves to eat it. We thought it was just fruit, how could anything happen?"

Lin Xuan-ren said that the old man was a long-term patient with chronic kidney disease stage five. He had strictly instructed him to control his daily water intake to within 1500 milliliters, and he was afraid to even drink soup. But "watermelon" was considered fruit and a way to relieve summer heat in his understanding. That night, the old man was rushed to the intensive care unit, given diuretics, and put on a non-invasive positive pressure ventilator (BiPAP). He struggled until the next morning before he could slowly lie down. Every summer, such stories repeat themselves in the nephrology ward several times.

Lin Xuan-ren stated that watermelon has a water content of up to 92%. Converted to volume, this means a medium-sized watermelon weighing five kilograms contains nearly 4600 milliliters of water, which is more than an adult male's daily water requirement. Even if you only cut a quarter, that's over a liter of water; if you cut it into thin slices for a typical family to share, eating five slices would easily exceed a thousand milliliters of water.

Lin Xuan-ren explained that for people with healthy kidneys, excess water is easily excreted through urine, so they feel cool and refreshed no matter how much they eat. However, for patients with chronic kidney disease stage four or five, or those who are regularly undergoing dialysis, the kidneys are like a semi-paralyzed pumping station. Water that comes in cannot be expelled and accumulates in various parts of the body. When it accumulates in the legs, it's called lower limb edema; when it accumulates in the abdomen, it's called ascites; and the most dangerous is when it accumulates in the lungs, medically known as "pulmonary edema." Its symptoms include shortness of breath, coughing up pink frothy sputum, and inability to lie down, which is also the main reason many kidney patients are sent to the intensive care unit.

Lin Xuan-ren pointed out that watermelon hides another silent killer: potassium (potassium). Every 100 grams of watermelon contains about 112 milligrams of potassium.

Strictly speaking, watermelon is not a high-potassium food, but this amount doesn't sound like much. However, watermelon is so easy to eat one slice after another. A normally cut slice of watermelon is about 150 grams, containing about 168 milligrams of potassium; eating five slices would be close to 840 milligrams; if, like the old man, you ate half a watermelon with your family in the yard, the potassium intake would directly surge to 3,000 milligrams.

For ordinary people, excess potassium can be excreted through urine without causing problems. However, for kidney patients, it is medically recommended that daily potassium intake should not exceed 2000 milligrams. Half a watermelon would exceed the entire day's limit. The danger of hyperkalemia lies in its almost complete lack of obvious warning signs.

Initially, it might just be numbness in the hands and feet or muscle weakness, which can easily be mistaken for "heatstroke" or "fatigue." However, when blood potassium levels exceed 6.5 mEq/L, heart rhythm disturbances begin; once it exceeds 7.5, the heart may stop directly without warning. In the emergency room, I have seen too many kidney patients brought in by their families who could no longer feel a pulse.

Therefore, for kidney patients, the "deliciousness" and "danger" of watermelon are almost synonymous: the sweeter and juicier it is, the more likely it is to lead to unintentional overconsumption; the larger, colder, and more refreshing it is, the more it hides unseen water and electrolytes. It is not simply a piece of fruit, but a small reservoir filled with water and potassium ions.

How to eat watermelon safely? Lin Xuan-ren stated that one must understand "portion size" and "timing." For kidney patients who have chronic kidney disease but are not yet on dialysis, my recommendation is "just one slice." A slice is about the size of a palm, about one finger joint thick, and weighs between 100 and 150 grams. This slice of watermelon contains about 100 milliliters of water and about 168 milligrams of potassium, which is within the safe range.

However, the prerequisite is: you haven't had soup today, you haven't eaten other high-potassium fruits (bananas, kiwis, cantaloupes also count), and after eating this slice, you must "count its water content into the total daily intake." In the afternoon, you must resist that cup of bubble tea.

For kidney patients who are regularly undergoing dialysis, the principle is stricter: try to eat a small slice on the "day after dialysis." This is because after dialysis, the water and potassium in the body have been removed, leaving more room to accommodate. On non-dialysis days, especially for those whose weight has already increased by more than 5% between two dialysis sessions, or who already have edema or shortness of breath, put the watermelon aside for these few days; it is not a treat for you, but a burden.

Lin Xuan-ren proposed three "don'ts" for kidney patients eating watermelon:

Don't blend watermelon into juice: A glass of watermelon juice often concentrates the water and potassium of nearly a pound of watermelon, and because there is "no chewing sensation," it is consumed in one gulp, and the body absorbs it all before it can react.

Don't have unlimited refills as fruit after meals: The most common scene in Taiwanese families is a large plate of cut fruit placed in the living room after dinner, and everyone eats while chatting. Kidney patients are most likely to lose control in such situations.

Don't sprinkle salt on watermelon to enhance sweetness: This is a double blow to blood pressure and fluid control.

Finally, I want to say one thing to all the families of kidney patients: concern for kidney patients is never about "eating a little more," but about "helping him cut a slice." Please cut the large watermelon at home, put a small plate for the kidney patient in front of him, and enjoy the rest yourself.

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