Why are the Japanese so worried about the temperature of their tummies?

…as seen in pajamas for kids with huge waist bands and similar waist bands that can be worn under other clothes.

I’m pretty sure that location comes from the Chinese idea that the chi (Japanese ki, a kind of lifeforce), lives in the stomach. It must be said, though, that most cultures have an idea that keeping one particular part of the body hot or cold has almost magical effects on the whole body. My wife was mystified by characters sticking their feet in bowls of hot water in Sean the Sheep and the more recent Western belief that keeping your head warm is enough to keep all of you safe from cold weather has also recently be disproved.