Stuff like this is about as close to trans acceptance as Japan gets. Weird that a culture which is so big on femboys is so behind on accepting trans women.
Also, yeah, prior to western intervention, Japan ironically had some of the worst nutritional diversity among similarly developed nations. They barely innovated their cooking methods and most people thought that you could eat only rice and be healthy. Malnutrition was so common that Japanese people used to think it was a normal disease. Even when they had enough food to eat, they just only ate rice, radishes, and foraged seasonal food like berries and fruit. Villages that farmed wheat or barley were also generally better off, because wheat is a much better source of nutrition than rice. Especially considering yield per hectare.
The malnutrition obviously doesn't include fishing villages, who would need to try very hard to be malnourished. A diet of only fish, seaweed, shellfish, vegetables, and whole grains is basically a power diet. Thinking about it, you often see a common trend in Japanese media of people with "weak constitutions" moving to coastal towns because "the air is better" or other stuff like that. I'm willing to bet this superstition arose from this.