I was reading a book by Professor Arnold Ehret called Mucusless diet healing system.
Ehret was a brilliant man who did many experiments and came to the conclusion that the natural diet of man was fruits (raw or cooked), greens, and above ground veggies.
He and his disciplines achieved perfect health on this diet to almost unheard of levels.
A women disciple of his spoke of some of the changes to her health on this diet from health she considered good already having been a vegetarian for years.
Some of those I still recall though I have not read that part again for at least 20 plus years were her skin became as soft as a baby, she had more pep than when a child, all kinds of small things got better, she had a much pep after 8 hours on her feet working as a waitress all day as when she arrived, she could walk up steep hills that others had to rest frequently barely noticing it was uphill with no hard breathing at all and her entire personality changes..she became peaceful, calm, happy, kinder etc so much so that all she came in contact with mentioned this huge emotional and personality change in her. She talked of three incidences were huge amounts of mucus came up as Ehret said they would This in general happens as the mucusless diet removes mucus from the diet causing many diseases.
It was the earliest book on health but one I recall reading decades ago. Ehret was born in the 1800s and died from a fatal accident in 1922 but was a forerunner to the raw food diet I would say.
Well having a current health challenge I pulled this book out again
Most of Arnold Ehret's book are found free online here
Here he talks of the spongy organ of the kidneys (and liver) are sort of like a sieve and thus can get easily clogged with the sticky mucus of the wrong food. You might want to look at some of his other books there if interested.