Our blood has a pH balance. In the most alkaline state our body can function optimally. If we eat acidic foods it causes acidity in the body, it's just that simple. When your parents scolded you to eat your fruits and vegetables, they weren't kidding. Acidity causes a variety of diseases.
Cold showers promote alkalinity, whereas hot showers cause acidity due to nerve stimuli. Chemically if we only eat acidic foods, the body doesn't maintain a balance so it dumps the extra acids elsewhere to maintain a pH balance. That area causes cells to die and those dead cells create more acids. The cycle prevails and the cells start to mutate causing the growth of tumors.
In the US alone, Americans go more than two weeks without any alkaline foods eating purely fast foods, fried foods, cheese, eggs, dairy, sodas, other high sugar beverages, processed foods, white flour products such as pasta. Americans are the most obese in the world, with the most diseases and medications used.