I agree that eating in a healthy way (lots of fresh fruit and vegetables, sources of complex carbohydrates, fish, lean meat, nuts, eggs, etc) combined with minimal intake of sugar and processed foods is a great plan.

However, this does not have anything to do with the pH of body fluids, which is usually controlled by well-understood physiology. Sometimes the pH of body fluids can be abnormally low - this is called acidosis. Most commonly it reflects lung problems ("respiratory acidosis") or kidney problems ("metabolic acidosis") - Acidosis: Causes, Symptoms & Diagnosis.

While eating in a healthy way is good, this has nothing to do with the pH of body fluids - The Alkaline Diet Myth: An Evidence-Based Review.