Its the intra and extra cellular fluids of the organs and tissues that should be more on the alkaline side.
Stomach acid is an extracellular of the stomach, which is an organ. And if intracellular fluids need to be alkaline then how do we maintain the pyruvic acid, malic acid and citric acid needed for ATP formation within the cells?
And that does not mean more is better. If these fluids are not in balance, that does not necessarily lead to death. It can lead to poor health.
Well a good diet is more where people have issues with. A good diet according to them consists of mostly fresh fruits, vegetables, nuts, and seeds. Very little meat, cooked foods, or grains.
Scientific fact that diet is insignificant to pH?
Depends on pH of what. Of the blood? Not really. Of the lymphatic system? No. Of the intestines? Not unless you count the fibers needed for the acid formation. Of the intracellular fluid? Well again what forms the acids needed for energy production within cells? Of course it could also be argued that the fatty acids and amino acids in our diet affect many things in our body including pH. For example amino acids are broken down in to highly alkaline ammonia, which is then converted in to uric acid.