The digestive track has different PH levels all along. Kind of a defense mechanism.
First the stomach, very acidic. Then intestines, very alkaline. And then the colon, very acidic again.
Acidic environments kill many pathogens, no doubt of that if you consider what the stomach acids do. Then the colon prefers acidic to kill many pathogens and to encourage good flora which in turn controls the overgrowth of other pathogens that can still survive in low PH.
Yeasts, or at least Candida, do very well on low (acidic) PH, and not so good on alkaline. But strong acids can kill yeasts too (there's a limit to how much acidic conditions yeasts can handle).
So, if you follow the idea:
1 Try to improve your stomach acids. If you need them anyway, better make sure they're strong to help digestion and to kill as much invaders as you can. Helping digestion involves less undigested food that later (mostly in the colon) will feed yeasts.
2. Then, try to eat alkaline foods. KEEP IN MIND there is a difference in the PH level of the food before digestion, and after it starts digesting in the stomach and enzymes are added. This is called the ACIDIC/ALKALINE ASH. So, for instance, fresh lemon juice is acidic to the stomach, but after it mixes with stomach acids and enzymes it becomes alkaline (to be precise, it is not "lemon" as we know it anymore). The small intestine will see the leftovers of this ASH as alkaline.
So again, eat more alkaline ASH forming foods to keep your small intestines more alkaline and discourage any yeasts from taking hold there.
3. Most importantly, no matter what you eat, try that it is well digested and that the leftovers that are able to reach the colon (way at the end) are not undigested food (fiber is one of them, but is so hard to digest for Candida that it is considered "safe"). Undigested carb-rich food will ferment. Undigested protein-rich food will putrefy. This will lower the PH of the colon even more than normal, which will kill many of the good flora species, encourage yeasts to multiply and in turn feed them!! To make it worse, fermenting and putrefying food render toxic waste that will encourage yeasts more, will kill good flora even more, and will make your bowel irritable. AND THE COLON IS CRITICAL, because the flora population there is an average of 1000 times greater than in the small intestine.
Problems that follow: Transit time is disarranged. At some point toxic waste will lower peristalsis waves, causing constipation. Constipation means more time for the food sitting there to ferment/putrefy and the worst it becomes. The body tries to react with diarrhea, which if yeast are not very strong, may suffice (for a while). But if not, then the surface of the intestines becomes damaged by constant diarrhea and flushing. this can create leaky gut.
The worst is that many of this events occur without pain at the beginning, so we do not take it seriously, until it finally hurts or affects another weak part/organ.
The anti-yeast diet was conceived to address and revert this cycle. But it is slow and not always reliable, depending on how strong is the person and how much damage there is to revert.
My personal opinion is that this condition, in individuals without any organic or genetic damage (most of us), is always reversible. the question is "how much pushing" and "how much pushing per day" can we stand for.
If you are asking about PH and yeast in the colon: Yes, yeasts may live in the colon, and be encouraged to, because it is acidic. The difference is, that in healthy individuals, this is normal. The Candida, for instance, is encouraged by the low PH of the colon to live there, but is kept IN CHECK by the good flora, and, if a healthy Diet is regularly followed, the transit time is fast, undigested residues are low, and the COLON ECOLOGY will simply be kept under a healthy balance. But remember, Candida will always be there, it is normal. Another difference is that the Candida in healthy COLONS has very few (if any) detectable colonized space in the COLON walls. When Candida colonizes the walls, then it forms roots and THAT IS where it is difficult to kick out.