The much simpler explanation is they're both caused by carbohydrates and especially sugar.
Which does look initially promising:
> Giving the mice a drug that binds gingipains cleared P. gingivalis from the brain better than a common antibiotic, and it reduced the β-amyloid production and resulting neurodegeneration. [...] In initial tests with human volunteers, a similar drug seemed safe and showed signs of improving cognition in nine participants with Alzheimer’s, the company says.
Also, did you miss the distinction between a cause and the cause? It's not a zero-sum game.
More seriously, yes, I agree that sugar is nasty, but it's a bit too simple to blame it as the sole factor for all possible diseases that have a mechanism of action that hasn't been clearly identified.
It appears that the simplicity of the explanation is itself a problem. Surely - all these chronic diseases can't be that simply explained? Dr. Wahls essentially claims carbs are the root cause of MS, which she cured in herself (with the corollary that carbs eliminate other nutrition). Dr. Fung claims it's the root cause of diabetes. Prof Seyfried claims it's the root cause of cancer. It surely can't be that simple?
Reading all their work, and others, I'm struck that it's very much a five-whys scenario[1].
Also there are two points wrapped up in the original response. One is about the cause, but there's a bigger issue about the avoidance of the problem in a first place. If someone never eats refined carbs and therefor avoids the root cause, why would they care about the details of the cause? We care about the details insomuch as we would like to treat the disease, but today we can't do that. On the other hand we do know with a lot of certainty that eating well, fasting and exercising are good for us and avoid the problems in the first place. For some reason, that doesn't matter as much.
The downside with treating the disease is that you also enable it, like how we "treat" T2 diabetes by essentially just giving you more diabetes via insulin shots.
[1] - https://stevecoast.com/2015/03/27/the-world-will-only-get-we...
I figured there's always enough bacteria in the mouth to cause morning breath, food consumption or not, but there is definitely an exacerbation of mouth bacteria from food consumption.