Source for this? My understanding is that the link between non-caloric artificial sweeteners (NAS) and diabetes is growing increasingly clear. For instance:
NAS linked to glucose intolerance (pre-diabetic hyperglacemia): https://www.nature.com/articles/nature13793
NAS unlikely to be healthy alternative to sugar for prevention of type 2 diabetes: http://www.bmj.com/content/351/bmj.h3576.full
Second one: I haven't read the whole study but they categorize fruit juice which is chock full of sugar along side artificially sweetened drinks - which is a red flag to me. Also, I don't think people who swap sugary drinks for diet drinks and changes no other aspect of their diet will have a better outcome in regards to type 2 diabetes. It doesn't mean that diet sodas contribute or cause type 2 diabetes.
> Big Sugar has paid researchers to conduct misleading — if not false — studies about the health effects of added sweeteners.
The core issue is not the type of sugar, but the nature of it being basically everywhere in packaged foods.
The author also mentions that it's not worth trying to quantify the amount of sugar:
> Don’t agonize over the sugar content of every single thing you eat.
I find the best rule of thumb is to "eat around the outside" -- most American supermarkets push produce, meat, dairy, etc., to the outer walls of the market, and design stores to make you criss-cross the packaged goods aisles in the center. If you focus shopping on fresh foods, you generally will eat better (with a slightly more expensive grocery bill).
Note that although artificial sweeteners like stevia and erythritol don't raise the blood glucose at all and have GI index of zero or near zero - some artificial sweeteners actually do raise blood glucose, like maltitol etc, and these sweeteners are unfortunately often found in sugar-free candy. You can try a web search for "GI index artificial sweeteners" to see a list of sweeteners that have low GI score.
Something else to keep in mind is that over consumption of very carb heavy products like bread or pasta will have the exact same effect on your blood glucose as just eating sugar.
If you're talking about a neutral pH as in pH = 7.0 (the usual accepted definition of neutral), these claims are contradictory. The pH of the human blood is usually between 7.35 and 7.45. This is usually way less acicic than the neutral pH of 7.0. Furthermore, a pH of 7 is usually associated with very serious disease (and yes, it is causal: if you inject/ingest enough acid to make the pH drop to 7.0 you're in pretty bad shape, especially because it means the regulatory mechanisms aren't working as they should). I don't know who that "professional nutritionist" is, but this sounds like crackpot-level science.
Also, to the best of my knowledge, it's extremely hard to change the blood's pH with diet... The body has a multi-layered system specifically dedicated to keeping the pH in the normal range (7.35-7.45), and that's independent of what you eat. Maybe you're mistaking it for changing the urine's pH, which is much easier to do, and can be achieved through diet alone. Unfortunately, changing the urine's pH doesn't seem to achieve much beyond preventing some inds of kidney stones...