As a counter to this:
- BG isn't the be all & end all. Other risk factors are generally at least as important, including BP and cholesterol. Any responsible dietary guidance has to take this into account. This is one of the main drivers behind recs like "Eat Well", I believe. If you focus just on BG then you might risk getting not enough fibre, too much sat fat, too much salt, not a wide enough spread of micronutrients etc etc.
- Fibre is really important & this is the main reason for the wholegrains recs. The thinking is that people generally don't get enough fibre and a lot of what they do get is from grains. So recommend wholegrains. (Personally, as a seed fanatic, I think the answer to this one is pretty obvious: seeds are way more nutritious than grains, without the BG impact and with way more fibre.)
- Despite the buzz, many people actually do get their BG under control by following the general recommendations. To the extent they exist, credible studies suggest that any generally healthy way of eating works equally well, with a (vaguely defined) Mediterranean diet generally doing a bit better than LCHF, vegan, whatever in the medium term. This is because at the general T2D population level, the most important thing for getting BG under control is weight loss, much more important than macronutrient composition.
- Restricting carbs in the absence of weight loss generally isn't going to do much for fasting BG levels. There's no credible evidence that carb restriction does anything much to improve hepatic insulin resistance, which drives overactive gluconeogensis, the process by which he liver (mainly) produces glucose from amino acids, trigs etc - not carbs. This process is most apparent overnight and is supposed to be the most characteristic feature of T2D. What does generally work is sufficient weight loss to clear fat from the liver and thereby improve hepatic insulin sensitivity.
- On the other hand restricting carbs does have an obvious impact on post-prandial BG levels and this is important while in the early stages of getting T2D tamed. Things like "Eat Well" fall down to the extent they don't recognise and allow for this. The difficulty is that everybody is indeed different in their response to carbs and you can't make up useful specific rules. If you just say, "cut carbs as much as possible", then you risk people cutting too much fibre and micronutrients and adding too much sat fat, salt etc, and for many people it just won't be sustainable anyway. But if you want to make it more nuanced, you have to recognise that people will have to test often to work out what does what to them, which depending on jurisdiction may fly in the face of anti-SMBG policy and anyway runs into the inability or unwillingness of many T2's to self-test effectively.
- The latest update to the American Diabetes Association guidelines recognises these difficulties, and says in essence: "Eat healthy, and within this manage carbs in personalised consultation with a dietary expert". That's probably the best which can be done at the moment in terms of general guidance, but it's obviously not very satisfactory, for newbies looking for answers and without access to expert one-on-one guidance, or without SMBG support. The ADA commentary is hopeful about the recent high-profile personalised nutrition research - send a stool sample, get back a list of foods to try/avoid. But there aren't any sure-fire answers right now.
