The NHS bases it's information on evidence.
There is also a significant lag between new evidence coming to light and adoption across the NHS.
Added to which , a lot of peer reviewed studies are funded by food manufacturers and their associates. The temptation for people with skin in the game to suppress any evidence which does not support their case and only publish ones which suit their purposes.
Journalists find that reporting simple results make much better headlines than the equivocation of 'under these circumstances...'
Evidence is not just so easy to find.
DH was diagnosed as TII diabetic in 2006. The NHS advice at the time was that it was not reversible , that way of eating had very little impact and to resign oneself that the pills available would eventually become ineffective and insulin injections would become routine.
Fortunately, we found lots of evidence for alternative approaches. Using MN's own low carb high fat bootcamp, which includes really helpful resources, DH lost lots of weight and regularly delivered blood test results in the low, not diabetic range.
At his GP's insistence, he continued the metformin medicine for a full year after the blood tests, before finally (sic) accepting that he was no longer TII diabetic.
They insist on annual blood tests so we know the results have been maintained.
In the time that we have known about the impact of eating low carb high fat on blood sugar, https://www.diabetes.co.uk has started to recommend low carb high fat for diabetics. NHS still has not made any change to their advice. Many more practitioners now agree that the high fat low carb is the way forward and say that we should not expect the NHS to update their advice any time soon.
We are in touch with many, many others diagnosed TII who have followed the same way of eating with the same results.
This is only one area that we know about. There may be others where the NHS lags best practice.