I agree with your general point. On the other hand my diagnosis A1c was 104 just after my 80th birthday. It was down from 32 after 6 months on a diet of protein and vegetables. Mark you I had been seriously overweight and wanted to get back to normal.
As
@Maz2 is underweight it's a different situation. Even so dietary changes may be possible. Maz2, why not compare your diet with the ones I just mentioned above:
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David Unwin's Norwood Surgery low carb diet sheet
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Zoe Harcombe's 'What should we eat?'
and Freshwell's advice, a model of clarity.
I find Cronometer (free version) invaluable to keep track of my nutrients.