Not an expert but you just have to look at all the internet forums out there where people post about their stories. There are thousands of testimonials - all of people who have their diabetes under control and have been able to come off medication, and others with really perfect blood sugar levels, blood fat levels, blood pressure, etc. etc. I know it's really hard to get your head around the idea that fat = healthy but there is so much anecdotal data and scientific fat which says this is healthy
And if we survived for thousands of years eating this way, it can't be unhealthy.
For me, as a diabetic, this is how I will eat for life. I eat low carb/high fat and have lost weight, lowered my cholesterol and lowered my hba1c (which is the standard by which my diabetes is measured and means I have stable sugars and much tighter control than I used to).
The diabetic dietary advice is currently under review, and I hope that they are going to change their advice about carbs. There is lots of info here about diabetes in particular and carbs. I strongly believe that in the longer term, the general dietary advice will be updated for everybody, whereby sugar is the thing to be most careful about rather than fat if that makes sense.