They successfully shifted blame from sugar to fat as cause of modern lifestyle diseases for last two decades. Would highly recommend the book "Case against Sugar" by Gary Taubes discussed amply here[0] and here[1].
Also recommend the documentary "Super Size Me"[2] a revealing take on workings of fast food industry.
[0]https://news.ycombinator.com/item?id=12480733
Fat (not necessarily the stuff you consume but the build up in your body) has regulatory properties for your insulin uptake and thus levels which generally result in more fat == more production needed which will give a more quick rise to diabetes type 2 due to a runaway competition.
In my experience, totally anecdotal, (I have type 1 diabetes since I was about 5): If I gain weight the amount of insulin required by injection is significantly more than what is to be expected by the simple weight gain (e.g. more stuff == more required to control it, you'd expect some linear correlation).
While true; until I see studies showing otherwise, I'll assume that becoming overweight is overwhelmingly caused by sugar though, with few exceptions. And if that assumption holds, the cause is sugar regardless.
Someone with insufficiently treated type 1 diabetes can have very low insulin levels, sky-high blood sugar levels, and be losing weight (and seriously unwell).
Sure, but that's like saying that it's not the size of the hole in the boat that is sinking the ship, but the capacity of the guy with a bucket shoving water out of the boat.
If you can't produce enough insulin to lower your blood sugar to avoid glucose toxicity, you're already sick. So while the insulin is technically storing the fat, the sugar is directly/short term controlling the insulin response, and indirectly/long term your insulin resistance.