I am certainly not a nutritionist or an SS coach but something seems funny here. You didn't mention any medical tests. It's difficult to properly gauge a real gluten intolerance vs. poor gut health without real medical testing. Before trying any dramatically different diet I would recommend at least a few things. First, get a full comprehensive metabolic blood panel along with a glucose tolerance test. These tend to run very cheap. I get one every year and generally the doctors are
happy to order one for me. Additionally, I would mention to your doctor you believe you have a gluten intolerance and request a GI workup. You'll need a referral to a gastroenterologist (and this might be a little more pricey) but they can give you the necessary tests to assess bowel motility, GI inflammation, and associated gluten intolerance. Do not assume you have one of these even though it's en vogue to assume so.
I would always encourage people to not eat like shit. However, before doing anything dramatic get the proper testing done.
As a last note, insulin is used to control blood sugar.
Insulin is anabolic. Anabolism implies fat burning. In fact, in bodybuilding circles insulin-loading is one of the many ways they get huge. What you are likely correlating here is
insulin tolerance which is associated with fat gain because of your cells inability to be told to uptake glucose) the purpose of insulin. Fasted cardio is effective not due to insulin but because your body will preferentially burn circulating glucose before it burns glycogen. To entire a fat-loss state you need to be in a state where your body can be "convinced" it needs to begin converting triglycerides into muscle-food. In light of this last point, I would advise you also ask your doctor for a nutritionist, and not take advice from just any old book you read.