I'm non-IR, too, but I had complicated food side effects that no one could understand because there were no lab results etc. that explained them, but I've done fabulously with the Metformin. My only GI type issues are mostly related to no longer having a gallbladder, but I can say that if you continue to eat carbs, you are far more likely to have the gastro effects of Metformin. When I was eating a decent number of carbs, I have to carb load to balance the effects.

Today is day 9 of me going LCHF (low carb high fat) at the recommendation of my endocrinologist for my PCOS and hypothyroidism. I had few days of adjustment/flares, but my body is adjusting very well to the system change (burning fat for fuel as our bodies are meant to do rather than carbs, which I relate to putting leaded gasoline in an unleaded engine - it will work, but inefficiently, and likely will damage the system along the way...). For me, the short term misery and bathroom hell while my system adjusts was worth the long term changes I'm gaining (mental clarity, more energy, no fog, better sleep, no cravings, etc.)...

I would check into research and see if the long term benefits might outweigh the short term adjustment misery. You know how they say it gets worse before it gets better? Very true here. I haven't had any of the heartburn issues I suffered even two to three days before starting this since I started. I can eat dinner, drink water or broth until my stomach seems as full as it can get, and immediately go to bed without any bile issues, no stomach acid in the throat, no heartburn, and no sprinting to the bathroom with 15 seconds of notice. I like the changes I'm seeing, but I don't know if getting your body back to it's intended function would help your conditions or not.

I am on metformin and eating about the same percentages as you do. I have absolutely no side effects on metformin ER ... only once, when I endulged in a way too fatty and too much dinner. Taught me a lesson, that night ...

How would one know if they are insulin resistant? Is there a test to take?
My obgyn doctor prescribed Metformin to me about a year ago (maybe longer). I take 850mg daily. Mind you, I am SUPPOSE to take the tablet twice a day....I dont. I just saw my obgyn yesterday, and he told me that I truly needed to take it twice a day for it's full benefits. He said the once a day method helps with lowering blood sugar (though I have not been diagnosed with diabetes but it runs in my family) but may not help with all my PCOS concerns.
In 2013 I had lots of women's health issues...namely I had extremely long and heavy periods. I was diagnosed with PCOS when I was 17. Im 29 now. throughout the years I have struggled with a variety of women's health issues...irregular periods, ovarian cysts that burst causing pain, and most recently in 2013 I was in and out of the obgyn office because of extremely long and heavy periods. I had to have a low dose depo shot to stop my period, followed by a D&C to clean out my uterus because of excessive lining build up. That procedure happened September 2013. Thankfully, since January 2014 I have had a regular monthly periods. I think the metformin has helped. I have never been pregnant, but I haven't really tried to get pregnant either. Now that I am newly married, I hope to lose some weight 50+lbs and try. FINGERS CROSSED.

I take the Metformin extended release also but I take mine twice a day. It helps my tummy a lot! My doctor explained that the ER still is mostly out of your system in 12 hours, give or take, and that taking it twice a day means its in your body for a whole 24 hours. So no ups and downs and that helps you not have as much tummy problems.

But food will set me off if I eat too many carbs or eat any carbs without a decent amount of fat to slow the digestion.

You will have to try to find what works best for you thru trial and error. We're all special snowflakes, so to speak, and what works for me might not work as well for you.

You'll have far less side effects if you keep your carbs low from the beginning, which I totally did not do! Good luck.