I still eat quinoa and yogurt; I just try to avoid simple carbs and straight sugar. Whole wheat pasta, full grain breads, no soda, etc. My glucose levels have improved greatly since taking metformin, losing weight, and reducing my sugar intake. I still eat way too much sugar according to MFP, but it's mostly fruit, which my doctor said is ok, but you may want to check with yours if they think it's ok. If I go crazy and eat a bunch of carbs and sweets one night, my stomach definitely feels it due to the metformin. I would suggest cutting back drastically on sugar when you start metformin, it seems to mess everyone's stomachs up for a while and the sugar seems to exacerbate that, but it will go away after a couple weeks.

It kind of depends on what you like; really you should avoid anything super sugary that you are inclined to eat. For me it's cane sugar soda, candy, ice-cream, cookies, cakes, smoothies, and juice. I also try to make all my pasta dishes with whole wheat or quinoa pasta, instead of the enriched flower options. I think whole grain products are broken down slower than regular flower type products, so your body gets a steadier lower stream of carbs/sugar, rather than a sudden spike. I still eat yogurt, fruit, and the occasional portion controlled ice cream or candy and I'm fine. I would avoid the candy/ice cream upon beginning metformin though and slowly add it back if you want to and see how your digestive system reacts.