Couple things on IBS: Fish oil and glutamine are not only low-carb and fat-loss friendly, but also GREAT for IBS. Fish oil is anti-inflammatory, and glutamine helps repair the gut.

Iron is in beef (and I think spinach). Vitamin C is in orange peppers, and they are fairly low-carb. And there's always time-release vitamin C supps.

You can do low-carb without going into ketosis. And even if you DO go ultra-low carb, your body gets used to performing on fat after about 2-3 weeks. It's a little humiliating at first, but once you switch over to the different fuel system, you're fine. Just be sure to keep your fats up, especially fibrous fats like avocados. Fats REALLY need to be high - like, 60-70% of total cals. Otherwise, you'll really feel like crap.

Good luck! I've known quite a few people with IBS who have done really well on low-carb high-fat.