Hi, If you have a no carb meal, you wouldn't need to take insulin with it. I was also told to always have carbs with a meal so that you can inject when I was diagnosed 8 years ago, it also depends what insulin you are on. What do you use?
Be careful though because some foods that I would consider low carb are not actually zero carb, for example if you have an omlette with salad, any dressing or sauce and things like sweetcorn do contain a small amount of carbs. Since I am on a pump, I would take a tiny amount to cover things like that, but a lot of people wouldn't bother.