By the way, your trainer is incorrect about that anyway.
Even though Spark does account for your exercise, it's entirely possible to be under the 1200 'net' calories - eg eat 1400 do 300 in working out.
However, that's absolutely no problem.
The whole reason 1200 is often mentioned as a minimum is that, at intake levels lower than that many calories, on average, you're not likely to be getting enough vitamins and minerals. But vitamins and minerals are not depleted by exercise. You did 300 calories of exercise - better have some more selenium? No.
So once those 1200 calories have passed the lips, the vitamins and minerals in them are being absorbed by your body and it's not necessary to add more.
The energy? Well, personally I do doubt that many people need to eating so low and exercising so much that this 'net' value does drop below 1200, but it's not a major if it does. Subtracting exercise from food doesn't actually tell you anything by itself. I could give you stats for people who would maintain, gain, or lose, on exactly the same 'net' calories.
What is important is BMR + daily activity + exercise and then - food. The remainder should be a positive value, eg 1500 BMR + 300 daily activity + 300 exercise = 2100 spent, minus 1400 eaten should lead to about three quarters of a pound a week lost.
Notice that example, while it would lead to good weight loss, is sub-1200 "net" (1400 - 300).
Deb, in New Zealand