Have health coaches:m/weight loss programs helped you?

I met up with a health coach today. We plan to do my full BMI and get a plan going, calorie goal, nutrition plan, and a workout plan going. With losing weight in the past Ive literally had to only eat 800-900 calories a day to actually lose weight, and my health coach wants me to up that calorie intake by a lot, like more around 1700 a day. And while I do understand the reasoning- Im terribly scared of gaining a lot of weight eating that much a day. Did upping your calories and doing things the "right" way actually work with you? Did having a health coach help you lose weight and reach your fitness goals? Im really hoping this helps me, but I can't help but fear it may cause more harm than good :(