I Have A Strong Family Hx Of CAD. Most Of

I have a strong family hx of CAD. Most of my family has died at the age of 55 or less. I recently turned 52 and had my physical. My Dr. Said my lipids are WNL and my colonoscopy was normal but I am over weight. I am 5'6" and weigh about 225. I really want to loos about 40 pounds and I know I should do it slow with exercise as a key element. should I start slow with a 2,000 calorie diet and decrease as I loose weight or should I start with a 1850 calorie diet from the get go?