PLEASE HELP!! How Many Calories Does My 485 Pound Husband Need a Day to Lose Weight?

I recently got married to an amazing man. He weighs 485 pounds and is determined to lose weight now before anything bad happens to him (God forbid). He has been on a diet that I put him on, basically eliminating all white carbs and replacing them with brown carbs, and grilled fish and chicken with salads, fruits and veggies. Problem is, he has been feeling "horrible" with low energy. I dont think I have incorporated enough calories in his diet plan, since him being 485 pounds may need more than the average person. His goal is to lose about 100 pounds. So how many calories does HE need a day in order to lose weight? Thanks so much for your anticipated help