Overweight..bmi above 40 suggest deit?

It varies: A healthy well-balanced diet, 3 meals without snacks. Caloric restriction if you need to lose weight. There's no magic here. Find an eating plan you can follow the rest of your life, not a short-term diet. Check w/your registered dietitian.

Try using : MyFitnessPal it is a free app that will help you keep track of food intake, exercise, nutrition. Eat a well rounded diet in moderation. Consider working with a therapist or nutritionist as well.

Just the Basics: To lose weight insure that calories burned > calories consumed. Drink at least 8 - 8 oz glasses of water /day. Try for 8 hrs of sleep/night. Aim for at least 5 servings of vegetables & 4 of fruit per day. Use whole grains. Avoid sodas, alcohol & junk carbohydrates. Get in a good mix of aerobic & weight lifting exercises.