I am 45 pounds overweight. Should I track calories or fat grams?

I have heard many different opinions as to what to go by when trying to lose weight. I am about 45 pounds overweight and have finally started trying to lose some of it. Some people have told me to go by the number of calories in a product as to whether it is healthy or not and others have told me to go by fat grams. What exactly should I go by and what are some good numbers to go by?

Fat grams seem to work for a lot of folks, but you should also keep track of calories. (Read the remaining questions in the Overweight topic.) Next, take the total calories you eat per day and multiply by 30% to determine the number of calories from fat. (If you ate 1200 calories per day times 30% equals 360 fat calories.) Lastly, divide by 9 calories per gram to get the fat gram total for a day. (Divide 360 calories by 9 to get 40 fat grams.)

The only problem with this is it does not take into consideration vitamin and mineral content which calorie or fat gram content cannot determine.