posted 17th Aug
In very general terms, it's either really.
You need a 1000 calorie a day deficit to lose 2lbs of weight a week. Yes, this is highly simplified, but a good way to view it. A lb of fat it 3500 calories, so you need to have a 3500 calorie deficit in order to lose a lb. That would be a 500 calorie a day deficit (500x7).
A deficit can be achieved by either increasing activity, or decreasing food. Don't decrease your food too much or you screw with your metabolism though, because your body needs a certain number of calories to function.
You can look up a few places online where they give you (based on activity, weight, height, age, and sex) the number of calories your body needs a day if you do NOTHING. Then add to that exercise, and subtract what you eat from that. A 1000 calorie deficit should net you about a 2lb loss a week.
There are of course other issues, like bloating, hormones, muscle development, that can alter that a bit, but it's a good base understanding.