Let’s first preface this discussion with some basic math stuffs. Your body is like a battery, excuse the sorry analogy. To do work it must intake a sufficient level of calories to convert into usable energy, which in our bodies is ATP or adenosine triphosphate. At the end of the day, excess levels of ATP are stored as either fat glycogen or other sugar substrates… or excreted. This is a gross simplification but it is sufficient for our purposes.

So let’s say you intake 4,000 calories over the course of the day but only do enough activity to burn 3,000. Well, chances are a portion of that unused energy is going to be stored as excess weight. How your body deals with this excess is specific to you, but in general, the above rule holds true. So you might ask next if there is a baseline as to how much you should consume per day. Well there is and it is called your basal metabolic rate. It is the measure of how many calories your body requires to be able to support its basic functions were you to be asleep all day. Figuring out your BMR requires rather strict testing conditions and calorimetric analysis of your breathing. For our purposes we will use a resting metabolic rate prediction or RMR. RMR is a rough estimate while BMR is precisely the number of calories your body requires while at rest.

The primary reason that most people cannot maintain a certain weight, or achieve a particular weight related goal, is because they are consuming more calories than they are using in a given day. Other factors do contribute, but this is the primary reason. The following resource provides an excellent calculator that will estimate your RMR. Use this as a baseline number of how many calories you should be consuming per day. Also, pay attention to the various levels of activity and how they require more or less calories. For example, a strenuous level of activity requires more calories per day than a sedentary level of activity. http://www.caloriesperhour.com/index_burn.php

Once there, click on “BMR & RMR Calculator“, populate the blank fields and see what it reports. If it tells you that your RMR for a light level of activity is 2,500 calories, and you are consuming 3,500, then you can assume that it is likely that if you want to drop some weight then you should lessen your caloric intake.  It is a give and take model, you want to provide as many calories as you are going to use and if you consume excess calories, expect weight gain.

For a lengthier discussion on BMR/RMR, the following is a excellent, concise read.

http://www.caloriesperhour.com/tutorial_BMR.php