Hi all;
K9, you are right. I replied in too much a rush before dashing out for a meeting and did not get my thinking straight. Bottom line, I got myself all screwed up. I apologise.
The maths is that (assuming you were to lie in bed all day - which none of us do
) the average woman needs approximately 2000 calories intake a day (an average man needs 2500) to remain at a stable weight.
If you are taking in 500 calories therefore, you are running at a defecit of 1500 calories. Up your intake by 500 calories to 1000 and the defecit becomes 1000 calories, or 2/3 of what it was before.
As you stated, 1 pound of fat provides the body with 3500 (approx) calories of energy, so at a defecit of 1500 calories you will burn around 10500 calories extra a week, which equates to 3 pounds of fat. If you are running at a defecit of 1000 calories you will burn 7000 calories extra a week, and this equates to 2 pounds of fat.
Naturally, as your activity levels increase your bodys energy requirements increase and so your calorie defecit increases. The result is that the amount of body fat burned to meet the extra energy needs will also increase. For example if you were to do a little light exercise each day that burned off an extra 500 calories, then over a week that would be an extra 3500 calories that the body would need and so it would burn an extra pound of fat.
Also, you need to remember that this is all based on an "average" person, and no-one is average. The actual defecit that you will be running at will depend on your BMR (Basal Metabolic Rate), which is the actual number of calories that you need to take in to maintain your weight at zero activity. The heavier you are, the higher your BMR will be, and therefore the bigger your defecit will be. This is why heavier people lose weight faster - it is basic physics that says that it takes more energy to move a heavy object from A to B than it does to move a lighter object. This is why our weight losses slow down a little as we get lighter. It also explains why if you go back to eating exactly the way you did you can put the weight back on very fast because the calorie excess is much greater at your new lower BMR.
If you know your BMR and your calorie intake, you can pretty accurately predict what weight you are likely to lose in a week - though the body does throw the odd spanner into the works. For example, I had a stretch of 7 weeks of losing 3 pounds, week after week after week. Suddenly, with no explanation or reason - I changed nothing, I dropped 8 pounds. After that week I went to losing 2 pounds a week, week in week out. I still have not managed to find a scientific explanation for that oddity!!
