No matter how much your waistline or your scale-weight has changed over the years, your number of fat cells has not changed since you finished puberty.* Think of fat cells as balloons - it's not how many you have that makes you look fat, but how full they are. Your body-fat remains constant when the number of calories you consume is the same as the number of calories you burn; it's called energy balance. When you consume more calories than you burn, the extra calories are stored as body-fat in your fat cells, and the fat cells expand to accommodate the increased volume. When you consume fewer calories than you burn, your body calls upon your stored fat content for the energy it needs to make up the difference between the calories you are consuming and the calories that are needed to fuel your activities. When your body calls upon its stored fat, the remaining fat in the fat cells becomes less than before and the size of the fat cells decreases. It's like inflating or deflating balloons.
It's really that simple. It gets complicated when people get bad information from infomercials, or from myriad sources citing "scientific data" revealing "magic secrets" about weight loss.
If you have a weight problem, you have probably had it for a while. Ask yourself a few simple questions:
1. How many diets have I been on?
2. How many pounds have I lost on each diet?
3. Do I weigh the same or more now than I did before those diets?
4. Has my doctor told me that I should lose weight?
5. If the "magic diet" really works, why didn't my doctor tell me about it?
If you're like most people with a weight problem, you have tried many fad diets, lost a lot of weight, and weigh the same or more now as you ever have.
By way of contradiction to what I have just said about your number of fat cells not increasing, it is possible to gain new fat cells. But this only occurs in cases of serious obesity, when very obese people continue gaining weight beyond the capacity of existing fat cells to store new fat. Also, increases in the number of fat cells generally occurs in the lower (femoral) body, whereas gains in abdominal fat is much more likely to be stored in existing fat cells.
But, again, new fat cell creation is not why the vast majority of overweight people are fat. It remains for most of us that we become fat when our existing fat cells store excess fat.
The signifigance of filled-up existing fat cells versus filled-up existing fat cells and new fat cell creation is that the more fat cells you have, the greater your capacity to store fat, and the more filled-up fat cells you have, the greater is the volume of your body-fat , and the harder it becomes to lose it.