Your weight is largely controlled by your brain's weight regulating mechanism called the "fat thermostat". The setpoint of this fat thermostat influences your appetite, your energy and your level of weight. The weight regulating mechanism plays a crucial role in the day-to-day drama of weight loss and weight gain. Once the fat level, or setpoint, has been established, your weight regulating mechanism works stubbornly to defend that level. Influence is exerted on two key functions, your appetite and your metabolism. The weight regulating mechanism will signal you to take in more food when it feels that your supply of stored energy (fat) is threatened. Likewise, it will decrease your body's metabolic rate so that you may use less energy and burn fat at a lower rate.
The kinds of food you eat affect your setpoint, your appetite, and ultimately, your weight. Intake of foods dense in fat, refined carbohydrates like sugar and white flour stimulate a vicious weight gaining cycle. Sugars and other refined carbohydrates are quickly digested and absorbed into the bloodstream. Then you feel hungry again, and the cycle continues.
The rapid absorption of sugar creates an elevation in blood sugar, which in turn causes an increase in insulin production. Insulin is an essential hormone that allows the cells of the body to take in and burn sugar from the bloodstream.
Excess insulin can actually cause increased fat storage. Most obese people have excessive insulin because their cells seem to be resistant to it and the body produces more to overcome this resistance. In the presence of excess insulin, a disproportionate share of the sugar in the bloodstream is converted to fat and deposited in the fat stores.
Also, excess insulin seems to slow the breakdown of fats for the energy needs of the the body. This triggers a signal for more frequent eating, and a preference for more sugar. You feel tired and weak and move slowly to conserve energy. When your body doesn't get enough energy, it will start breaking down muscle tissue, leaving you weaker and flabbier.
What a dilemma!
Other factors that affect weight regulation are:
Most important to remember is that you have control over most of these weight regulating influences - the type of food you eat and your activity level.