The ketogenic diet relies on cutting carbohydrates to a low level, especially the easily absorbed sugar carbs. Eating elevated amounts of dietary carbohydrates helps keep your body in a mode where it's always ready to store the excess not burned off in exercise or normal metabolic processes as fat.

The body tries to keep the amount of body fat it stores at a steady level, maintaining “homeostatis”. That means your body becomes used to an amount of body fat and if your diet and activities start to consume that fat, your body will try to convert & store some easily available sugar stores from the blood as fat. Likewise, if your activity levels and metabolism are lower than normal, it takes a little while for the body to raise the set point and start storing fat. If you're losing weight and you hit a plateau where it seems like you can't lose any more. You may have reached where your body fat set point is. What does this mean when you're using a low-carb/high fat diet to lose weight?

We care because this has some very important implications for human obesity. With such a powerful system in place to keep body fat mass in a narrow range, a major departure from that range implies that the system isn’t functioning correctly. In other words, obesity has to result from a defect in the system that regulates body fat, because a properly functioning system would not have allowed that degree of fat gain in the first place.

So yes, we are gaining weight because we eat too many calories relative to energy expended. But why are we eating too many calories? Because the system that should be defending a low fat mass is now defending a high fat mass. Therefore, the solution is not simply to restrict calories, or burn more calories through exercise, but to try to “reset” the system that decides what fat mass to defend. Restricting calories isn’t necessarily a good solution because the body will attempt to defend its setpoint, whether high or low, by increasing hunger and decreasing its metabolic rate. That’s why low-calorie diets, and most diets in general, typically fail in the long term. It’s miserable to fight hunger every day.

But when you maintain a state of ketosis by carefully avoiding sugary carbs and trying to permit only fat-calories, as much as possible, this helps to get past your body fat setpoint as you lose weight. Denying your body the easy-to-store spare carbs means it is less able to maintain the setpoint for long and you'll soon be dropping pounds once again.

Hitting that plateau can be frustrating, but stick to the low-carb diet and make sure to burn off excess carbs with exercise to stay in ketosis.

Check out Stephan's article over at WholeHealthSource for more on the body fat setpoint.