Leptin is a hormone that occurs naturally in our bodies and is thought to regulate metabolism and fat burning. It is created in the fat cells and used, for the most part, by the hypothalamus, a part of the brain that is tied to the endocrine system. The hypothalamus regulates sleep, hunger, body temperature, and thirst.
Leptin reduces appetite and operates on both an immediate and long-term basis. In the near-term, leptin tells us that we are full and that we should not eat any more food. In the long-term, leptin tells us that we have enough fat stored already and do not need to continue eating to build more storage. Leptin also regulates ideal body weight by manipulating other chemicals in our bodies. When our bodies secrete substances that would otherwise cause us to feel hungry, leptin overrides the message. Leptin also causes our bodies to increase production of naturally occurring appetite suppressants.
Based on the science of leptin, our bodies should be incapable of becoming overweight even in the absence of calorie counting and aerobic exercise. And this was probably true, back when we lived in caves. However, this is no longer the case. Unfortunately, many people who eat the wrong kinds of foods can eventually develop leptin resistance. This is because these foods create inflammation in the body tissues and the anti-histamine chemicals we produce as a result of the inflammation interfere with leptin functioning. Over time, leptin resistance will make the body ignore the notion of an “ideal” weight, allowing unnecessary hunger signals and storing excess energy as fat whenever it becomes available.
Research has established that the types of foods we eat are largely responsible for leptin resistance. For example fructose, a naturally occurring sugar found in fruit, has been shown to both reduce the efficiency of leptin receptors in the hypothalamus and prevent leptin from reaching the brain altogether. Further, grains have been shown to physically block leptin receptors so that leptin cannot reach them.
In recent years, several “fat resistance” diet books have been published to help people reverse leptin resistance and jump start metabolic fat burning. These diets focus heavily on eliminating from the diet all foods that contribute to the body’s inflammatory response (and, by extension, leptin resistance) and adding foods that help reduce inflammation, such as omega-3 fatty acids, fruits, vegetables and lean proteins.