What is Leptin?
Leptin is a hormone released by fat cells that helps regulate hunger. And it may hold the key to why a low carb / paleo diet works for so many people.
Success on a low carb / paleo diet is often attributed to “never feeling hungry”, an effect not seen on other diets. People point to the satiating aspects of fat or protein in eliminating hunger, but dieters may be suffering from a rarely diagnosed condition called leptin resistance that is corrected by the low carb diet.
Leptin circulates through the bloodstream in an amount directly proportional to the amount of fat you have. In theory, the more leptin you have circulating the less you will eat, because it signals that you have enough stored energy for all your metabolic processes. When leptin levels dip, it signals the brain that you are hungry.
So, that means fat people should never be hungry, right? Not so fast, grasshopper.
Resistance is Futile
Most low carbers are familiar with the concept of insulin resistance in those with type two diabetes and metabolic syndrome. In a healthy individual, insulin signals the cells that glucose is available, and the cells respond and allow the glucose to enter the cell (if they need the energy). Insulin resistance is a condition where the cells become resistant to the effects of insulin, requiring more and more insulin to deal with blood sugar levels. If a regular cell opens the door to a gentle knock, the insulin resistant cells respond only to ferocious pounding on the door with a battering-ram’s worth of insulin. The pancreas, which produces insulin, cannot keep up with the demand for more and more insulin, and dangerously high levels of blood glucose result.
A similar thing happens with leptin resistance, but through a different mechanism. There’s no shortage of leptin in an otherwise healthy obese person, and the fat cells never grow tired of producing it. But the circulating leptin is blocked and cannot turn off the hunger signal. The fat person remains hungry. And hungry people eat.
What Causes Leptin Resistance?
Some have theorized that dietary fat and blood glucose levels interfere with leptin. While there is a link between leptin resistance and the levels of fat circulating in the blood (triglycerides), eating dietary fat doesn’t seem to have an effect. Recent evidence showing a diet high in fructose contributes to leptin resistance adds to the growing body of evidence against high levels of fructose in the diet. The amount of fat in the diet did not matter; leptin resistance peaked with the high fructose diet, and reversed itself to normal levels when the rats ate a sugar free diet, no matter how much fat they had. Lucky rats.
We know that leptin signals our brain that enough energy is present, and the body does not need any more food. Leptin is able to cross the “blood brain barrier” (BBB) to do this. The BBB is a protective system of small capillaries that protects the brain from most chemicals but allows the important ones through. It works like a filter. So what causes the curious case of leptin resistance, where this essential hormone is blocked by the BBB? As Dr. Mike Eades explains:
Research done a couple of years ago in St. Louis and in Japan pinpointed the problem. Triglycerides – fat circulating in the blood – interrupts the passage of leptin across the BBB. If trigylcerides are high, which they are in most obese people, then, basically, they block the movement of leptin into the brain. So, leptin levels are elevated in the blood, and triglycerides keep the leptin from getting to where it needs to get to shut off hunger.
Controlling trigylceride levels can reverse leptin resistance. In my own experience, hunger evaporated on my low carb diet as my triglycerides fell from 344 to 105. Before that, I was often hungry, even after eating past the feeling of fullness and often to discomfort. On my low fat diet 15 years before, I was miserable because I was always hungry. But that, as they say, is a personal testimony and not a scientific finding. Too bad I’m not a rat.
The easiest way for most people to lower triglyceride levels is to adopt a very low carb diet (less than 50 grams of carbohydrate per day), then transition to a moderate carb diet devoid of most grains. Niacin and fish oil have also proven to be effective in many people, even those with genetic reasons for high triglycerides (familial hypertriglyceridemia). I combine all three approaches, and have found the eliminating any one of those results in my triglycerides rising again. Management of triglycerides in this way is done in concert with a physician and blood tests. Those with chronic health problems should check with their doctors first, of course, especially those with reduced liver or kidney function, or those suffering from conditions such as gout that require specific diets.
Humans are adapted to eat a certain diet, and in terms of adaptation, the modern agricultural era is a blip on the radar screen. We simply haven’t had time to adapt to large quantities of grain and other carbohydrates in our diets. The inexpensive access to readily available carbohydrates is new, barely 10,000 years old, and our biological machinery is not able to handle it. That’s the philosophical framework under girding the modern low carb / paleo diet movement. The rise of leptin resistance is just one more metabolic condition that supports the effectiveness of a low carb / paleo lifestyle.