Like most hormones, leptin has effects nearly everywhere in the body. In skeletal muscle, it’s involved in promoting fat oxidation. It impacts on fat cell metabolism directly, liver metabolism, is involved in immune system function (possibly why dieters get sick when they get very lean), and more recent research is suggesting effects on brain function, neurogenesis, breathing and several other functions.
I hope you’ve been following this series since the first part as this is the ninth in the series to date. To summarize what we’ve been discussing up to this point; Part 1 was focused on creating a caloric deficit, and the methods to use in order to accomplish that. Part 2 explained how to estimate the starting point of the diet regarding calories, in order to create a deficit. Part 3 was about the value of protein, and the method of calculating how much to include in the diet under the established caloric parameters, so that fat loss can begin. Part 4 dealt with essential fatty acids and other dietary fats, and how much we need to include in our diet plan. Part 5 was spent discussing how many carbohydrates are needed in our diet. Part 6 was about insulin sensitivity and resistance, and how that affects our macro nutrient needs. Part 7 offered a couple of different ways to structure the diet depending on insulin sensitivity/resistance. Part 8 was and introduction to this article and the leptin/insulin relationship. If you missed any of the articles please start the series at the beginning. Starting part way through defeats the purpose of this process. The point of this series is to educate so that you know what to do, and why. Short-cutting the learning process is not the way to be successful at anything, and fat loss is no exception.
Back to the subject at hand – leptin. Of some interest, leptin levels are crucially involved in both puberty and fertility. It’s well known that a certain level of body fat is required for puberty to develop, and achieving critical levels of leptin appears to play a role in allowing puberty to begin. It is believed that some of the reason children now hit puberty sooner is because of increasing childhood obesity.
Leptin is a key factor in regulating fertility. It lets the body and brain know that it’s well fed enough to spend calories on things like reproduction, and making babies. This at least partly explains why dieters with very low levels of body fat lose both sex drive, and the ability to sexually function. Loss of menstrual cycle is a well-known effect of dieting and intensive training, and while it was always thought to be related to body fat levels, it appears that energy availability is factor. When the body senses that energy availability is insufficient, it shuts down what are unnecessary such as reproduction.
When it was originally discovered, leptin was originally conceived as a fat regulation hormone, it was thought that leptin could act to prevent weight gain. As obese individuals invariably have high levels of leptin, raising levels in those folks does little to generate weight loss. For that reason using leptin as a treatment for weight loss has not been effective. Early ideas about leptin were incorrect. Rather than acting as a fat loss hormone, leptin appears to act as more of an anti-starvation hormone. Leptin doesn’t act to prevent weight gain, it acts to keep you from starving to death. The body doesn’t defend against weight gain very well, it defends against weight loss.
Research has found that the drop in leptin is a key aspect triggering the effects of starvation in humans. Several studies had individuals diet before replacing leptin to pre-diet levels. This raised metabolic rate, normalized thyroid, and increased fat loss. While trying to raise leptin in overweight individuals is pretty much a bust, preventing leptin from dropping on a diet is where increased fat loss is seen.
Now you know basically what leptin does in the body. It signals the brain regarding energy stores, and appears to act primarily as an anti-starvation hormone. Next time I’ll look further into what leptin does that directly affects fat loss, like impacting our appetite, and then also how to go about dealing with this on a fat loss diet.