Leptin is a hormone that is secreted by your adipose (fat) tissue. In the most general sense, it has two main functions:
- Influence your appetite.
- Enhance your insulin sensitivity and fatty acid oxidation.
Leptin is tied to your appetite. As leptin levels increase, your appetite decreases, and vice versa. In scientific terms, it modulates energy intake by seeking to maintain an energy balance (basically, leptin plays a role in helping your body find equilibrium).
With that said, leptin strongly correlates to fat mass. The fatter you are, the more leptin you have. This may seem counterintuitive given what I just said about leptin functioning as an energy regulator. However, the leptin “system” is far more sensitive to starvation that it is to over eating. Leptin levels drop much faster when your body perceives a food shortage than they raise when your system perceives a food surplus.
During periods of energy deficit, the fall in leptin plasma levels exceeds the rate at which fat stores decrease. Reduction of the leptin signal induces several neuroendocrine responses that tend to limit weight loss, such as hunger, food-seeking behavior, and suppression of plasma thyroid hormone levels. Conversely, it is unlikely that leptin has evolved to prevent obesity when plenty of palatable foods are available because the elevated plasma leptin levels resulting from the increased adipose tissue mass do not prevent the development of obesity. In conclusion, in humans, the leptin signaling system appears to be mainly involved in maintenance of adequate energy stores for survival during periods of energy deficit. [Jequier, Eric. Leptin Signaling, Adiposity, and Energy Balance. Annals of the New York Academy of Sciences, 967: 379–388.]
It’s a simple survival mechanism that prepares your body for the next drought, or locust attack or whatever.
But once you are fatter, leptin eventually catches up and seeks to maintain your weight once again. Therefore, leptin levels are higher in fatter people, and lower in thinner people.
Now consider this. A 1997 study in the Journal of Clinical Endocrinology and Metabolism looked at the effects of fasting and fat loss on leptin levels. You want numbers? In a group of 9 obese males who lost 21.4% of their body weight, leptin levels fell 76.3% from their baseline. After 3 days of fasting, a group of 7 nonobese females lost 2.6% of their body weight. And their plasma levels plummeted by 61.9%. The study found that yes, leptin levels are primarily correlated to total adipose mass, but on going fasting reduced leptin faster than would be expected that the corresponding fat loss alone. [Weigle D., et al. Effect of Fasting, Refeeding, and Dietary Fat Restriction on Plasma Leptin Levels". 1997 Journal of Clinical Endocrinology and Metabolism. 82 (2): 561–565]
Ok, take all that in. And then realize that this is one of the main reasons your ultra low-caloried diets are doomed to fail. At a very basic level:
- You Significantly reduce calories.
- Leptin levels plummet
- You get VERY hungry.
- You overeat by a lot.
- Leptin levels reset themselves higher than they were before your ultra low calorie diet.
So leptin could very well be sabotaging your fat loss efforts. Tomorrow, I’ll show you how leptin, when in harmony with your other hormones, can help you melt fast faster than ever.
Now I’d like to hear what you think. Do you agree? Disagree?
Hit me with your comments and questions below!
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