I’m going to wash briefly over this topic to give you a basic understanding. If you want a more in-depth understanding, there’s loads of in-depth information out there on Google. Leptin is a pretty misunderstood and forgotten hormone that was only discovered in the late 90s. We’ve known about insulin, in contrast, for about 50-60 years.
The fat stores in your body aren’t static, energy bins. They are actually an active endocrine gland – they make stuff. Lots of inflammatory chemicals get made by your fat stores, especially in those with high bodyfat percentages. Crucially, they also make a hormone called leptin.
Leptin is your body’s ‘fat reporter’, and the hypothalamus in your brain responds to leptin by affecting your body’s metabolism. When your fat stores are at a good level, your metabolism stays where it is. During a famine, when you have insufficient fat stores to survive on, your brain talks to your thyroid and decreases your metabolism, and increases your appetite (via hormones like ghrelin).
However, when you’re overweight, the converse is not true. Your metabolism is not cranked up as a result of extra fat stores, because you’ve developed leptin resistance. So, your brain interprets its perceived lack of communication from leptin by slowing the metabolism and increasing the appetite.
Leptin resistance can be caused by:
- Excess overeating and excess caloric restriction (<1000 calories/day)
- Excess fructose in the diet (e.g. high-fructose corn syrup)
- Excess wheat in the diet (more on this in later articles)
While all of this may seem confusing and scary, don’t overthink it. If you’re trying to lose bodyfat, try intermittent fasting and keto for an extended period without worrying too much about leptin.