Sounds pretty innocuous, harmless. Easy to ignore.
Except that, if you’re trying to lose weight, manage weight or change your physique, you’d be wise not to ignore leptin.
So what is leptin? I’m glad you asked! Of course, I was going to tell you anyway…
Leptin is a hormone. It’s name comes from the Greek leptos, or thin.
It’s made in the small intestine by adipose cells and enterocytes, cells that line the inner surface of the small intestine.
Leptin is often called the “obesity hormone” or “fat hormone.” But maybe it’s just big-boned, try not to be cruel. Sorry, the bad jokes are just laying around…
It’s also been referred to as the “energy expenditure hormone” and the “satiety hormone” as well as the “starvation hormone.”
Hmm, that seems like a wide disparity of names for one hormone.
How did it get so many nicknames?
In truth, it probably shouldn’t have some of those. That said, they all have a kernel of truth to them.
In case you haven’t figured it out yet, leptin is heavily involved in metabolism, particularly with regard to fat storage.
But it has other functions, too.
Leptin is believed to have a role in bone metabolism, neurocognition, brain plasticity and immune function. In fact, low circulating plasma leptin has been connected to the cognitive changes seen in anorexia, depression and Alzheimer’s Disease.
But it’s largest scale and arguably most important function is metabolic in nature.
According to Dr. Robert Lustig, MD, author of the book Fat Chance: Beating the Odds against Sugar, Processed Food, Obesity, and Disease, and a professor of pediatrics in the Division of Endocrinology at the University of San Francisco, starvation hormone is most accurate.
He says, “leptin is the way your fat cells tell your brain that your energy thermostat is set right.”
“Leptin tells your brain that you have enough energy stored in your fat cells to engage in normal, relatively expensive metabolic processes.”
“In other words, when leptin levels are at a certain threshold — for each person, it’s probably genetically set — when your leptin level is above that threshold, your brain senses that you have energy sufficiency, which means you can burn energy at a normal rate, eat food at a normal amount, engage in exercise at a normal rate, and you can engage in expensive processes, like puberty and pregnancy”.
So leptin signals the brain when you have enough fat stored. It tells the brain to go ahead and do all the stuff you want to do.
It sends this signal to a part of the brain called the arcuate nucleus of the hypothalamus. The hypothalamus is a part of the midbrain and is just below the thalamus.
Generally speaking, higher levels of blood leptin are associated with inhibited hunger. Your leptin levels are higher between midnight and early morning, probably to allow you to sleep undisturbed by hunger.
Lower leptin levels have also been observed in sleep-deprived people. This may be related to signaling designed to increase energy levels via food intake to counter the effects of sleep deprivation.
Exercise reduces leptin levels. Again, this makes sense since the brain and body would need to replace the energy expended during exercise.
Levels of leptin rise during periods of emotional stress. This is likely tied to the primitive fight-or-flight response, which is driven by a primitive part of the brain called the amygdala.
So if leptin acts like a thermostat, call it a “fat-o-stat,” why do otherwise healthy people gain weight?
The problem could be leptin resistance.
It’s similar to insulin resistance, wherein the body produces large amounts of insulin, but the body ignores it.
Lustig says, “In leptin resistance, your leptin is high, which means you’re fat, but your brain can’t see it. In other words, your brain is starved, while your body is obese. And that’s what obesity is: it’s brain starvation.”
To make matters worse, leptin is connected to your reward system via dopamine, the reward hormone. When leptin is low, food is even more rewarding.
The same problem exists when you’re leptin resistant.
Leptin resistance is now believed to be one of the main biological contributors to obesity.
The brain can’t see the leptin. It then thinks your body is starving. The brain then changes it’s approach to food, metabolism and fat storage by making you eat more and reduce caloric output. It’s a kind of fat-gaining perfect storm.
In this scenario, eating more and exercising less is a symptom of the problem, rather than the cause.
Even if you manage to lose weight, your leptin levels fall. Your brain’s leptin resistance? Probably not so much.
Leptin falls, hunger goes up, appetite increases and the desire to work out goes away. To make matters worse, your resting metabolic rate, or RMR, falls, too.
That’s the number of calories you burn at rest.
It’s your brain not getting the leptin memo and going to work to get you to regain that body fat!
By now you’re saying, this sucks! I don’t blame you!
What causes leptin resistance and how do I avoid it or reverse it?
One question at a time, please!
We’re not absolutely sure of all the causes of leptin resistance, but we know a few.
High leptin – When you have elevated leptin levels, this seems to cause, or at least contribute to, leptin resistance.
Free fatty acids – High levels of free fatty acids in the blood seems to increase fat metabolites in your brain and mess with leptin signaling.
Inflammation – This seems to be pretty well documented. Inflammatory signaling in the hypothalamus seems to drive leptin resistance. Science has been able to show this in both humans and animals.
Obesity makes all of these worse, meaning it may be harder to break out of the vicious cycle of weight gain and lower your leptin resistance.
All is not lost. Look in the mirror. If you have high body fat, especially belly fat, leptin resistance is almost certainly a problem for you.
While there is no absolutely certain way to reverse it, here are some things that seem to help;
Exercise – This seems to help reverse leptin resistance.
Sleep – Disrupted or poor sleep are associated with leptin problems.
Avoid processed foods – This is a great idea anyway, but highly processed foods seem to compromise the integrity of your gut and increase inflammation.
Eat protein – Eating enough protein supports weight loss. This may be the result of an improvement in leptin sensitivity.
Eat soluble fiber – This improves gut health and protects against obesity.
Lower your triglycerides – High triglycerides can block transport of leptin to the brain. Lower your carb intake, especially starchy carbs like breads and pastas and you may be helping yourself in the leptin department.
So if you’re struggling to lose weight or caught up in a yo-yo cycle, it may not be your fault. You may have an issue with leptin resistance.
The most likely culprit is always diet and exercise. But if you’ve got those pretty well nailed down or are having problems with cravings and keeping the weight off, leptin may be a problem.
I hope this has been helpful.
Keep the faith and keep after it!