Key Takeaways

  1. Leptin is a hormone primarily produced by fat cells that’s involved in many functions in the body including regulating appetite, metabolic rate, motivation, immunity, fertility, and libido, to name a few.
  2. Low leptin levels are the root cause of most of the negative effects of dieting, including increased hunger and decreased metabolic rate and energy levels.
  3. The best way to deal with the negative effects caused by low leptin levels is to include pre-planned “diet breaks” during your cut where you increase your calories and carb intake.

The first few weeks after starting a diet are usually smooth sailing.

You aren’t that hungry, your energy levels are good, and you’re still adding weight in the gym.

Then, often at about the four to eight week mark, the gears begin to grind to a halt.

You feel more hungry before meals and less satisfied after.

Your energy levels drop and it becomes increasingly hard to add weight to your compound exercises.

And worst of all, the number on the scale moves slower and slower with every weekly weigh in.

What changed?

Why did dieting suddenly transform from a sprint into a slog?

Are you eating too much or too little? Not doing enough cardio? Not eating the right foods? Not taking the right supplements?

The answer to all of those questions lies in a hormone called leptin, which is the topic of this article.

Leptin lies at the center of the constellation of problems every dieter experiences as they lose fat—lethargy, hunger, metabolic slowdown, and even increased risk of illness.

Like anything related to weight loss, there’s a lot of misinformation, hype, and chicanery surrounding leptin.

In the past decade a new wave of Internet doctors, fitness gurus, and online influencers have seized on the significance of leptin and come up with specialized diets and supplements designed to “hack” weight loss by controlling leptin.  

They throw around enough big words and studies to make their pitch sound sciency, but like any fad diet, it’s all a bunch of smoke and mirrors.

There’s no such thing as “hacking” your metabolism, hormones, or body fat, though, and controlling leptin levels isn’t the secret to weight loss any more than controlling other hormones like insulin or testosterone is.

Now for the good news:

Understanding how this hormone works can give you a better perspective on what’s going on inside your body as you lose weight and how to make fat loss easier by making a few simple modifications to your diet.

On the plus side, though, understanding the workings of leptin allows you to make a few informed changes to your diet that make losing weight significantly easier.

Let’s start by looking at what leptin is.

What Is Leptin?

Leptin is a hormone primarily produced by fat cells that’s involved in many functions in the body including regulating appetite, metabolic rate, motivation, immunity, fertility, and libido, to name a few.

Leptin’s main job, though, is to help you maintain a healthy body weight.

It does this by keeping your brain informed as to how much energy is available in the form of body fat and calories from your diet.

When leptin levels are high, this tells your brain you have plenty of energy available in the form of stored body fat and dietary calories. The brain responds by reducing hunger and increasing metabolically expensive activities like muscle growth, sex, pregnancy, and exercise.

When leptin levels are low, though, this tells your brain your body fat stores and calorie intake are dwindling. The brain responds by increasing hunger and decreasing “spending” on the aforementioned activities.

This manifests itself in the form of lethargy, lack of motivation, and the general malaise that you feel when cutting calories.

In other words, low leptin levels are largely responsible for the negative feelings you experience when dieting.

Here’s how the process works in a nutshell:

leptin resistance

In healthy humans, this “feedback” loop works incredibly well and helps us maintain healthy levels of body fat.

We get hungry, we eat until our body tells us its full, it stores some of the food as fat and uses some for energy, we go about our day, expending energy and burning fat, our body tells us it needs more energy, we eat until full, and the cycle repeats.

In this way, our body is normally able to maintain our weight in a very narrow range, never allowing us to gain or lose too much fat.

As you can see, leptin plays a key role in the body—helping us consume enough energy to stay healthy, happy, and vibrant, while keeping us from eating so much that we become the opposite.

At this point you may be wondering, if that’s true, then how do people ever become overweight?

Why isn’t leptin keeping them from overeating?

Let’s find out.

How Does Leptin Affect Weight Loss?

To understand how leptin affects weight loss, you have to understand how leptin levels rise and fall in response to your diet and body composition.

Leptin levels in the body ebb and flow in relation to two variables:

  1. Your daily calorie intake.
  2. Your body fat levels.

When you’re eating enough calories to maintain or gain weight, fat cells secrete leptin to signal your brain that you have an ample influx of energy. As you learned a moment ago, this triggers the brain to decrease hunger and increase activity levels and other calorically costly activities.

Leptin levels closely correlate with your food intake on an hourly basis, rising as soon as five hours after eating a meal. Leptin levels are also particularly sensitive to carbohydrate-rich foods, which produce the greatest rise in leptin.

Likewise, leptin levels can also fall within a matter of days after you begin restricting calories for weight loss. For example, in one study conducted by scientists at Washington University, obese people who ate 1,000 calories per day (creating a massive calorie deficit) experienced a 26% drop in leptin levels after 10 days.

Another study conducted by scientists at the University of Chicago found that a week of undereating (70% of total daily energy expenditure) decreased leptin levels by 30 to 50%.

Leptin also helps control appetite and activity levels over the long-term, too, by keeping the brain apprised of your total body fat levels.

Despite what many people think, body fat is more than just an ugly, greasy, encumbrance. It’s the body’s best way to store energy, and it’s kept humans alive in times of famine for thousands of years.

As a result, the body evolved an elegant and resilient system for keeping careful tabs on how much body fat it has on hand at any one time.

Body fat is the main organ that creates leptin, and so when body fat levels rise, leptin levels rise in lock step.

Conversely, when body fat levels fall, leptin levels fall as well.

In this way, the brain is able to monitor how much energy it has available at any one time—in the short-term by using leptin to monitor calorie intake relative to expenditure, and in the long-term by using leptin to monitor body fat levels.

Here’s where things get interesting.

Leptin not only tells the brain what’s going on, it also acts as a kind of master regulator for many of the other hormones that are involved in fat loss, muscle gain, mood, and hunger.

For example, when leptin levels drop, this affects a number of other hormones involved in appetite, fat burning, and energy expenditure:

  • Thyroid hormone decreases, which reduces metabolic rate and fat burning
  • Neuropeptide Y and agouti-related peptide rise, which increases appetite and fat storage and decreases metabolic rate
  • Cocaine and amphetamine regulated transcript fall, which increases appetite
  • Cholecystokinin, a hormone that increases fullness, stops working as effectively, which further raises appetite
  • Ghrelin, one of the primary hormones responsible for stimulating hunger, skyrockets.

Leptin also directly increases fat burning in muscle tissue. And when leptin levels fall, this additional boost in full body fat burning dries up as well.

What’s more, low leptin levels depress immune function, which is part of why people who are dieting get sick more often than people who are eating enough calories to maintain or gain weight.

When body fat levels get low enough, there’s almost no detectable leptin in the blood, which is why it’s almost impossible not to feel hungry, tired, and lethargic when you get extremely lean (typically around 8% body fat for men and 20% for women).

When people who’ve been dieting for a while get an injection of synthetic leptin, these symptoms disappear, their metabolic rate increases, and they lose weight faster.

So, why don’t obese people just get a shot of leptin to lose weight?

It turns out scientists tried this, and it turned into a colossal failure.


How can this fat-burning, energizing, invigorating hormone not produce massive weight loss in those with the most weight to lose?

Simple: people with lots of body fat have high leptin levels—far more than lean people.

This is why injecting them with leptin doesn’t make them lose weight. They already have sky-high leptin levels, and thus jacking it up even further doesn’t produce any additional benefits.

What’s going on here?

Why are obese people driven to eat so much? Why aren’t their brains—swimming in leptin—reducing hunger and increasing the desire to exercise?

Is this a glitch in the matrix?

The hitch in this case is something known as leptin resistance.

Like insulin resistance, leptin resistance is a condition wherein the body becomes less sensitive to leptin’s signals, which wreaks havoc on the appetite and metabolism.

Scientists aren’t entirely sure why this occurs, but the fact is that overweight people have extremely high leptin levels, but their brain still believes they’re running low on energy and takes the actions mentioned earlier to increase energy intake and decrease output.

Despite being overweight, these people want to eat more and exercise less.

Now, if you’ve spent any time on the Internet reading about weight loss, you may have heard some people point to leptin resistance as proof that the “calories in vs. calories out” theory of weight loss is bunk.

Stop worrying about your calorie intake, they coo, optimize your hormones and metabolism and weight loss will take care of itself.

Nothing could be further from the truth.

The fact is leptin resistance simply helps us better understand why restricting calories is difficult and doesn’t always result in as much weight loss as we’d expect. It doesn’t change the fact that you still have to restrict calories to lose weight.

While scientists aren’t sure how or why leptin resistance occurs at the cellular level, they have a pretty clear idea of what lifestyle factors lead to leptin resistance, and thus what people can do to pull themselves out of this metabolic quagmire.

For one thing, the main factor that causes leptin resistance is simply allowing yourself to become fat in the first place. The primary source of leptin is excess body fat, and maintaining healthy body fat levels is the best way to avoid leptin resistance.

So, what should people who are already fat do to get out of this logjam?

Well, restricting calories and reducing body fat levels reduces leptin levels and improves leptin sensitivity.

This won’t be fun in the beginning, when the body is still resistant to leptin and sending out SOS signals for more calories ASAP, but this effect diminishes as leptin levels stabilize and the brain once more becomes sensitive to leptin’s effects.

If you’re in this boat, then there’s another reason to take heart that you won’t have to deal with the nuisance of leptin resistance forever.

Remember that leptin scales both in response to short-term calorie restriction and long-term fat loss.

This is why there’s normally a rapid drop in leptin right after you start a diet—in response to reduced calories—and thereafter a gradual decrease in leptin as you whittle away your fat stores.

What this means is that while the first few weeks of a new diet might be extremely difficult, an experience many obese people can relate to, it becomes easier and easier as your body finds it’s normal, healthy leptin level.

Don’t believe me?

Here are a few examples of guys who were obese who achieved a healthy body fat percentage following the Bigger Leaner Stronger program who’ve stayed lean ever since, without steroids, dangerous fat loss drugs, or surgery:

caleb h before after

dakota before after

And here are a few examples of women who’ve achieved the same following the Thinner Leaner Stronger program:

alice before after

tina before after

These people are testaments to the fact that as long as you’re willing to stick your diet out for a few months, you can achieve and maintain a healthy, attractive physique even if you’re currently overweight and wrestling with leptin resistance.

In other words, if you lose fat, keep it off, and maintain the right habits, you can at least partially reprogram your brain to maintain a lower body fat percentage, or what researchers call your “set point.”

You can learn more about that concept in this article:

How to Change Your Body Weight Set Point

Aside from losing weight, there are two other potential ways to improve leptin sensitivity.

First, it’s possible that eating a diet of minimally processed, satiating, bland foods may help dodge the normal rise in hunger that follows from crashing leptin levels. Basically, a plant-based, high-protein bodybuilder style diet.

For example, several studies have shown that eating more simple, bland, foods can help obese people lose massive amounts of weight in short order without experiencing hunger.

Whether this is because this kind of diet improved leptin sensitivity or simply reduced hunger through other means, this diet produced significant weight loss with almost none of the discomfort normally associated with low leptin levels.

Second, there’s also indirect evidence that exercise may improve leptin sensitivity. Endurance athletes—who tend to exercise more than anyone—generally have lower leptin levels than you’d expect based on their low levels of body fat, and don’t generally suffer from intractable hunger or other symptoms of low leptin.

It’s possible this is because their exercise regimen makes their bodies more sensitive to leptin, thus requiring less to get the benefits.

Even if exercise doesn’t improve leptin sensitivity, there’s strong evidence that it helps “fine tune” your appetite so that you’re more satisfied from meals and less likely to overeat (which is basically what leptin does).

In other words, the three best ways we currently know how to improve leptin sensitivity are to lose weight, eat a healthy, minimally processed, whole-foods diet, and exercise.

How Can You Raise Leptin Levels for Easier Weight Loss?

If you’re overweight or even obese (you have a BMI over 30), then you don’t need to worry about raising leptin levels.

Focus on losing weight, eating healthy, and exercising, and your body fat and leptin levels will settle into a new, healthy, sustainable range.

What if you’re pushing the lower limits of leanness, though?

What if you’re a man looking to dip under 10% body fat or a woman looking to slim down to less than 20% body fat?

This is when the low-leptin gremlins come out to play, and why getting #shredded is so damn difficult.

Once your body fat falls below these points—10 to 12% for men and 20 to 22% for women—leptin levels bottom out, dropping to almost nothing in many cases.

This leads to unyielding hunger, constant lethargy, weak workouts, and frayed nerves. All too often, this period is punctuated by a blow-out binge that results in gaining back much of the fat that was lost and then some.

What to do about this problem?

Well, the first step is to simply acknowledge that this period isn’t going to be fun. You aren’t going to feel like yourself most of the time. Your workouts are going to feel significantly harder than normal. You’ll probably feel tired, unglued, and grouchy much of the time.

Such is life when in a prolonged calorie deficit.

Understanding and accepting that reality is going to go a long way in helping you cope with the effects of low leptin levels.

Keep in mind that if you can stick it out till the end, you’ll feel like a new person when you switch back to maintenance calories.

The second step is to take planned breaks from your diet to periodically raise leptin levels. You can think of these diet breaks as pushing your head above water to take a breath before diving back into the depths of low-calorie dieting.

Over the long-term, leptin levels are dictated by your body fat levels, and there’s nothing you can do to increase your chronic leptin levels except gain body fat.

In the short-term, though, leptin levels are largely dictated by your calorie intake, specifically, your carbohydrate intake.

Overfeeding on fat has no effect on leptin levels, whereas eating carbs causes a significant spike in leptin levels that lasts for as long as you keep feeding your body plenty of carbs. It’s unclear what effect protein overfeeding has on leptin levels, but it’s likely insignificant.

The closest thing to a “hack” for your metabolism is raise your calorie intake to maintenance for several days by eating more carbs. This temporarily raises leptin levels, which partially reverses some of the mental and physical side effects of dieting.

This strategy also replenishes glycogen levels, which results in better workout performance, and gives you an opportunity to enjoy more food for a few days.

You may be wondering if following a high-carb diet while staying in a deficit can “trick” your body into keeping leptin artificially elevated, but that’s not the case. Carbs only cause a significant boost in leptin levels if you’re eating as many or more calories than you burn.

While many people balk at the idea of taking a break from their diet and slowing down their progress, research shows this is probably more efficient in the long run.

A salient example of this comes from a study conducted by scientists at the University of Tasmania.

The scientists randomly split 51 overweight men into two groups:

  1. Group one followed a fat loss diet every day for 16 weeks.
  2. Group two followed a fat loss diet for two weeks, increased their calories to maintenance for two weeks, and repeated this process until they had spent a total of 16 weeks following the fat loss diet.

Aside from this change, both groups followed the same diet, which involved a 33% calorie deficit.

In other words, both groups spent the same amount of time in a calorie deficit (16 weeks), but one bit the bullet and did it all in one fell swoop, and the other took a two week break after every two-week stint of dieting.

The results?

The group that took planned diet breaks every two weeks lost 31 pounds, whereas the group that didn’t take breaks only lost 18 pounds.

Both groups only lost about three pounds of lean mass (most of which was likely glycogen), but the group that took diet breaks experienced half as much of a drop in metabolic rate as the group that didn’t take diet breaks.

Another review study by a scientist at the University of Illinois supported these findings when they concluded that taking diet breaks is generally more effective for maintaining muscle mass while losing fat than continuous dieting.

You can read more about this diet break study here:

Research Review: Can “Cheating” on Your Diet Help You Lose Fat Faster?

There are probably two reasons the people in this study who took diet breaks lost more fat than those who didn’t:

  1. It was easier for them to stick to the diet. Chances are good many of the people in group one didn’t stick to their 33% calorie deficit every day of the study, or they would have lost more weight.
  2. The group that took diet breaks enjoyed a slight boost in leptin levels and metabolic rate, which helped them burn more calories and lose more weight.

Admittedly, the first point is probably more significant than the second, but that doesn’t change the fact that taking diet breaks did help improve fat loss on the whole.

You probably don’t need to take as much time off as these people did, though. A few days at maintenance every few weeks is likely all you need to get the benefits of a diet break without unnecessarily prolonging your cut.

It’s also not a good idea to take diet breaks much shorter than this, though.

Although many diet gurus recommend taking a one-day per week “cheat day” to raise leptin levels, this strategy is a bad idea for a few reasons:

1. While a single high-carb meal or high-carb day will raise leptin levels, this doesn’t keep leptin levels elevated long enough to reverse the negative effects of dieting.

You see, it takes several days for your brain to recognize the increase in leptin and “trust” that your body is no longer dieting, and then to raise metabolic rate and decrease hunger.

It’s possible that it may take as long as a week or two of eating at maintenance to increase leptin levels back to where they’d normally be if you weren’t dieting (although several days is enough to produce noticeable benefits).

2. Most “cheat days” involve binging on lots of highly palatable, high-calorie, high-fat foods, which is one of the best ways to sabotage your long-term fat loss success.

No, you won’t get fat by binging for a single day, but overeating high-fat foods does little or nothing to raise leptin levels. Many people, particularly those who’ve been dieting a while, can also eat enough in a single day to wipe out most of the progress from the previous week of dieting.

In the best case scenario, this strategy just makes it significantly harder to switch back to your diet when the binge is over.

While some people swear by their weekly uninhibited binges, one for one, the people I’ve met who followed this strategy later regretted it.

Most found that themselves caught in a vicious cycle of crash dieting throughout the week, binging on as many foods as they could “get away” with on the weekend, and then repeating the cycle anew.

Not only does this hinder your fat loss efforts and negatively affect your social life, it also can lead to the dreaded “skinny fat” look if repeated for long enough.

It’s okay to cheat on your diet from time to time, but you need to do it intelligently. Check out this article to learn how:

Do You Make These 5 Cheat Meal Mistakes?

With that word of warning out of the way, how should you set up a diet break?

Here’s what I recommend:

  1. Increase your calories to maintenance for two to three days, depending on how you feel. If you feel worn down, tired, and hungry, do three days. If you feel okay but ready for a break, do two days. Use this calculator to figure out what your maintenance calories should be on these days.

  2. Keep your protein and fat intake the same as they are on your low-calorie days, and raise your calories in the form of carbs. This means focusing predominantly on high-carb, low-protein and low-fat foods like fruit, rice, potatoes, pasta, oats, and bread. This usually works out to getting at least 50% of your calories from carbs.

  3. Include carbs at every meal throughout the day (or at least in the morning and evening) so that you’re sending a prolonged signal to the brain to raise leptin levels.

  4. Keep everything else about your diet the same—meal frequency, food choices, and so forth. This makes it much easier to transition back to your low-calorie diet afterward.

  5. If you wish, include one or two treats that you’ve been craving, but make sure you keep the portions small and more or less stick to your regular protein and fat macros.

Repeat this process once every month or so if you’re above 15% (men) or 25% (women) body fat, and once every one or two weeks as you dip below 10% (men) or 20% (women).

The Bottom Line on Leptin


leptin resistance diet

No matter what you do, dieting is always going to be an unpleasant experience at some point or another.

That’s the price you pay for getting lean.

Many of the negative effects of dieting, including lethargy, hunger, and slowed weight loss, are due to low levels of leptin.

Leptin is a hormone primarily produced by fat cells that’s involved in many functions in the body including regulating appetite, metabolic rate, motivation, immunity, fertility, and libido, to name a few.

Leptin’s main job is to help you maintain a healthy body weight, and it does this by telling the brain how much total energy the body has available in the form of calories from food and body fat.

When leptin levels rise, hunger drops and metabolic rate, motivation to exercise, and mood improve.

When leptin levels drop, as happens when you restrict calories for fat loss, hunger rises and metabolic rate, motivation to exercise, and mood decrease.

Ironically, obese people have higher leptin levels than lean people. Due to a phenomenon known as leptin resistance, their brains perceive a shortage of calories in spite of high leptin levels, and increase hunger and decrease metabolic rate as a result.

The single best way to prevent leptin resistance is to not become overweight in the first place. If you’re already overweight, then you can improve your leptin sensitivity by restricting your calorie intake, eating mostly whole, minimally processed, nutrient dense foods, and exercising regularly.

If you’re lean and looking to get even leaner (less than 10% body fat for a man and 20% body fat for a woman), then you’re going to experience the negative effects of low leptin at one point or another no matter what you do.

One trick you can do to temporarily boost leptin levels, though, is to increase your calorie intake for two to three days periodically throughout your diet, mostly in the form of carbs.

Do that, and you’ll have a much easier time losing fat, maintaining muscle while cutting, and staying lean when your diet is over.

Oh, and if you liked this article, please share it on Facebook, Twitter, or wherever you like to hang out online! 🙂

What’s your take on leptin and weight loss? Have anything else to share? Let me know in the comments below!