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Weight loss & hunger hormones:
Why "willpower" may not be your problem.


Considering another strict diet? Short-term, very low-calorie intake disrupts powerful hunger hormones that control appetite and satiety. Crash diet now, feel hungrier later… even several months later.


What is the top New Year’s resolution? Lose weight.

Every year, people with good intentions set out to lose weight, only to have even more weight to lose the next year later. (Resolutions seem like such a good idea when you’ve got a party horn in your hand and a gold cardboard top hat on your head, swimming in a champagne-induced fog.)

One problem is that people try to lose weight quickly. Unfortunately, even if they manage to drop a few pounds fast, they bounce right back… and, often, keep on gaining.

By slowing down the weight loss process and teaching lifelong healthy habits, PN Coaching is designed to avoid the cycle of perpetual weight loss.

Now, research confirms our methods. (But we knew that already.)

Only slow and steady progress leads to lasting change. Why?

Appetite hormones: Why self-control is not the problem

Myth: Weight loss is all about self-control.

People berate themselves or are judged by others for carrying a few extra pounds. To be fat means you’re weak-willed, spineless, and/or impulsive.

Fact: Powerful hormones control our perception of appetite and hunger, as well as our eating behavior.

While you still have the option of self-control, your body definitely has a strong voice in the matter. And willpower breaks down easily under stress; when blood sugar is low; and/or in environments that don’t support weight loss (like an office where everyone has a candy dish and it seems like someone has a birthday cake every day).

Here are some of the more well-known hormones that influence appetite, hunger, and satiety.

Hormone Effects
Cholecystokinin (CCK) Released in the small intestine when fats and proteins are eaten. Receptors that respond to CCK are not only found in the gut but also in the brain. In the brain CCK depresses hunger, meaning the more CCK you have floating around the less hungry you are, and the less you’re likely to eat. This is why a lower-carb, higher-protein, higher-fat diet tends to make people feel fuller longer.
Glucagon-like peptide-1
Delays stomach emptying time that may make you feel more full.
Gastric inhibitory polypeptide YY
Secreted by small bowel and colon in response to food. Inhibits hunger.
Leptin  Mostly released by fat; decreases hunger. If you want to lose weight you’d want to have more leptin.
Ghrelin  Made mostly in the stomach; acts on the brain (hypothalamus) to stimulate hunger. If you want to lose weight, you want less ghrelin.

For more about leptin and ghrelin take a look at another research review of mine.

The ideal hormone combo to suppress appetite and help you lose weight would be:

  • more CCK, GLP-1, PYY, and leptin
  • less ghrelin

What happens to hormones over the long haul?

The study I’m reviewing looks at what happens to appetite hormones after 10 weeks of dieting up to a year later. Yup, your lemon-cayenne diet from last year may be making you feel more hungry this year.

Sumithran P, Prendergast LA, Delbridge E, Purcell K, Shulkes A, Kriketos A, Proietto J. Long-term persistence of hormonal adaptations to weight loss. N Engl J Med. 2011 Oct 27;365(17):1597-604.


This year-long study involved 50 people with BMI between 27 and 40 (classified as overweight and obese), who went on a crazy low-calorie diet for 10 weeks (though the researchers called it a very-low energy diet).

What’s a crazy low-calorie diet? Oh, say 500-550 kcal for people that had an average weight of 95 kg (209 lb), which is one-third of their basal metabolic rate.

To live without moving at all, these volunteers would need about 1700 kcal on average. No question they were really hungry and needed a hell of a lot of willpower to stay on this diet.

Basal metabolic rate.

BMR is the amount of energy you need to live when at rest. The most common equation to calculate BMR is the Harris-Benedict equation.

BMR calculation for men

BMR = 66.5 + (13.75 x weight in kg) + (5.003 x height in cm) – (6.755 x age in years)

BMR calculation for women

BMR = 655.1 + (9.563 x weight in kg) + (1.850 x height in cm) – (4.676 x age in years)

Here’s an online BMR calculator.

Here’s our Calorie Calculator.

The problem with calorie math

This intake of 500-550 kcal means that each day these volunteers are eating at least 1200 kcal less than they need.

Since fat has 3600 kcal/pound, you could use basic (and flawed) calorie counting to figure they should lose a pound (0.45 kg) of fat every three days. At the end of 10 weeks (70 days) they should lose just over 23 pounds (10.6 kg), or 11% body weight in fat.

The problem with thinking of yourself as just fat that’s burned like a candle is that you overlook things like hormones that through evolution respond to starvation by storing calories more efficiently.

A few hundred years ago, it was a good thing that your body responded to starvation by storing as much fat as possible. Thrifty hormones saved lives. Now when starvation is self-induced in a sea of food it causes problems.


During the first 10 weeks of the study, when the volunteers were eating a very low calorie diet, they lost 9.4 kg (20.7 lb) of fat and 4.1 kg (9 lb) of lean body mass, but that didn’t last over the next year.

As the year went on after the diet, they slowly gained half the weight they lost. At first glance, that doesn’t sound too bad. They lost a fair bit of weight in a short period, and then a year later, they were still ahead of the game.

Hormonal effects: short term

The problem is what happens to these volunteers’ hormones — the hormones like leptin, ghrelin, peptide YY, etc. — that regulate appetite, hunger, and satiety.

After 10 weeks of starvation the volunteers had less leptin, peptide YY, and cholecystrokinin, as well as more ghrelin and gastric inhibitory polypeptide. The result: The volunteers felt more hungry. Cue the need for even more willpower to keep the weight off. Sound familiar?

Hormonal effects: long term

We knew that crash dieting messes up appetite regulatory hormones for a short period, but until now, nobody had looked at the long-term effects of very low calories on these hormones.

Why didn’t anyone look at what happened a year or more later?

Well, it’s hard to get people signed up for a year-long anything, let alone having them go on a starvation diet for over two months first. Plus, it’s a bit of a surprise that a short-term diet would do much a year later. These scientists must have had to convince a lot of people that this study was worth doing.

One year after dieting the volunteers still had less leptin, peptide YY, and cholecystokinin; and more ghrelin, gastric inhibitory polypeptide and pancreatic polypeptide.

What happened to hunger? Still higher after a year. Think about that. A full year after dieting, the volunteers still felt more hungry. No surprise that most dieters regain weight lost and more… eventually.


If you try to lose weight quickly, you’ll end up trying to lose it every year instead of taking a year to lose the weight once.

It’s clear that very low calorie dieting has long term impact on hunger and appetite hormones lasting at least a year. Now imagine what multiple crash diets might do.

By the way, stringent and chronic restriction also affects hormones that control gastric motility (the speed at which food is processed) and neurotransmitters (brain chemicals).

Thus, if you regularly “diet”, not only do you end up always hungry, you have indigestion and “brain hamsters” like anxiety or depression, and you rarely feel psychologically satisfied by eating — you always want more, or have strong cravings. Show me a “professional dieter” and I’ll show you someone who feels generally lousy physically, mentally, and emotionally. Hormonal disruption is strong stuff.

Could yo-yo dieting lead to cumulative changes in appetite regulation hormones? Very likely. Several years of yo-yo dieting later, you may feel much more hungry than when you started. Good luck with willpower then.

Bottom line

Lose weight quickly while nearly starving, only to gain most of it back (or more) and feel hungrier than when you started. Or lose weight slowly, for good, and feel better than ever… eventually.

What would you choose? If you want door #2… well… have we got a program for you.

Want help becoming the healthiest, fittest, strongest version of you?

Most people know that regular movement, eating well, sleep, and stress management are important for looking and feeling better. Yet they need help applying that knowledge in the context of their busy, sometimes stressful lives.

Over the past 18 years, we’ve used the Precision Nutrition Coaching method to help over 100,000 clients lose fat, get stronger, and improve their physical and mental health… for the long-term… no matter what challenges they’re dealing with.

It’s also why we work with health, fitness, and wellness professionals (through our Level 1 and Level 2 Certification programs) to teach them how to coach their own clients through the same challenges.

Interested in Precision Nutrition Coaching? Join the presale list now. You'll get a free gift today, save up to 54%, and have the chance to secure a spot 24 hours early.

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If you’re ready to change your body, and your life, with help from the world’s best coaches, this is your chance.

[Note: If your health and fitness are already sorted out, but you’re interested in helping others, check out our Precision Nutrition Level 1 Certification program].


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