Hunger Hormones – How Does the Brain Know When We’re Hungry or Full?

Hunger Hormones – How Does the Brain Know When We’re Hungry or Full?

By |2018-05-29T23:26:30-05:00April 4th, 2017|

Have you ever caught yourself mindlessly eating with little awareness of hunger, only to realize that “handful” of crackers turned into the entire box? Or, on the flip side, been so caught up in your busy day that you forgot to eat altogether, only to suddenly discover you are absolutely ravenous? If so, then you have experienced the sometimes puzzling effects of specialized signaling molecules in the body, formally referred to as “the hormones of appetite and satiety.”

There is a significant correlation between these recently identified hormones and how the gut communicates with the brain to regulate weight. This relationship is currently the subject of intensive research (mostly on mice) with researchers and field experts digging for clues that will help people quickly lose excessive weight, while keeping it off for good.

One great thing about these studies is that they are finally helping everyone involved recognize that weight loss is not simply a question of mind over matter!

Hunger Hormones – Signaling “I’m Hungry” — or “I’m Full”

This is a mixed cast of characters, some pressing the “Yes, I’m hungry” button while others pull the “No, I’m not” lever. Curiously enough, some do both. Several of these are well-known hormones while others are only newly discovered. Together they are carrying much of what manages our eating behaviors. Here is a quick overview of this complex and fascinating network.


The most predominant “hunger hormone” identified to date, ghrelin is a peptide released by endocrine cells mostly within the stomach’s lining. It counteracts leptin to increase metabolic efficiency and stimulate appetite. It normally indicates hunger: “If your stomach’s growlin’, you’re making ghrelin.” Though, it can also be released after a high-protein meal.

Neuropeptide Y (NPY)

This is an extremely potent stimulator of feeding behavior. It is also the most abundant neuropeptide in the brain. In addition to its function in feeding behavior, it also takes part in circadian rhythms, sexual functioning, and anxiety responses. Clearly, NPY is a key player! Much research is being done on this hormone as many are very invested in finding out what the magic answer is for obesity.


From leptos, the Greek word for “thin,” leptin is synthesized within fat cells, and works as a “satiety factor” on the hypothalamus to dampen eating behavior while increasing energy expenditure. Leptin appears to act, at least in part, by inhibiting NPY synthesis and release in the hypothalamus. New hopes of a magic weight-loss pill based on leptin have yet to reach fruition.


This is a mixture of anti-inflammatory peptides secreted by fat cells. It helps regulate energy balance and the metabolism of sugars and fats, as well as increasing insulin sensitivity. Paradoxically, overweight people often have less circulating adiponectin than slim individuals. What triggers its secretion from fat cells is still unclear. More than likely this is a very complex system that will take some time to understand.

Peptide YY (PYY)

PYY has been shown to slow digestion, suppress appetite, and significantly reduce food consumption.

Cholecystokinin (CCK)

CCK Is released in the duodenum in response to high-fat or high-protein meals. It signals the brain to produce a sense of fullness or satiety. Fatty meals are an especially effective trigger in the release of CCK.

Hunger’s Messages: What Our Other Hormones Have to Say

While it is tempting to think of the above hormones as “niche” players with somewhat specific effects on our desire to eat, the reality is that we don’t fully understand their effects. Many of our more well-known hormones still play into the equation. When it comes to natural weight loss, the hormones that regulate metabolism play an enormous role, with the three major hormones in the body: insulin, cortisol, and thyroid hormones, having the most to say.


Any discussion about hormones, metabolism, and healthy weight would be incomplete without including this major player in the hormone scenario. Insulin determines whether blood sugar gets used right away for immediate energy, or is alternatively stored as fat. Furthermore, because fat is not simply a passive energy-storage site (as previously thought), but functions as an endocrine organ that produces important hormones itself, what we eat really does matter when it comes to losing weight and keeping it off. Insulin levels are directly impacted by our diets, particularly the ratio of carbohydrates to fiber, fat, and protein. Any disruption in the insulin-regulating mechanism, such as insulin resistance, has an immediate influence on several of the lesser metabolic hormones. For more information, read our many articles about insulin resistance.

Thyroid Hormones

These may also play a lead role in everyone’s unique physiology. Women ask me daily whether a recent increase in weight could be due to a thyroid imbalance. While the thyroid does act very much like a gas pedal in regulating your metabolism, we most often find its relationship to weight gain is more indirect. Sluggish thyroid function is a consequence of an imbalance between other hormones.

Stress Hormones

Adrenal imbalance caused by excessive anxiety, stress, and cortisol production is typically at the top of the list when it comes to the correlation of unwanted weight and hormonal imbalance. Sustained high cortisol levels can lead to intense cravings and binge eating. High cortisol production can throw off any or all of the other hormones in the body, major or minor, setting off a chain reaction that leaves your body in chronic crisis mode. The simple significance of this is that no diet will succeed if you are under tremendous stress, no matter what you do. A simple saliva test can reveal whether your daily cortisol levels are in line with where they need to be. For more information, read our many articles about Adrenal Health.


The hormone that regulates the circadian rhythm also factors into your hunger time-clock. Research shows that sleep deprivation throws off melatonin production, which in turn influences leptin and ghrelin production. In one study, subjects who were chronically sleep deprived had 15% more ghrelin than those who were well-rested. There is also some evidence that lack of sleep affects your levels of human growth hormone (hGH), because “pulses” of hGH are released at night.

Sex Hormones

Let’s not forget estrogen, progesterone, and testosterone, also known as the minor hormones. Adequate levels of estrogen seem to help in hunger regulation, simulating the soothing “full” or satiety effect of serotonin. As anyone familiar with premenstrual binges can attest, an imbalance in the ratio between estrogen and progesterone can trigger intense food cravings. Add in the negative effects of stress hormones, and one begins to understand why women accumulate abdominal fat during perimenopause. For more information, see our extensive list of articles in our section about perimenopause and menopause. If a woman is testosterone-deficient, which can occur with poor nutrition or during perimenopause, she will have difficulty building muscle mass no matter how much she works out. Testosterone production relies on adequate levels of cholesterol, the building block of all sex hormones. This is why we so often will not suggest a low fat diet.

Hormonal Balance on Every Level

Modern research is showing that several varying hormones transmit or dampen hunger signals, which directly and indirectly influence our best efforts to lose weight. However, we still have a long way to go before we fully understand how the hormones of appetite and satiety actually work in the human body.

What we now know is there are very real hormonal factors involved. it’s not just your genetics, willpower, or eating habits. It takes a fine balancing act of each of these elements to even out the weight equation that leaves so many women struggling. As we uncover new pieces to the inner workings of our metabolism, we can see clearly how crucial hormonal balance can be to naturally shedding weight and keeping it off for good. Over the years, I have helped many women with the frustrating and complicated issue of successfully balancing their hormones, safely and naturally, to lose unwanted weight.

What About Willpower?

To a woman struggling to lose weight (and to keep it off) the notion that willpower alone should suffice is a lonely one. When it comes to keeping weight down, it is critical for an individual and her health care provider to keep in mind that relying on dietary discretion varies tremendously between individuals; depending on the variables at play it can even vary widely within one individual at different times.

What is important to understand is that our behavior around eating is not always something we can or do consciously regulate. Much of it is truly physiological, and physiology strongly impacts psychology.

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