Hunger: friend or foe for your body weight?
Hunger is one of our strongest instincts – and one of the sneakiest. It isn’t simply the feeling of an empty stomach, but a complex hormonal interplay that affects your mood, sleep, energy and how successful your weight loss will be. Understand hunger, and you understand your body.
Why do we get hungry?
The feeling of hunger is regulated by two opposing signals: a hunger signal and a satiety signal. Behind them are hormones produced mainly by the stomach and intestines, which are in constant communication with the brain. The stomach, blood vessels and gut talk to the hypothalamus, a small brain structure that acts as a kind of dictator of hunger and fullness. It is the hypothalamus that decides how much is enough and how appealing the food in front of us seems.
One important distinction: hunger is the physiological need to eat, whereas appetite is a psychological desire for a specific food. Both exist, but they are not one and the same thing.
Meal timing and satiety are also linked: the earlier in the morning you eat, the stronger the feeling of fullness. This explains the old advice to get most of your daily energy at breakfast and lunch – the body later learns to recognize satiety signals more easily.
Ghrelin – hunger that follows the clock
When a meal has been digested and blood sugar drops, the stomach releases ghrelin. The longer you go without eating, the more ghrelin is produced. As soon as your energy needs are met, ghrelin levels fall. Once the food has been digested, they rise again.
Ghrelin release follows the circadian rhythm: levels rise between midnight and morning, which is why hunger conveniently arrives in time for breakfast. This is no coincidence – it is a mechanism shaped by evolution. If you sleep poorly, this rhythm is disrupted and morning hunger is stronger than usual. It isn’t a question of willpower, it’s a question of hormones.
NPY and carbohydrate cravings
Alongside ghrelin, the stomach also produces neuropeptide Y (NPY). NPY is another hunger hormone, but its special role is to stimulate carbohydrate intake. Receptors in the central nervous system recognize NPY, and this directly influences our behavior.
High NPY levels suppress serotonin, the so-called feel-good hormone, in the brain. Serotonin affects mood, sleep quality and libido, and it also holds back the onset of hunger. Carbohydrates, in turn, raise serotonin levels. This makes it clearer why a low-carbohydrate diet brings on wild cravings for pasta or bread: the body is trying to raise serotonin and push NPY down. It’s chemistry, not weakness.
NPY also influences the sympathetic nervous system (SNS), which prepares the body for various activities – including the release of the stress hormones adrenaline and noradrenaline. An active SNS suppresses hunger: in the middle of training, hunger is very unlikely to catch us off guard. NPY, however, puts the brakes on the SNS. The result: fatigue and the urge to sit on the couch rather than walk the dog or go to the gym.
A typical breakfast is often rich in carbohydrates – and that is largely explained by NPY levels that have risen overnight. At the same time, it is also learned behavior, shaped by our culture. Both factors are at play.
Hunger on a diet: why does the body adapt?
You may have noticed that in the middle of a diet your metabolism seems to slow down. This happens for several reasons. First: a lower body mass simply burns fewer calories. Second: NPY plays a role – it suppresses insulin sensitivity and increases the activity of the enzymes responsible for storing fat. The body tries to conserve as much energy as it can, which is not great news for anyone who wants to get rid of body fat.
On top of that, with prolonged calorie restriction, production of thyroid hormone (T3/T4) and body temperature both drop. A normal body temperature signals a normal metabolism, but the body begins to give up this luxury by lowering its temperature. That slows the metabolism down even further. From an evolutionary standpoint, it’s a sensible protective mechanism – your body doesn’t know you’re dieting voluntarily; it thinks hunger is an emergency.
Frankly, the effect of quite a few popular weight-loss pills is based precisely on activating the SNS, which releases stress hormones and reduces hunger. But that doesn’t restore hormonal balance – it only temporarily silences one signal.
FAQ
Why do I feel strong hunger in the morning even when I ate well the night before?
Ghrelin levels rise through the night and peak by breakfast. This is a normal physiological process – your body is preparing for the day. Poor sleep amplifies this effect.
Why do I get wild cravings for carbohydrate-rich food on a diet?
Calorie restriction raises NPY levels, which stimulates carbohydrate intake and suppresses serotonin. Carbohydrates ease this cycle. It’s a hormonal reaction, not a personal weakness.
Can hunger be controlled?
Partly, yes. Regular sleep, consistent intervals between meals and a protein-rich breakfast help keep ghrelin and NPY levels more even. Sleep is the key factor here: when you sleep poorly, hunger hormones are significantly higher in the morning.
Translated from Body magazine; Author: Martin Berkhan
Author: Greta
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