What causes us to be full?
Often we think that we are the ones to decide whether we are hungry or not, and therefore we determine when we eat and how much.
The hypothalamus in our brain is the structure that controls our hormones, while ghrelin is a hormone produced and released by our gastrointestinal system when we are hungry. Leptin is created by fat and travels through the bloodstream to the brain, which then stops the feeling of hunger.
We forget that we are driven by our own body, which is constantly making sure everything stays in balance including our blood pressure, heart rate, and weight.
Our body is a complex factory of nerves and hormones with a director who loves rest and balance. Our weight is not simply something we can decide for ourselves.
So read on to understand the science behind it.
Table of Contents
What causes us to be full? Introduction
The balance of our weight is determined primarily by the hypothalamus, an area in our brain that uses hormones to send signals and coordinate the body.
We cannot decide not to grow, nor can we choose to be hungry or not. We eat when we are hungry.
But where does this hunger come from? And what gives us a sense of satiety, and what causes us to be full?
Both are caused by chemicals that signal in our bodies.
Our hunger headquarters are in the hypothalamus
So the place in our head that What causes us to be full or hungry is the hypothalamus, hence the hypothalamus is in charge of our weight.
If it is damaged, then the adjustment point of our weight is broken.
Your ideal weight is the weight (often from the past) you felt good about for a very long time until something made you keep gaining weight.
Or it’s the weight you’re at now where you keep noticing that you always end up at.
The hypothalamus controls all the hunger and satiety hormones in our bodies to ensure that signals are sent out in the event of gaining or losing weight.
These signals then make us do more or less of something, whether eating, exercising, or just resting and digesting.
The hypothalamus makes the body always strive for that ideal weight again. So the hypothalamus is like a thermostat.
In most children, you can see this very clearly. There, the set point of the ideal weight has not yet been affected, so children:
- grow in height, which is also hormonally determined;
- in puberty eat more because they grow, and aren’t growing because they eat more; and
- maintain their weight because of this unaffected set point.
Ghrelin makes us hungry
Ghrelin is an example of a hunger hormone made by our gastrointestinal system when we are hungry.
We feel less hungry when we eat simple carbohydrates (ice cream, white bread sandwiches). Shortly after, the level of our hunger hormone ghrelin drops. But after two hours, ghrelin begins to rise again.
After three to four hours, ghrelin is higher than before eating, and you are hungrier than ever. This is also the time when your blood sugar is very low.
For example, fast carbs affect your hunger hormone so that you get a false hunger feeling.
Ghrelin reacts very differently to proteins and fats and does not dip and still provides a full feeling hours after the meal.
So you get hungry from eating the wrong things.
In overweight children, the hunger and satiety hormones appear to respond differently. However, ghrelin reacts very differently, and so does the gut hormone peptide tyrosine or PYY.
An experiment with children between the ages of 7 and 11 showed that overweight children were much less satiated after a meal with simple carbohydrates and became hungry again more quickly than children of average weight.
The hunger signaling function when eating protein and fat was not impaired in overweight children.
- Foster-Schubert, et al., Acyl and Total Ghrelin Are Suppressed Strongly by Ingested Proteins, Weakly by Lipids, and Biphasically by Carbohydrates, The Journal of Clinical Endocrinology & Metabolism, 2008
- Parvaresh, et al., A high carbohydrate, but not fat or protein meal attenuates postprandial ghrelin, PYY and GLP-1 responses in Chinese men, PLOS ONE, 2018
- Lomenick, et al., Effects of Meals High in Carbohydrate, Protein, and Fat on Ghrelin and Peptide YY Secretion in Prepubertal Children, The Journal of Clinical Endocrinology & Metabolism, 2009
Leptin tells us we’ve had enough
In his book Fat Chance, Dr. Robert Lustig (a pediatric endocrinologist) describes how he dealt with children who were being treated for a tumor or a lump in the head.
After they recovered well, however, the children developed a new problem. The children recovered after surgery, and the tumor was gone. However, the majority became too fat.
Not a little bit overweight but morbidly obese. All sorts of things were done to get the children to lose weight again.
It seemed that something from within was fueling the fatty tissue. He couldn’t solve it with character or willpower. Something made the children have to eat or move less.
Just as your hair grows and your nails grow, whether you want them to or not, fat tissue was increasing in these children.
The adipose tissue was like an alien taking over the body, an insatiable monster drawing all the calories to itself.
This was to the detriment of essential energy needed for the muscles and brain, which thus received too little. The children were found to be obese and malnourished at the same time!
How can this be? When we eat, we don’t eat indefinitely. At some point, we are full. After all, our adipose tissue is not just useless fat doing nothing.
Among other things, our fat makes a hormone called leptin. This is created at the time we are eating for about twenty minutes. As such, adipose tissue communicates with the brain.
The leptin travels through the bloodstream to the brain and arrives at the hypothalamus. The hypothalamus sees the leptin and translates this as a signal to stop eating.
In the children, this satiety center was damaged (by surgery or radiation). The hypothalamus was no longer able to read the message from the leptin.
The leptin was sent on its way by the adipose tissue, but the satiety center was damaged to such an extent in the children that the message could not be read.
If the message doesn’t get through, you’ll keep on eating. While the body is satisfied, you don’t experience it that way. To experience this, your satiety center must be working properly.
If the brain doesn’t pick up the signal, the adipose tissue figures the message mustn’t be strong enough since calories keep coming this way, so leptin production only increases.
This work has shown that our eating behavior is not purely a matter of our will, influenced by hormones.
When those hormones either don’t work correctly, or our brains don’t pick up the signal properly, we start eating differently as compensation.
Our eating behavior is thus a consequence of hormonal imbalance and not purely a problem of a greedy character.
- Lustig, et al., Risk Factors for the Development of Obesity in Children Surviving Brain Tumors, The Journal of Clinical Endocrinology & Metabolism, 2003
What causes us to be full? Conclusion
There is still a lot of work to be done on this front, because it is obviously not so simple that all overweight people have a damaged satiety center.
But it is also clear that not all overweight people are massively gluttonous. So that in itself is quite a liberation. We are finally beginning to see that cravings can be driven from within.
Research shows that in many overweight people, leptin is present but not working properly. So these people don’t get the same feeling of satiety.
This puts hunger and eating behavior in a whole new perspective, making us think twice before pointing fingers and blaming the individuals for lack of willpower or character.