Hunger is a feeling we all know very well, whether we are considered under, normal, or overweight. In many ways it is our pestering companion, reminding us, often too frequently, to fill ourselves up.
But how exactly does our brain control our feelings of hunger? In an orchestrated dance, your nerve cells within your hippocampus (area of the brain behind your eyes) interact with your hormones to send signals of hunger.
When you have finished eating and digesting your latest meal, and have used up that energy, your blood glucose and insulin levels will drop. When this happens, a hormone called ghrelin will be manufactured in the gut and then move up to the brain, where it will activate hunger-producing nerve cells and deactivates hunger-inhibiting nerve cells.
However, some people may be wondering why they experience feelings of hunger so often; and, for many, this has to do with hormone dysregulation. For example, another important hormone for hunger regulation is leptin, a hormone that suppresses the appetite. Unfortunately, some studies have shown that animals who lack certain levels of leptin will overeat and become obese.
Other studies have shown that humans are also susceptible to hormone dysregulation and overeating. In a study done with humans, those who were given injections of ghrelin responded much as the animals who had low levels of leptin; they showed enhanced responses in brain areas associated with rewards when shown pictures of food. Thus, when leptin levels are low and ghrelin levels are high, humans often experience more frequent and intense hunger.
Your brain is also responsible for those less-than-healthy choices we all are tempted to make. There’s a reason walking by that sugary treat activates feelings of hunger, and that is because you have had it before where it had given you a pleasurable experience, triggering dopamine. Thus, that feel-good hormone activated your reward system, signaling to you that the sugary treat will make you not only full but happy.
As for why some people eat more of these treats than others, researchers have various theories. One theory is that individuals who over-consume sugary and unhealthy foods have lower availability to dopamine, meaning they consume more than the typical eater to get that feel-good response. In fact, a study involving rats showed that the rats with lower dopamine receptors did gain weight and overeat.
Another theory postulates that over-exposure to such foods creates a hyper-dopamine-response to the foods, leading those people to seek out such foods in much greater quantity. Brain scans have shown increased functioning in relevant brain regions to both visual food cues and food anticipation, supporting this claim.
With these experiences with dopamine, eaters become programmed to eat in certain ways. These learned associations can trigger intense cravings for certain foods. Studies have shown that rats as well are highly susceptible to learned associations with food. In fact, both humans and rats will, when cues and context are right, override their feelings of fullness to eat, especially if the food is particularly tasty.
But with these cues around almost everyone, from typical eating times to effective food advertisements, how come some brains seem better able to resist the temptation to eat when not hungry? Unfortunately, this is just another way that your brain’s function regulates eating behaviors. Some studies have shown that those who are obese also tend to have impaired control, meaning they have a hard time inhibiting impulses and resisting temptation.
While some people may be more susceptible to frequent feelings of hunger due to cues and/or poor inhibitory control, others have emotions which cause them to experience hunger more frequently. For example, those who are depressed, anxious, and/or stressed will find their appetites greatly stimulated, much like those who are experiencing bursts of joy or anger. To the contrary, emotions of fear and sadness do not overstimulate the appetite like those other emotions.
The amygdala is the area of the brain responsible for allowing emotions to regulate feelings of hunger, and activation of the amygdala often predicts future consumption of unhealthy foods and future weight gain.
Of course, emotions aren’t just reasons you might be feeling hungry. You may also experience strong emotions in response to having hunger unsatiated. Neuropeptide Y, a chemical released during hunger, in high levels also leads to feelings of anger. Thus, while some people may make excuses for being angry when hungry, there might be some science behind their phrase “hangry”.