Being hungry can make you happy? Really?
Your body has a mission. It tried to keep you in a state of energy balance, and it needs you to cooperate in that. It needs you to put in and take out the right amount of calories, or energy in order to help it to maintain this energy balance. Ghrelin and Leptin are two hormones that help it in this mission by sending clear signals to your brain. In essence, ghrelin says, "I'm hungry", and leptin says, "I've had enough". Both hormones are relatively new discoveries and researchers are busy finding ways to influence ghrelin and leptin to help to reduce increasing obesity levels.
Leptin is a hormone secreted by your fat cells. When working properly, your body responds to leptin by decreasing your appetite after you've eaten. Leptin also promotes calorie burning. Though first discovered in experiments with mice, it seems to work in the same way in people, with a twist: Obese people have high levels of leptin, but researchers think their bodies are less sensitive to its effects. Leptin resistance, as it's known, results in "unnecessarily high food intake," and low leptin levels are a precursor to obesity.
Ghrelin regulated the opposite side of the equation as the hunger hormone - its job is to send a message that you need to eat. Like leptin, it works in the region of the brain in charge of pleasure-seeking, and researchers believe ghrelin also controls "stress eating," makes you crave high-calorie foods and seems to promotes abdominal fat. When you go on an extreme diet, even more ghrelin gets secreted, and your ability to burn calories starts to diminish. The stomach shoots a dose of ghrelin every 30 minutes, but it can speed up to about every 20 minutes if your tummy's empty and you're really hungry.
Here's the interesting part. Researchers manipulating levels of ghrelin in mice - including prolonged calorie restriction - came across some curious findings. Those mice that had low levels of ghrelin activity seemed to show depressed type behaviour (if you accept the premise that it is possible to ascribe such attributes to a mouse). In any case, when in deep water they appeared to make no effort to swim. When introduced to a maze, they clung to the entryway. When placed with other mice, they tended to keep to themselves. When they were given an antidepressant that is given to humans, these behaviours appeared to be reversed.
Is it possible that ghrelin haleps to regulate mood symptoms in humans too? The data presented in this study is suggested to offer support to the idea that chronic stress can elevate ghrelin levels, and this increased level of ghrelin circulating in the bloodstream can help to generate behaviour to counter the effects of the stressor. When these mice were placed in deep water, they swam energetically. When these mice were put in a maze, they eagerly looked for an escape route. When these mice were placed with others, they were much more social.
The same hormone that is responsible for telling you that you need to eat also seems to be responsible for all sorts of positive adaptive behaviours - at least in mice. In the wild, researchers think that hunger-induced positive behavior (could we call it happiness?) is adaptive. Trying to find food requires concentration, clear-headed perception and often, cooperative behaviour. If hunger made us walk around in a daze, instead of finding our dinner, we would increase the risk of ending up as someone else's dinner. Instead, the increased production of ghrelin and its psychological effects could motivate us to find food. But, another interesting twist is the fact that hunger isn't the only stimulus, or stressor, that can boost ghrelin levels. Social anxiety can stimulate it as well. When mice were exposed to an older, dominant, "bully" mouse, ghrelin levels rose and stayed high for weeks. Substitute "bully" mouse for overbearing boss or toxic work environment, and you can start to see some interesting parallels. Raised ghrelin could be why some people tend to overeat when feeling under pressure or stress. However, if can resist the urge to eat, then ghrelin can also help us to approach the situation in a calm, clear-headed manner and help us to change the situation in our favour.
The little 'happy' boosts of ghrelin when our bodies signal that we should eat could be reward mechanisms also underlie other complex behaviours, such as eating disorders such as anorexia nervosa, and why people with this disorder have such a difficult time recovering. It might also explain why practices such as intermittent fasting are so popular too.
We are complex little beings, and our perception and understanding of the external world with the sensations and feelings in our internal worlds can produce a dizzying array of different outcomes. Given that the existence of ghrelin and leptin are relatively recent discoveries, many more complexities may yet be still unknown to us, but we can take advantage of the knowledge as it is revealed.