Ghrelin and the Pleasure of Eating.
Ever wonder why food seems to taste so much better after not eating for a long period of time? Well in reality the taste itself is still technically the same but how your body reacts to the eating of food while hungry, opposed to satisfied, is different. Eating food in general, tends to be very pleasurable but, let’s take a closer look into what is actually going on inside your body on a biological level when you eat food.
Though not much have been actually proven behind the mysteries of why eating is so pleasurable, one major player that has been observed is the hormone known as ghrelin. Our bodies are constantly in communication with its various parts, always communicating with itself. The brain is constantly speaking through nerves that run to every part of your body; giving out commands to your muscles to move, warning your stomach that it will soon be put to work, or telling the pancreas to release the right hormones at the right time. Of course this communication system is not one-sided. Certain organs of the body release hormones to signal the brain. Ghrelin is secreted by cells found in the stomach and produced when the stomach is empty. It then circulates through the blood until it reaches the brain, telling the brain that it’s time to eat again making us feel hungry. However, ghrelin release can also be initiated by the brain. When anticipating food or when feeling that the body may be in desperate need of sustenance, the brain will signal the gut through a vagus nerve for a ghrelin release. The ghrelin receptor, GHSR-1A, is found in many different brain areas that contributes to the control of food intake, especially the hypothalamic area, brainstem, and mesolimbic pathways. The hypothalamus and brainstem play major roles in maintaining the homeostasis of the body, in which food has a major impact on, and the mesolimbic system, also known as the reward pathway, plays a part in the pleasurable aspect of eating.
Ghrelin levels in the blood have been discovered to increase in the moments right before a meal and decrease after meals, once the body starts to ingest nutrients. Of course there are other factors that could be responsible for an increase in ghrelin other than an empty stomach. Glucose, which is a simple sugar that also circulates through the blood, can be absorbed by your cells and can be used later for energy. Low levels of glucose signal a possible shortage of energy and so stimulates an increase in ghrelin while high levels of glucose block it. Release can also be caused by a low calorie count, a negative energy balance, in which you are exerting more energy then you are taking it, or even psychological stress. When the body is under certain conditions, such as when experiencing stress due to school, your job, etc, ghrelin will be released. Yup, this results in stress eating! Due to the increase of ghrelin you will naturally want to consume more.
But what does this have to do with eating and pleasure? Well that pleasurable feeling you get when you eat is caused by the hormone dopamine. Dopamine mediates pleasure in the brain and is also released during sex or when taking certain drugs. Eating food has the same effect and triggers the release of dopamine. In the brain there are ghrelin receptors found on these dopaminergic neurons that release dopamine when ghrelin comes in contact with its receptors. During times of fasting, the amount of ghrelin in you blood is increased, resulting in a bigger dopamine release when you finally eat food. So though the food may taste the same, you brain finds more pleasure when eating after fasting. Even when not fasting we can observe the effects of ghrelin by blocking ghrelin signalling in the body. Without ghrelin signaling in mice, it was observed that there was a decrease in spontaneous food intake along with a decrease in body weight. Without ghrelin, we would be less inclined to overeating, however, we would also be giving up on enhancing the pleasure of any given meal.
If we look at this from an evolutionary point of view, since the body tries to keep its energy storage levels, having the reward pathways assist in regulating food intake gives organisms a higher incentive to seek and consume the nutrients that it needs. It encourages seeking out food during times of scarcity, but also encourages overeating during times of plenty so that the body may have sufficient stores of energy when food is once again scarce. Since food activates the reward systems in the brain it motivates organisms to go out and seek that which will provide it with energy and nutrients. Though this may be advantageous to wild animals, this trait in many of the human beings today may not exactly be beneficial. We have a natural desire to overeat in times of plenty, however, we are more likely not to experience a time of scarcity afterwards. Dopamine is released more when eating sweet and high-fatty foods, which usually means more energy, motivating humans today to eat high calorie foods at levels that go far beyond what the body actually needs. This may give a little bit of insight on the common question of ‘Why does everything that taste good bad for you?’ Calorie-dense foods aren’t technically bad for you, it is just the moderation in which we choose to consume it that could lead to unhealthy consequences.
Overall eating food can cause much pleasure, but when under certain conditions, your body can increase that pleasurable feeling with the help of ghrelin.