Your Tummy is Ghrelin(Growling) For Food
By: Winnie Chang
When we eat food or even think about eating, our sugar levels rise. The pancreas is notified to pump out insulin and stimulate glucose uptake from blood. The liver stimulates glycogen formation which essentially lowers your blood sugar. In reverse, the pancreas will release glucagon when there is not enough blood sugar. The liver then stimulates glycogen breakdown which ultimately raises the blood sugar.
When you eat, there is an increase in glucose and fat. The more food you eat, the more fat there is present. The increase in fat cells means an increase in leptin as well. The body stores the fat and develops leptin resistance. As this occurs, the brain does not get the signal and thinks there is not enough energy. The brain cannot detect the leptin levels and starts producing food cravings. These food cravings lead to the issue of overeating.
Insulin, glucose, leptin, and ghrelin are all part of an extended familiy. Insulin is from the pancreas. Leptin is from the white adipose tissues. Ghrelin is from the stomach. Although from different body parts, they have a common goal of keeping the body in balance. They all help the brain control the energy balance between expenditure and food intake. They are also motivated by something similar: FOOD! Think of ghrelin as the hunger hormone. Before eating, ghrelin is produced by cells in the gastrointestinal tract. When you are hungry, there is low leptin and high ghrelin. Since there is low leptin, the brain tells you that you want food, hence the food cravings. After eating, the leptin hormone is made by adipose tissues. After you finish eating, there is high leptin and low ghrelin.
Time for Ghrelin 101. Ghrelin is the hunger hormone that acts on the vagus nerve and pancreatic beta cells to inhibit insulin release. It can pass through the blood brain barrier (BBB). It targets the hypothalamic system and the orexigenic ventral tegmental area (VTA). Instead of the nitty gritty stuff, lets talk about how it is important in the body. Ghrelin increase appetite which causes food intake and leads to the fluctuation of fat storage. It is implicated in food reward behavior, obesity, stress, addiction, and depression. Reward and motivation behavior are heavily influenced by external factors. There are two types of motivations: natural and synthetic. Food and sex are considered natural motivations whereas different types of drugs, alcohol, and addictive substances are considered synthetic motivation.
Notice how sometimes you eat food because you are hungry and sometimes you eat food just because you want to? Those are the two reasons we tend to eat food. The food reward is broken into two components. The first one is the motivational “wanting” beahvior. This is goal directed behavior where we forage for food and need it to survive. Our survival instincts kick in and tell us we need food. The second one is the hedonistic “liking” behavior. This is simply when we want food for food’s sake. That fancy slab of steak and lobster tail or gorgeous cookies and cream dessert just look so mouthwatering. You must have it to experience heaven in your mouth. You don’t actually need it, but you like it.
Sometimes eating food can have a rewarding feeling or value attached with it. This is because the rewarding value is dependent on hunger level and availability of food. When there is more food available, the motivation is low and the hedonistic behavior is high. Since there is enough food for survival, the food now is for pleasure. In contrast, when there is less food available, the motivation is high and the hedonistic behavior is low. There is a scarce amount of resources and therefore the behavior exhibited is more motivational as opposed to hedonistic. The food would be more for survival reasons as opposed to for pleasure. This motivational behavior can be traced back to the endocrine gut-brain system.
Remember how I said glucose, insulin, leptin, and ghrelin are all extended family members? Well ghrelin responds to glucose. In the normal glucose and insulin cycle, ghrelin release is stimulated and inhibited. When there is low blood glucose, ghrelin release from the stomach is release. On the other hand, when there is high blood glucose, ghrelin release is inhibited. As a part of the survival mechanism, norepinephrine increases ghrelin release as a part of the sympathetic nervous system. The sympathetic nervous system is the nervous system that reacts when you are stressed. Body temperature is elevated and there is increased arousal and locomotor activity. This reaction is a response to stressful environments and the possibility of starvation is considered stressful.
When you are hungry and your body notices a nutrient shortage, there is an anticipatory phases where it cues your vagus nerve. The superchiasmatic nucleus(SCN) stimulates ghrelin release. This is why there is a increase in ghrelin before meals. Decreased food anticipatory behavior means that ghrelin is suppresed. After meals, there is not a food anticipation and therefore a lowered level of ghrelin.
Eating at random times during the day can really throw off the balance of the different hormones and pathways in your body. Having a regular eating schedule lets the systems in your body know when to expect changes in glucose and fat levels and when to react. Think of it as having a regular work schedule. Knowing when to go in for work and when to get off work is better than being on call 24 hours a day. The sudden notice of needing to go to work can throw you off. Similarly, the sudden alert that certain hormone levels in your body have changed can throw your body off balance. This causes certain organs to overcompensate for other functions and your body will be extremely exhausted.
Lesson of the day: Eat regular meals so your adipose tissue, pancreas, and stomach can help your brain do its job easier to regulate the balance between energy expenditure and food intake.
Stay tuned for more about regular eating and how that affects your circadian rhythm.
