Back To CourseNutrition 101: Science of Nutrition
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Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.
Appetite, or your desire for food, is a constant in life. This is a good thing because food provides the body with nutrients needed to keep you going throughout your day. You literally eat to live, yet having too much desire to eat can make you feel as if you are living to eat and lead to unwanted pounds and health problems. All of us have been drawn in by the tempting smell of fresh baked cookies straight out of the oven, yet the true driving force behind what makes you want to eat is a fairly complex interaction between your body and your brain.
You take notice to your appetite when you experience hunger, which is the uncomfortable feeling caused by a need for food. We have all experienced hunger; it only takes a few hours of not eating to trigger the sensation. This sensation is called hunger pangs, which is the discomfort felt in the abdominal region associated with contractions of the empty stomach.
Appetite and hunger are sometimes used interchangeably, yet they are not the same thing. You can have an appetite without being hungry. If you ever wanted to eat a piece of chocolate cake after a big meal, even though your body didn't need the calories, then you know what I am talking about.
To best understand what stimulates appetite and hunger, it is good to build our basic understanding of how the body handles and stores nutrients. The body's main source of fuel is glucose, followed by fatty acids or lipids. When you eat carbohydrates and fats, these fuels are absorbed into your bloodstream to be used immediately for energy or to be stored in body cells for later use. When your body's storehouse of nutrients is depleted, appetite and hunger are initiated.
Knowing this gives us the big picture, yet at the same time oversimplifies matters. After all, regulating appetite is not as simple as filling your car's gas tank and driving for 200 miles before needing the next fill-up. Instead, appetite and hunger are complex processes that involve the interaction of your brain and hormones, and they are further influenced by your habits, external cues and your emotions.
Let's start with a look at how hormones influence your desire to eat. Hormones are the emergency responders of the body and are constantly on alert ready to be released or suppressed in order to maintain homeostasis. The digestion and storage of nutrients involves the interplay of many hormones, but when looking at the hunger hormones, we can put most of our focus on just two.
The first is leptin, which is a hormone secreted by your fat cells that acts as an appetite suppressant. Leptin levels peak when you fill up on food. So, when you eat a lot, your appetite goes away. If you ever said, 'I am so full I couldn't eat another bite,' then in that moment, your body was flooded with leptin. It might help you to recall the action of this hormone by remembering that leptin lowers hunger.
Now that you are full, you will probably wait a few hours before eating again, and this brings the second hunger hormone into the game called ghrelin. Ghrelin is a hormone secreted by the stomach that acts as an appetite stimulator. If you ever said, 'I am so hungry that my stomach is growling,' then your body was flooded with ghrelin. So if your stomach is growling, then it is producing ghrelin.
Ghrelin communicates with your brain and triggers the release of an additional hormone called neuropeptide Y, which is a hormone secreted by the hypothalamus that stimulates hunger.
Your hypothalamus is the part of your brain that regulates appetite and hunger. In fact, your hypothalamus stays pretty busy with this function, taking in data from different sources. Tucked up inside your brain, this collection of nervous tissue receives inputs from the vagus nerve, which is actually a cranial nerve that sends signals from the gastrointestinal tract to the brain. The signals are reports on how distended your stomach is - in other words, how full you are. If you stomach is filled up with food, then hunger is suppressed.
The hypothalamus also receives input about the levels of hunger hormones that we discussed earlier and adjusts your appetite accordingly. In addition, the hypothalamus monitors the amount of lipids and sugars in your blood. If you haven't eaten in awhile, these levels begin to drop, and it's time for more fuel, so your hypothalamus releases the hormone neuropeptide Y to drive you to eat.
So far, we have taken a look at how your body regulates your appetite from a neurological and hormonal standpoint, but you may have noticed that there are other triggers that drive you to eat. There is some evidence that the sight of a delicious dessert, the smell of tempting fried foods and even the physiological effects of stress can increase production of ghrelin, which enhances your appetite. And, just like Pavlov's dogs were conditioned to salivate at the sound of the dinner bell being rung, humans have conditioned their bodies to expect food in response to external cues, such as the realization that the noon hour has arrived, signaling your lunch break.
Appetite is the desire for food that you experience as hunger, which is the uncomfortable feeling caused by a need for food. They are complex processes that involve the interaction of your brain and hormones as well as your habits, external cues and emotions.
The hunger hormones are leptin, which is a hormone secreted by your fat cells that acts as an appetite suppressant (leptin lowers hunger after a meal), and ghrelin, which is a hormone secreted by the stomach that acts as an appetite stimulator. If your stomach is growling, then it is producing ghrelin. Ghrelin communicates with your brain and triggers the release of an additional hormone called neuropeptide Y, which is a hormone secreted by the hypothalamus to stimulate hunger.
Your hypothalamus is the part of your brain that regulates appetite and hunger. It receives input from the vagus nerve, which is a cranial nerve that sends signals from the gastrointestinal tract to the brain and reports on how distended your stomach is. The hypothalamus also receives input about the levels of hunger hormones, lipids and sugars in your blood and adjusts your appetite accordingly.
There are other triggers that drive you to eat. The sight and smell of tempting foods and even stress can increase production of ghrelin, which enhances your appetite. You can be conditioned to expect food in response to external cues, such the clock telling you it is lunchtime.
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Back To CourseNutrition 101: Science of Nutrition
17 chapters | 155 lessons