Hunger and Appetite
The complex systems that encourage us to eat
Every action in the body – whether it is the heart beating, leg muscles contracting when a person walks, the brain processing the contents of a conversation, or an arm moving to scratch a nose – requires energy. We get this energy from the calories in food, either directly after we eat or from the calories we store in our bodies as glycogen (in the liver and muscles) or as fat. Since getting enough energy, along with other nutrients, is incredibly important for our survival, our bodies send hunger messages that encourage us to eat.
Defining Hunger
There are many ways to define hunger. When policymakers or international aid groups speak of hunger, they are usually referring to the inability to eat enough food for a sustained period, typically through poor accessibility, scarcity, and/or poverty. While less common in Canada than in developing nations, there are still individuals in Canada who struggle with this type of hunger, such as those living under the poverty line and those located in remote regions with inadequate access to food.
Generally, the type of hunger we think of most often is the one that everyone is familiar with: the temporary discomfort of needing to eat, including symptoms such as a rumbling stomach, mild light-headedness, and sometimes moodiness, dizziness, and nausea, coupled with a desire to consume food. We will be focusing on this kind of hunger.
What is Hunger?
A complex system of physical and hormonal signals cause what we know as hunger. It involves many parts of the body, including the brain, nervous system, pancreas, stomach, and the rest of the intestinal tract.1 There are two primary hormones involved in hunger signals: ghrelin and leptin.2 When you haven’t eaten for some time, the stomach (and other parts of the digestive tract, to a lesser degree) produces ghrelin, which increases appetite, gastric motility, and gastric acid secretion. Ghrelin levels are highest right before meals, when your blood sugar is low and your stomach is empty. On the other hand, when you’ve eaten enough, fat cells secrete leptin, which interacts with the brain to say that you have enough calories in storage, and it is therefore time to inhibit hunger signals. A wide variety of other hormones are involved in hunger and appetite signals, including insulin and cortisol.3
Hunger vs Appetite vs Cravings
It’s a common occurrence, especially around the holidays: you feel stuffed after finishing dinner, then someone brings out the dessert and you seem to grow a second stomach. This isn’t true hunger, which occurs when the body demands nutrients to function, but rather appetite.
Hunger is physiological. It occurs because of biological changes throughout the body, which signal that you need to eat to maintain energy levels. Appetite is simply the desire to eat. It can be a result of hunger, but often has other causes, such as emotional or environmental conditions. For example, feeling very stressed, upset, or bored, or being exposed to food that looks or smells delicious, can increase appetite even when you aren’t really hungry. Being stressed, depressed, or distracted can also make you lose your appetite even when your body is hungry. Appetite can also be a learned behaviour. For instance, the desire to always eat at exactly the same time each day is often more from appetite than from hunger, or simply yielding to routine.
One test to tell if you are experiencing hunger or appetite is to consider eating a healthy food you don’t hate but don’t particularly enjoy. If you would eat this food, you are probably hungry, if you don’t want to eat that food, but you really want that cinnamon bun from the bakery you just walked past, it’s probably appetite.
A craving is the desire to eat a specific food. Cravings increase your appetite and can occur regardless of whether or not you are hungry. While some people believe that cravings are a sign your body needs certain nutrients from the food, there isn’t much research to support this belief. The type of foods individuals most often crave are rarely rich in nutrients that they might be deficient in but are often high in sugar and salt.4 However, nutritional deficiencies might play a role in pica, a condition that causes cravings for non-nutritive foods, such as ice and dirt. While it isn’t the case for everyone, many individuals with pica are deficient in minerals such as iron or zinc.5
Hunger vs Appetite
| Hunger | Appetite |
|---|---|
| in the body | in the brain |
| fuel | fun |
| need | craving |
| will eat most things | want specific foods |
| gradual | sudden |
| no trigger | often caused by a trigger |
How GI Diseases and Disorders Affect Hunger and Appetite
Some digestive conditions can cause a loss of appetite. You still need to eat so that your body gets enough nutrients, but these conditions can cause a reduction in the desire to do so for a variety of reasons. Individuals who experience frequent nausea often don’t have much of an appetite. It’s difficult to think about eating anything when your stomach is upset. People who regularly experience severe abdominal pain, diarrhea, and/or constipation might associate the consumption of food with these symptoms and therefore want to avoid eating. One condition, gastroparesis, causes food to stay in the stomach for too long, which can affect normal hunger signals and make it difficult to eat enough.
Factors That Influence Hunger
What you eat can have a large effect on your hunger and appetite levels. Foods that contain plenty of protein, fat, fibre, and complex carbohydrates tend to be more filling. This is because they take longer to digest, keeping contents in your stomach for longer and leading to a slower release of nutrients into the blood stream. Highly processed foods, particularly those that contain lots of simple sugars, can make you feel very hungry because they lead to rapid swings in blood sugar levels. Typically, blood sugar rises quickly after eating processed foods, then drops quickly shortly after, unlike the slow sustained release of glucose from complex carbohydrates.
In addition, lifestyle factors such as exercise and stress can affect hunger and appetite. If you exercise frequently, you will likely become hungrier, as your body needs more calories and nutrients to function. However, occasional exercise might suppress appetite in some individuals.6 Mood can have a huge influence on appetite. For example, being stressed, bored, depressed, or experiencing various strong emotions can change your appetite level. In some people, heightened emotional states can lead to an increased appetite, whereas others might find it very difficult to eat anything when they are experiencing strong emotions.
Medications can also affect appetite levels. In some cases, this occurs as a side effect, other times, your physician might prescribe a medication specifically to reduce or increase your appetite.
When Hunger Signals Go Wrong
Hunger and appetite are complex systems. While they generally work well, there is sometimes a problem with the signals. Genetic conditions, environmental influences, hormones, mental health conditions, and many other aspects can wreak havoc on normal hunger cues. The most common problem with hunger and appetite regulation in Canada is overweight and obesity, a chronic disease. There are many different causes of this disease, but obesity often involves problems with hormonal regulation of hunger and appetite.7
Conversely, there are people who experience a strongly reduced appetite. Individuals affected by certain diseases and disorders, such as infections, hormonal conditions, cancer, diabetes, and HIV/AIDS, can experience a reduced appetite, which can be a particularly dangerous symptom. Individuals who do not eat enough are at risk of symptoms such as fatigue, irritability, nutritional deficiencies, electrolyte imbalances, weight loss and, in prolonged cases of starvation, loss of vital tissues, refeeding syndrome, and death.