The Science of Hunger

Hunger is a daily part of all of our lives, and it seems to have a frustratingly high amount of control over our eating habits. In fact, curiously enough, according to livestrong.com, "Americans spend more money in dieting, dieting products and weight loss surgery than any other people in the world." Yet, according to the CDC, 62% of American adults are overweight or obese.

There are many perspectives as to why we feel hungry and how hunger impacts what we eat and how much of it. It is critical to know where our drive to eat comes from and how it functions, as this is the first step in understanding how to lead healthy lives. Below are three of the most widely accepted theories that explain where hunger comes from and what impacts someone's level of hunger.
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Why we feel hungry--3 theories

1. Drive-reduction theory
This theory states that our biological need for food leads to a psychological drive (hunger), which leads to a drive-reducing behavior (eating). Basically, we are hungry because our body needs food, and we eat to satisfy that discomfort and maintain homeostasis.

Homeostasis describes how our bodies are constantly trying to remain internally stable. When it comes to hunger, this comes in the form of set points. For instance, less food intake leads to less glucose in the body, and in an attempt to compensate, drive-reduction theory states that we feel hungry so that our body eats and our glucose level increases. This glucose level that our body is naturally pushing us to return to is called our glucose set point, and it differs for everyone. We also have a body fat set point, and if our fat stores drop too low, in order to decrease our energy output our metabolism slows and we feel more driven to consume food, which increases our body fat. This explains why it can be really hard to lose weight and maintain the results over a long period of time! More on hunger and weight later. : )

So what does this theory say about how our body creates our hunger drive? Well, our glucose level is monitored by receptors in our digestive system, and these receptors send chemical messages to the hypothalamus, a region of the brain responsible for appetite regulation, releasing hormones, and much more. When our glucose level is lower than normal, the hypothalamus is signaled to release hormones that stimulate appetite, such as the hormone orexin. When we eat a large meal and our glucose level rises to above normal, the hypothalamus is signaled to release hormones that curb our appetite so that we stop eating. Other hormones that are involved in appetite regulation include leptin, PYY, insulin, and ghrelin.

2. Instinct theory
This theory describes how our interactions with food are the result of genetics and human evolution. It claims that genetics dictate weight change patterns and appetite size.

Instinct theory also explains how humans' taste preferences are comparable based on genetics. Basically, across the globe, all humans are hard-wired to prefer foods that are sweet and salty. Everyone also may be genetically predisposed to dislike food that is new and unfamiliar, and develop revulsion to food that has made them sick in the past.

Although all people have 99.9% shared DNA, there are some genetic differences that affect how we perceive food. Not everyone has them, but some people have inherited special supertaster or nontaster genes that developed throughout human evolution because they increased survival in unsafe and safe environments, respectively. Supertasters perceive certain flavors as stronger than normal people do, while nontasters cannot taste the chemical phenylthiocarbamide, which tastes bitter to people without the nontaster gene. (To find out if you're a supertaster, nontaster, or medium-taster, visit this link!)

3. Incentive theory
The incentive theory claims that hunger is a learned response. According to this theory, if we follow an eating schedule we feel hungry accordingly. For example, if we normally eat breakfast at 9am, we get hungry if we don't eat at 9am because our body has been conditioned to expect the food at that time.

Additionally, the incentive theory claims that some people are motivated to eat when there is more food out in front of them. Just the sight of the food and the knowledge that it is available can cause people to eat more than they otherwise would. This is why people eat so much more at all-you-can-eat buffets! And, even after a full meal, it may be why you notice you can't resist grabbing more snacks out of the snack bowls on the table.

Other influences on how much we eat include the size of the serving we are given, and the presence of others. When there are more people around versus when we are eating solo, we don't necessarily eat more or less food, but our eating habits are accentuated.


Happy eating!

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FUN FACT: We crave carbs because they temporarily raise our level of serotonin, a mood-boosting neurotransmitter. This can reduce depression and stress!

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