There are typical reasons to be famished—and some worrisome causes. Here’s what you need to know.

Your stomach growls, you feel shaky, and you may feel on edge. You know this sensation all too well: You're starving, and it's time to eat. Hunger, by definition, is a physiological need for nutrients to provide fuel for your body, notes Risa Groux, CN, a functional nutritionist. "Just like a car needs gas to function, our bodies require food to create energy to survive and thrive. Once the tank is empty, the body needs replenishment," she explains.

From a biological standpoint, our bodies produce a hormone called ghrelin in our stomachs to signal the brain that the body needs food. While ghrelin increases before meals and drops after eating, leptin—another hormone made in fat cells—informs the brain that it has adequate energy and no need to consume any other food.

However, sometimes this process doesn't go exactly as planned. In fact, you could eat more than you need and still wonder, 'Why am I always hungry?' There are many different reasons why you might be frequently hungry—including some typical hunger causes as well as some worrisome ones. In this 101 guide, we chatted with experts to better understand hunger and the science behind it.

Typical Reasons to Be Hungry

As Groux put it, food is fuel, and our body needs it. And because our bodies are smart and complex, it will let us know when to enjoy a meal. Keep reading for details on common reasons why you may be hungry.

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1 You haven't eaten in a while. 

The most obvious reason your tummy is encouraging you to feed it? You haven't had food in a while! "A lack of food over time causes the body to become hungry, which includes discomfort in the midsection, and a feeling of weakness from lack of nutrition," explains Lauren Minchen, MPH, RDN, CDN, a nutrition consultant for Freshbit

If you notice you feel sluggish or tired when you haven't eaten, that's your body's natural response to preserving energy. According to Minchen, the length of time it takes for someone to feel the discomfort due to hunger can vary, as it depends on several factors. Generally, people can begin to feel hungry three to five hours after they last ate, but it can be longer if they previously consumed a substantial meal.

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2 You just worked out. 

Following an intense run or boot camp class, you count down the minutes until you can replenish yourself with a yummy snack or meal. Exercise, particularly a strenuous or cardio-filled physical activity, uses calories and nutrients to adequately fuel our bodies, which can lead to hunger. 

Minchen also notes that the breakdown of muscles during exercise creates a desire for food. "Training our muscle tissue and breaking it down to stimulate the building of stronger muscle tissue triggers a greater need for protein, carbs, and fats in that rebuilding process," she says. "Without these valuable macronutrients after training, our muscles won't become stronger and more resilient."

3 You didn't sleep well last night.

Believe it or not, not getting enough shut-eye can cause you to feel hungry. According to Kathleen Winston, PhD, RN, from the University of Phoenix, these two may not seem connected, but sleep is essential for appetite control. How does that work, you ask? While we are in dreamland, our brains and immune systems are strengthened, regulating the hunger hormone ghrelin. For those who don't regularly get enough rest, this hormone is higher, creating increased appetite, according to Winston. 

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4 You're not eating enough protein, fat, and fiber.

In addition to going long periods without a meal, not eating the right foods can also create those hunger pangs. Groux points out that we all need a diet that's balanced with adequate amounts of protein, fat, and fiber in order to feel satisfied. "Protein regulates ghrelin and leptin, helping us to feel full," she explains. "Quality fat helps with the production of leptin to signal that fullness and slow down our digestion."

"A high fiber intake ignites the production of short-chain fatty acids, which causes the body to feel satiated, along with creating a diversity of good gut bacteria in the microbiome," she adds. "Soluble fiber, or foods that dissolve in water, tend to decrease appetite and create a feeling of fullness."

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5 You are pregnant or breastfeeding.

Minchen notes that during pregnancy, the body's caloric and macronutrient demand increases in order to provide proper fuel for fetal growth. "These calories and macronutrients directly fuel the development and growth of the fetal brain, and skeletal, muscle, and fat tissue for a healthy baby," she shares.

Additionally, breastfeeding places an enormous demand on a woman's body, and can make her feel hungry and thirsty. Generally speaking, Minchen says pregnancy requires an additional 300 calories a day, while breastfeeding can require between 500 to 1,000 extra calories daily.

Worrisome Reasons to Be Hungry

There are some medical conditions, both physical and mental, that can create an ongoing sensation of hunger. If you're experiencing any of these symptoms, book an appointment with your doctor to answer the 'Why am I always hungry?' question and hopefully find some solutions.

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1 You have a medical condition. 

Hyperthyroidism is a condition in which more hormones are present in the body than needed. According to Winston, this can lead to excessive hunger. Other medical culprits that can cause hunger include diabetes, a parasite infection in the intestinal tract, and hypoglycemia. 

As Groux notes, fluctuations in blood sugar levels is a prevalent cause of excessive or perpetual hunger. "When blood sugar is elevated, or diabetes is present, appetite tends to increase, as does thirst," she says. "This happens because glucose cannot penetrate the cells, and the body rids it through urine. When blood sugars are depleted and hypoglycemia is present, the body will crave food to help regulate blood sugar levels."

2 Your hormones are out of whack. 

After a night of heavy drinking, do you crave pizza or another carb-heavy food? This may seem like a normal response, but it's actually a signal that your hormones are out of whack. As Groux explains, booze inhibits the production of leptin—the fullness hormone. "Additionally, greater alcohol consumption can diminish the part of the brain responsible for self-control; therefore, people tend to eat more when drinking alcohol than when not," she says.

Also, when you are going through a stressful time, you may turn to sweets or other comfort foods to cope. This is another hormonal consideration since cortisol is a hormone produced on the adrenal glands that increases with chronic stress. "Cortisol can promote food cravings and increased appetite," Groux adds.

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3 You have a disordered eating pattern.

In extreme cases, eating disorders such as anorexia, bulimia, or other body dysmorphia conditions can result in abnormal hunger patterns. Those who have these conditions tend to severely restrict essential calories and other nutrients, creating a growing sense of hunger, Minchen points out.

Then, their hunger can manifest in the breakdown of essential tasks and tissue in the body. "Skin breakdown, hair loss, constipation, rapid heart rate, and fatigue are some of the early signs of the body's breakdown as a result of chronic hunger and restriction," Minchen warns.