When you eat according to your body cues, you know that a grumbling stomach means it’s time to chow down and that feeling full will signal you to put down your fork. But what happens when your appetite has disappeared without warning?

Generally, your appetite does decrease as you age, but it’s a pretty gradual process, according to dietitian Bess Berger, R.D.N., C.D.N., owner of Nutrition by Bess. An appetite that just up and disappears, though, is a different story. “In a generally healthy person, I consider this to be a decrease below their usual appetite,” she explains. “They may not finish their typical meals or snacks.” 

So, what scared your stomach rumbles away? Here, dietitians break down five factors that can cause appetite loss, and when it’s time to see a doctor.

1. You’re Stressed Out

Unfortunate situations like a breakup or job loss can contribute to stress, anxiety, and depression, all of which can impact your desire to eat by driving up cortisol, which is like your internal alarm system that goes off when you’re in danger, according to Danielle McAvoy, M.P.H., R.D.N., a dietitian for Strong Home Gym.

Read More: 4 Unexpected Ways To Manage Stress Naturally

Sky-high cortisol basically shifts your body into survival mode, causing digestion to come to a screeching halt. “While it’s normal to feel stressed and lose your appetite once in a while, prolonged high cortisol levels can lead to many health issues,” says McAvoy. “If stress and anxiety are frequently ruining your appetite, get help managing stress.” Consider speaking to a mental health professional or finding healthy ways to cope. 

2. Your Hormones are fluctuating

Our bodies are full of hormones that fluctuate, and these ebbs and flows can certainly impact our appetite. 

People who get periods, for example, may notice their appetite levels—and cravings—increase right before their period and then taper off once it starts. “This is okay and expected; it’s our body’s readjusting with hormones,” says Berger. 

Additionally, hormone imbalances from conditions like polycystic ovary syndrome (PCOS), in which the ovaries produce an abnormal amount of androgen hormones, could also impact appetite. If you frequently experience appetite changes in addition to other symptoms like missed periods or excess body hair, consider seeing a doctor or dietitian. 

Underlying thyroid conditions are another common cause of appetite shifts since your thyroid produces hormones that regulate how quickly cells turn nutrients into energy. If your thyroid doesn’t produce enough hormones, a decrease in appetite, along with symptoms like brittle nails and hair loss, can ensue. If any of this sounds familiar, check in with your doctor.

3. You Feel Under The Weather

When you’re sick with the flu or a cold, you probably sleep a lot more and opt more for fluids like chicken noodle soup over solid foods. According to McAvoy, eating less food while you recover for a few days is likely not a big deal. However, if your appetite doesn’t return once you’re feeling otherwise normal again, you may want to check with a doctor. 

4. You’re trying out a new Diet

There’s no shortage of trendy diets out there and often these eating styles have unexpected effects on your appetite. “Many of my clients who have tried a keto diet or intermittent fasting have been surprised to find that their appetite decreased,” says McAvoy. This may be because diets low in carbs (keto is essentially carb-free) and eating patterns such as intermittent fasting (in which you eat during certain time windows) help keep blood sugar levels steady, which can reduce hunger.

Read More: 6 Types Of People Who Can Benefit Most From Intermittent Fasting

That said, some people actually experience increased hunger after depriving themselves of food for long periods of time. Feeling hungry and deprived does not make for a sustainable way of eating, so be wary of how different diets impact your appetite and reach out to a dietitian if your eating style has you feeling out of balance.

5. You OverIndulged a Day or Two Earlier

If you had an indulgent last few days (think a vacation or a holiday gathering) and ate a lot more than usual, it’s possible that you may not feel as hungry as usual as your body adjusts back towards balance, says Berger. This is especially common after eating a lot of high-fat, high-calorie meals (like anything fried).

Bottom Line

While some of the reasons our appetite wanes are pretty benign (and temporary!), appetite loss that contributes to significant unintentional weight loss (think five percent of your body weight in six to 12 months) is definitely a reason to check in with your healthcare provider. These changes, especially when combined with fatigue, changes in digestion, and increased incidence of illness, could signal trouble. Your doctor may want to conduct imaging tests or blood and urine checks to identify the culprit.