There's no simple way to explain why you could eat a burger and fries after housing the same meal that left your friends stuffed. That's because there's an infinite combination of variables that affect your appetite, according to James Greenblatt, M.D., a Massachusetts-based psychiatrist and the author of Answers to Appetite Control.
1. Your stomach is literally larger than your friends' stomachs. Regardless of your jean size or the state of your six-pack, an anatomical difference in stomach size could explain why you need to super-size your meal to feel satiated. Everyone has a unique body shape and size—and the same goes for your organs.
2. You LOL all the time. Your awesome sense of humor may ultimately stoke your appetite, according to a small study presented at the Experimental Biology Conference in Anaheim, California, in 2010. Researchers showed participants either stressful or hilarious 20-minute film clips and then measured their levels of ghrelin (the hormone that stokes your appetite) and leptin (the hormone that tells your brain you're full). People who laughed through the funny films had higher level of hungry hormones and lower levels of satiety hormones than people who watched the serious stuff. But don't stop yourself from giggling—laughter is still an awesome way to boost endorphins, particularly among people who feel too sad or stressed to eat.
3. Your diet is void of healthy bacteria. Some research suggests that prebiotics, or non-digestible fibers found in foods like chicory root, artichokes, garlic, and onion, could help suppress your appetite by altering your gut bacteria. Skimp on it, and you could find yourself hankering for seconds.
4. You always eat breakfast—but skipped it this morning. Regular breakfast eaters who forgo a morning meal get hungrier than habitual breakfast skippers, according to a 2015 Obesity study. (Good news: Research shows that skipping breakfast doesn't necessarily make you overeat at lunch.)
5. You're drunk. As any late-night pizza-eater will attest (and research can confirm): Alcohol stokes the appetite and suppresses self-control.
6. You don't eat enough protein. When you eat a hearty source of protein, like a chicken breast (25 grams of protein per 3 ounces) or Greek yogurt (18 grams of protein, depending on the brand), your body breaks the nutrient into amino acids. These guys are the building blocks that help to regulate your appetite so you know to put your fork down when you're full. Skimp on protein (i.e., eat less than about 46 grams per day, according to the Centers for Disease Control), and your food brakes might malfunction. You'll keep eating and eating and…
7. You pop antacids like it's your job. Antacids neutralize acid and inhibit the activity of digestive enzymes—two benefits if you're suffering from heartburn or indigestion. However, the drugs can inhibit your body's ability to break down even high-quality dietary protein into all-important amino acids. So it's like you ate that burger for nothing!
8. You're constantly stressed. While temporary stressors (like pre-interview jitters) may suppress your appetite on the spot, persistent stress could kick your stress hormones into overdrive, increasing your motivation to eat around the clock. Another thing: Cortisol can also stimulate intense cravings for sugar, so you'll be "hungry" for dessert although your body is physically stuffed.
9. You're a candy monster. Sugar disrupts natural appetite cues. So that bag of Skittles you ate to hold you over until dinner? It might actually make you hungrier.
10. You're getting your period. There's no doubt that sex hormones influence your appetite. Research suggests that estrogen, in particular, plays a leading role in regulating appetite (calories in) and metabolism (calories out). Right before you get your period, estrogen levels plummet—which could be the reason why you're particularly ravenous (namely for carbs, sugar, and salt) at the very end of your cycle.
11. You ate a lot of crappy carbs. Refined carbs (like cake, candy, and crackers) don't satisfy you as much as a balanced, nutritionally dense meals that contain the same number of calories. Unlike protein and high-quality fats, your body can't use refined carbs for raw materials to produce serotonin, a neurotransmitter closely linked to physical and emotional satisfaction after meals. And refined carbs tend to be low in filling fiber, unlike their whole grain counterparts. Useless!
12. You didn't work out today. Contrary to what you might think, working out doesn't automatically make you hungrier. Aerobic exercise actually decreases circulating levels of the hunger hormone ghrelin, reduces stress (which can make you eat more), and boosts your energy—so you don't feel as desperate to eat food for fuel. Skip your workout though, and you're SOL.
13. You really worked out today. While low-key cardio can help you fend off hunger pangs, getting extra activity (even if it's just walking around more than usual) can leave you low on energy and craving second helpings.
14. Your friends are super skinny. If you're taller or more muscular than your friends, you might naturally need extra calories to fuel your body. Meanwhile, you might underserve yourself to match the amount of food on your petite friends' plates — a move that may leave you craving more.
15. You ate without paying attention. Every part of your environment can affect the amount you eat and your satisfaction, from your company to your plate size and color to a restaurant's lighting, and so on. If you mindlessly ate off a small plate while gabbing to your friends at a dimly lit party, you could easily eat a meal's worth of calories without registering it as a meal. When's dinner?
This article originally appeared on Cosmopolitan.com. Minor edits have been made by the Cosmo.ph editors.