You’re standing in line at the deli when you overhear the girl behind you talking to her friend:“Ugh, I’m only eating lettuce and peas. I got so fat over Christmas.”You turn around to find that she’s a tiny little size two bombshell and as you take your delicious turkey and cheese melt, you shoot eye daggers of hatred her way.Sadly, you’ve seen girls like her before. (You may even have been that girl before.) “I think most women who fat talk are thin or healthy,” says body image researcher and Northwestern University professor, Renee Engeln-Maddox, Ph.D.But before you cast your wrath on them, take a minute to wonder why they do it.QUIZ: Do You Fat Talk ? Find Out for a Better Body Image“I think most thin women, when they say they feel fat, they do feel fat,” says Engeln-Maddox. “Part of it is to recognize that feeling fat comes and goes in different contexts.” Even svelte celebrities can feel fat when standing next to ultra-skinny peers.In Cosmopolitan UK’s January 2012 issue, Katherine Heigl, the gorgeous, leggy blond you might remember from “Grey’s Anatomy” or “Knocked Up,” had a rather baffling body-bashing moment. Describing her experience filming “New Year’s Eve,” Heigl said of her co-stars, “I was 20 pounds heavier and wanted to look like those girls with fantastically beautiful bodies like Jennifer Aniston or Jessica Alba, but I just couldn’t lose the weight.”Wait, Katherine Heigl doesn’t already believe she has a fantastically beautiful body?In a culture that glorifies women like Aniston or Alba, who spend upwards of two hours a day at the gym, perhaps Heigl doesn’t feel so hot when standing next to them. “Unrealistic ideals make even thin individuals feel like they’re not physically perfect,” says Denise Martz, psychology professor at Appalachian State University.It’s the comparison, or the context, that makes thin women feel fat. “You might fat talk when you feel self-conscious on the beach or if you just looked at a magazine,” says Engeln-Maddox. “That’s really different than being fat.”When faced with the total hopelessness of looking like an airbrushed cover girl (we assure you, the cover girls don’t even look like that), fat talk can be a way to express negative feelings. “I think the primary reason for fat talk is it’s an attempt to feel better,” says Engeln-Maddox, “to elicit support and empathy.”In other words, Heigl isn’t saying that she’s actually overweight—she’s expressing that she feels more self-conscious or inferior and a little less beautiful than she might in another context. She’s feeling emotional distress.RESEARCH: Thin Women Fat TalkThat calls for some empathy. “If you said, I feel really depressed today, nobody would say, oh you’re just saying that because you want me to say you’re not depressed,” Engeln-Maddox points out. Don’t assume fat talkers are fishing for compliments either. The habit may have more to do with a blue mood than vanity and according to Engeln-Maddox, fat talkers deserve the same sensitivity we’d give someone who feels depressed. “Body image is really tied to mood,” she explains.One University of Florida study, presented at the Association for Psychological Science’s 2011 convention, looked at why women say they fat talk. Many cited guilt, insecurity, negative self-comparison or fear of bodily exposure.QUIZ: How’s Your Self-Esteem? Physical reasons, like bloating, feeling full, or not fitting in clothes, were also common.That makes sense, according to YouBeauty Nutrition Advisor, Kristin Kirkpatrick, RD. “The stomach can bloat rather easily, especially with water or too much sodium,” she says. (Not to mention PMS.) Thin women may be more likely to notice minor bloating or physical changes since they tend to wear form-fitting clothes that exacerbate the feeling.“Overweight women tend to wear much looser clothing,” says Kirkpatrick. “The big joke about wearing elastic pants to Thanksgiving is true. If you wear something that has a button or something form-fitting, you will stop dinner pretty quickly because you feel uncomfortable. With looser clothes, you’re less likely to realize you’re full.”Still, many thin women start fat talking before they take a single bite, like it’s an extension of ‘hello’ when two women sit down to lunch together.“Some women do it because it’s a social ritual,” says Engeln-Maddox. “Because if you opt out, you’ll look snotty.” That fear can be exacerbated for women who are thin but want to acknowledge vulnerability or imperfection—to appear humble in front of their friends. “People are socialized to be humble,” says Martz. “Some fat talk is a way of acknowledging physical flaws.”MORE: Ditch the Fat Talk HabitThe camaraderie we feel when we realize we all have imperfections or insecurities can be an important building block for female friendships, even if fat talk isn’t the best way to build that trust.Of course, that only works when everyone in earshot is skinny, otherwise putting yourself down just makes other people feel worse. As one woman told Engeln-Maddox during a study, “If you’re fat, then I’m humongous!” (And here come the eye daggers again.)No amount of understanding can make the sound of fat talk any sweeter, but hey, we’ve all had bad days, we’ve all felt a little insecure, and no matter our size, we can agree that we all deserve to feel better about our bodies.