How common is it for celebrities to get slammed for their weight? So much that it wasn’t surprising when Fox News host Chris Wallace commented (and later apologised) that Kelly Clarkson “could stay off the deep-dish pizza for a little while.” Or when TMZ posted a picture of bikini-clad Selena Gomez on a Mexican beach and wrote “things are getting thick down in Mexico.” Or when Twitter trolls told Pink, dressed up to go to a gala honouring cancer survivors, that she looked fat in her dress.

What was unusual about those nasty critiques? That the stars fought back. Immediately.

Thanks to the age of social media, celebs have that option — such as Pink shutting down her critics on Twitter, or Selena Gomez taking to Instagram to do the same. While it’s commonly accepted that ignoring the haters will make them go away, experts say there’s more benefit for stars, more than anyone, to speak up: because it’s already psychologically harmful for everyday people to witness celebrities get fat-shamed, and striking back against the bullies can only help.

Obviously, experts say, everyone recognises that eating healthy food is important. But when people see celebrities they admire getting criticised for being “fat” despite actually being healthy, it can have an impact on how they see themselves. Particularly troubling is the potential effect on younger women — they’re not only the ones more likely to look at celebrity headlines and follow Hollywood news, but are also a demographic more prone to develop eating disorders.

“We need celebrities to change the culture,” said Marjorie Nolan Cohn, the national spokesperson of the Academy of Nutrition and Dietetics. “It’s sad but true — this is who we look up to as a society. If they’re not saying anything, [sending] a positive message is going to be a much harder and longer road.”

Another psychological issue: readers and fans seeing people who look like movie stars (men and women) criticised, and feel even worse about their own bodies. Clarkson, speaking on Ellen DeGeneres’s talk show, talked about the dangers of that line of thinking.

“I think what hurts my feelings for people is that I’ll have a meet-and-greet after the show and a girl who’s, like, bigger than me will be in the meet-and-greet and be like, ‘Wow, if they think you’re big, I must be so fat to them,’” the singer said.

Luckily, certain stars don’t wait to fire back. Pink posted a long note to Twitter: “I am perfectly fine, perfectly happy and my healthy, voluptuous and crazy strong body is having some much deserved time off,” she wrote, adding “my hubby says ‘it’s just more to love baby.’”

The clip of Clarkson went viral as she told DeGeneres she brushes off the critical comments, saying “Sometimes I’m more fit and I get into kickboxing hardcore. And then sometimes I don’t, and I’m like ... I’d rather have wine.”

Selena Gomez, meanwhile, posted a bathing suit picture of her own to Instagram with the caption “I love being happy with me yall” and “#theresmoretolove.”

Cassey Ho, a YouTube fitness star, took her response to the extreme this week, creating a video where she Photoshopped her body with all the cruel comments people have made about her appearance.

Psychologists agree that celebrities defending themselves against the absurd comments can have an impact on pop culture consumers. Nancy Mramor, a psychologist specialising in the social effects of media, agrees with the many publications that praised Pink’s response — while celebrities don’t have to fight back, if they’re going to, they should use the singer’s methods to say “I’m strong, I’m healthy and I’m happy with me.”

“The reason that women have become obsessed with their bodies is because of celebrities. It started with models and actresses who are physically perfect or airbrushed into being perfect, and people aspire to be like them,” Mramor said.

Now, she said: “We have some powerful role models saying they’re not physically perfect, don’t want to be, don’t aspire to be and don’t judge themselves because they’re not.”

In the end, it can go a long way to battle other messages that routinely stream into the media, such as whenever a starlet’s “diet plan” is revealed. Cohn, the nutritionist, says that her clients often bring her things they find on the internet about, say, Jennifer Aniston’s daily nutrition and wonder if they should copy it. (The answer is almost always no.)

The most important thing, Cohn said, is for any star to reiterate a message to a broader audience: “This is who I am and I like it this way and it works for me. I’m healthy without being perfect.”