TikTok is preventing users searching for "skinnytok" - a hashtag which critics say directs people towards content which "idolises extreme thinness."
Content associated with the hashtag includes videos showing people's work-out routines or what they eat in a day.
TikTok said it had "blocked search results for #skinnytok since it has become linked to unhealthy weight loss content."
People using the hashtag will now be redirected to mental health support resources instead.
According to the US-based National Alliance for Eating Disorders, the skinnytok hashtag has more than half a million posts associated with it.
It says the hashtag includes content such as low-calorie recipes which on the face of it appear to promote healthy lifestyle advice.
But the organisation says, in reality, it "glorifies thinness and vilifies weight gain" and "promotes disordered eating behaviours."
The trend has caused particular alarm in France, where experts have warned of how social media can push vulnerable young people towards developing eating disorders.
"The patients are completely indoctrinated -- and my 45-minute weekly consultation is no match for spending hours every day on TikTok," the nutritionist Carole Copti told the AFP news agency.
The blocking of the hashtag has been celebrated by France's digital minister, who wrote on social media that "skinnytok is over" thanks to lobbying by European politicians.
In its statement, TikTok said it regularly reviewed its safety measures to "address evolving risks".
"We continue to restrict videos from teen accounts and provide health experts and information in TikTok Search," it added.
It is not the first time TikTok has been forced to take action over content which raised body image concerns.
In March, it blocked so-called "chubby filters" - a viral tool which made people appear overweight.
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