Some posts will be hidden from under-18s while others promoting "miraculous" weight loss products will be removed.

There have been increasing concerns over the impact promoting diet products can have on young people.

Actor Jameela Jamil said the move was a "huge win" in the fight against the diet and detox industry.

The Good Place actor had taken major celebrities to task over their endorsement of "detox" teas, lollipops, and supplements, many of which have a simple laxative effect. She has publicly criticised influencers including the Kardashians and singer Cardi B.

Many of her followers celebrated the news - with some asking if they could activate the same block if they were over 18.

How do the new changes work?

Unrealistic "get thin quick" promotions will be taken down and young people will be restricted from viewing some posts related to dieting and cosmetic surgery if they have an incentive to buy.

Users will be able to report posts they think violate the policy, and Instagram will review them to decide whether they need to be restricted or taken down.

The changes will also apply to Facebook, which owns Instagram.

But the restrictions will only apply to users that Instagram knows are younger than 18 - and the app does not ask users for their date of birth when they sign up.

Instead, users signing up are simply asked to tick a box declaring themselves over 18 or not. If they sign up using a Facebook account, their age information is pulled from their Facebook profile - which is also not usually verified.

Why is Instagram changing?

There has been increasing concern over the effect the cosmetic and diet industry is having on people through the promotion of unrealistic goals.

In February, the medical director of National Health Service England, Stephen Powis, called for a ban on celebrity-endorsed social media ads promoting weight loss aids, stating that products were having a damaging effect on the physical and mental health of young people.

A BBC investigation found children swapping graphic images of weight loss and advice on how to make their illnesses more extreme were common on the platform.

Ms Jamil, who founded the I Weigh movement as a reaction against content promoting weight loss products and unhealthy lifestyles, welcomed the changes.

"Facebook and Instagram taking a stand to protect the physical and mental health of people online sends an important message out to the world," she said.

"I'm thrilled to have been able to work towards this with them, alongside a host of other experts who shed light on the danger of these products."

Emma Collins, Instagram's public policy manager said: "We want Instagram to be a positive place for everyone that uses it and this policy is part of our ongoing work to reduce the pressure that people can sometimes feel as a result of social media."

Advice had been sought from experts in the field of social media policy, she added.