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What is Hashimoto's disease, the weight-related condition Gigi Hadid suffers from?

Gigi Hadid has hit back at body shamers who have commented on her changing body shape.

In a series of passionate tweets, the 22-year-old model responded to trolls who have commented on her fluctuating weight, explaining that the changes are due, in part, to being diagnosed with Hashimoto’s disease.

“For those of you so determined to come up [with] why my body has changed over the years, you may not know that when I started @ 17 I was not yet diagnosed w/Hashimoto’s disease; those of u who called me “too big for the industry” were seeing inflammation & water retention due to that,” she wrote.

Gigi Hadid has hit back at body shamers. (Photo: Getty Images)

“Over the last few years I’ve been properly medicated to help symptoms including those, as well as extreme fatigue, metabolism issues, body’s ability to retain heat, etc…,” said the model, who is dating former One Direction star Zayn Malik. “I was also part of a holistic medical trial that helped my thyroid levels balance out.”

Hadid also said that whereas stress and excessive travel, which are big parts of a career in modeling, can affect the body, she has always eaten the same.

“I may be “too skinny” for you, honestly this skinny isn’t what I want to be…” she said. “I will not further explain the way my body looks…stop putting me in that box just because u dont understand the way my body has matured,” she wrote.

Hadid concluded her statement with a call to others to stop the body shaming.

“Please, as social media users & human beings in general, learn to have more empathy for others and know that you never really know the whole story. Use your energy to lift those that you admire rather than be cruel to those u don’t.

Unsurprisingly, Hadid’s followers were quick to step in and offer support, including some of the model’s celebrity friends.

Replying to Hadid’s tweet, Ruby Rose wrote: “Sorry you too have to explain something so ridiculous to people. Love to you. Love to the people who try to tear down others also because they are just people who haven’t had the spiritual growth that needs to occur to love and accept one another.”

Chrissy Teigen, who has faced criticism about her body,  wrote: “Alternate tweet: “f**k off”

According to the National Health Services,  Hashimoto’s disease is an autoimmune disorder caused by the immune system attacking the thyroid gland, making it swell and damaging it.

The site says that people who suffer with it will have symptoms of an underactive thyroid gland, including fatigue, weight gain, constipation, dry skin, and depression.

In some cases, the swollen thyroid may also cause a goiter (lump) to form in the throat.

But Thyroid UK says that Hashimoto’s disease can manifest itself in many ways, causing different symptoms. “The thing to understand about Hashimoto’s disease is that it is basically a variant of hypothyroidism, caused specifically by autoimmunity; the thyroid gets infiltrated by white cells and slowly loses its function; it usually enlarges but may not, and may start with an over-active phase before becoming under-active,” according to the site.

Although it is not known what causes Hashimoto’s disease, it is believed it does sometimes run in families.

Gigi Hadid has Hashimoto’s thyroiditis, an auto immune disease (Photo: Getty Images)

Hashimoto’s thyroiditis cannot be cured, but the symptoms are often easily treated with a thyroid hormone-replacement medication, which is usually taken for life.

Surgery is needed only in rare cases, if, for example, a goiter is particularly painful or uncomfortable.

Hadid first revealed she was suffering from the condition in 2016. “My metabolism actually changed like crazy this year,” she told Elle Magazine. “I have Hashimoto’s disease.

“It’s a thyroid disease, and it’s now been two years since taking the medication for it, so for the Victoria Secret show I didn’t want to lose any more weight, I just want to have muscles in the right place, and if my butt can get a little perkier, then that’s good.”

She revealed that her mom taught her a trick to help her cope when people are cruel about her body.

“Literally, screaming into a pillow helps,” she said. “One time I was on set for a beach shoot, and my mum said, ‘Go scream into the ocean. It relieves the tension.'”

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