Gigi Hadid has revealed that her weight fluctuations are caused by Hashimoto's disease.

The 22-year-old model has taken to her Twitter account to hit back at body shamers who have slammed her for being too skinny, explaining she has done nothing to lose weight other than get the condition - which sees antibodies directed against the thyroid gland to cause chronic inflammation - under control.

In a series of passionate tweets, Gigi explained: ''For those of you so determined to come up w 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.

''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 ... I was also part of a holistic medical trial that helped my thyroid levels balance out.

''Although stress & excessive travel can also affect the body, I have always eaten the same, my body just handles it differently now that my health is better. I may be ''too skinny'' for u, honestly this skinny isn't what I want to be, but I feel healthier internally and (cont)

''(cont) am still learning and growing with my body everyday, as everyone is. (sic)''

The American model - who is dating Zayn Malik - insisted she will not make any further comment about her body, and has instead called on her social media followers to use the platform in a more positive, empathetic way.

Gigi also rubbished speculation that her slim figure is the result of drug use.

She said: ''I will not further explain the way my body looks, just as anyone, with a body type that doesnt suit ur ''beauty'' expectation, shouldnt have to. Not to judge others, but drugs are not my thing, stop putting me in that box just because u dont understand the way my body has matured.

''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. (sic)''