Abdullah Elshamy, on hunger strike in notorious Tora prison, is one of at least 16,000 held since Morsi's overthrow last year

An al-Jazeera journalist imprisoned in Egypt has lost over a third of his body weight after spending more than 100 days on hunger strike in one of Cairo's most notorious jails, claims his family.

Photographs released by the broadcaster on Monday showed 26-year-old Abdullah Elshamy during a rare court appearance as he waited to learn whether his pre-trial detention would be extended by a further 45 days.

Elshamy has been held without charge in Egyptian custody for 265 days, and on hunger strike for 103 days. The physical toll wrought by imprisonment and fasting were plainly apparent during his court appearance on Saturday.

In the prisoners' cage, Elshamy was pale and gaunt – in custody, his weight has dropped from 108kg to 68kg, according to measurements taken by his family, who were permitted to bring measuring scales on a recent prison visit.

The journalist is one of at least 16,000 people detained in the months since Egypt's military overthrew former president Mohamed Morsi in July last year.

Elshamy was arrested last August as he left the site of the Rabaa el Adaweya pro-Morsi camp, which had been forcibly cleared by police. He had been covering the sit-in for al-Jazeera's Arabic channel.

Shouting to journalists in the court, Elshamy described his conditions in Cairo's Tora prison as a "pit hole" not fit for animals, and said that his appeals for release have been denied, despite his ability to prove that he had been at the protest camp in a professional capacity.

"Bring me to trial, to charge me and prove me guilty, if they have any evidence against me," he shouted.

Unlike his three al-Jazeera English colleagues, Peter Greste, Mohamed Fahmy and Baher Mohamed, whose trial on terrorism charges has been widely covered, Elshamy has yet to be formally charged. Instead, he has appeared at bi-monthly court hearings to learn whether his legal detention period of 45 days will be renewed.

Preliminary accusations against him range from vandalism to harming national security, charges that are routinely levelled at the thousands arrested in an aggressive state-led crackdown that followed Morsi's overthrow.

"There hasn't been any serious hearing so far," said his brother Mosa'ab, an award-winning independent photojournalist.

Elshamy reported from the Rabaa el Adaweya encampment throughout August. As police moved in to disperse the site on 14 August, killing at least 600 people, he, Mosa'ab, and a third brother had stayed to document the carnage. Elshamy was arrested at a military checkpoint that evening as he left the burning square, according to his wife, who says she was with him at the time.

Since Elshamy was one of hundreds detained that day, his family do not believe his arrest was initially linked to his status as a journalist for the domestically unpopular al-Jazeera network. They do, however, believe this might explain why Elshamy remains in custody while other batches of detainees have been quietly released, midway through their detention periods.

The Qatari-owned al-Jazeera network has faced mounting pressure from the Egyptian authorities since Morsi was deposed in a military takeover on 3 July. Its Arabic channel is one of the few remaining channels perceived as sympathetic to the Muslim Brotherhood.

As Elshamy's detention continues, so has his work, according to his family. Although he has grown weak from the hunger strike, he is using his time in prison to document the stories of his cellmates, ranging from Muslim Brotherhood leaders to street vendors who sold tea at the Rabaa el Adaweya encampment.

"Before his hunger strike, he would ask for books and paper more than food and water," says Mosa'ab. "It's what keeps him alive."