The brothers, who arrived in court in shackles, were questioned in turn by their defence attorneys and government lawyers as they took the stand.
Andrew Tate, 39, declared he has “never committed the crimes I’m accused of”.
Tristan Tate, 38, described his detention conditions as small and hot, with little sunlight and exercise.
“It’s beginning to grate on me because I can’t partake in helping with my defence,” he told the court, according to CBS News, the BBC’s US partner.
“It’s death by scurvy,” he said, adding that he had lost 14lb (6.3kg).
The British Embassy filed court documents asking the judge to keep the Tates in custody as the UK pursues extradition.
US government lawyers pushed back against the brothers’ claims that they had exaggerated their wealth to massage their online personas.
The federal attorneys said the Tates had access to resources that could help fund an escape and they had bragged about having multiple passports.
But Andrew Tate, a former professional kickboxer, testified that to support himself financially, he “had to go back to the boxing ring against heavier, younger opponents”, according to CBS News.
“I’ve said some stupid things, but sometimes you have to shake the internet to get noticed,” he testified about his online statements, according to CBS.
“This is the reality of the internet.
“I’m being treated like El Chapo,” he added, referring to the Mexican drug kingpin, “but I have a perfect record in the court system”.
Under questioning from his attorney, Joseph McBride, Andrew Tate denied he was a human trafficker.
The defence also called Natasha Sesay, from England, to testify in support of releasing Andrew Tate.
She described a five-year romantic relationship, saying she had had one child with him and was expecting a second.
“It’s nice having him at home,” she told the court, reports CBS.
Sesay also said that despite his online persona, Andrew Tate “has never ever been violent toward women”, according to CBS.
The UK has brought a total of 59 criminal charges against the Tates, including rape and counts relating to sex trafficking and indecent images of a child.
The British authorities filed 21 charges last year against the brothers, then 38 additional counts last month.
The combined charges involve seven accusers, UK prosecutors said.
The brothers also faced sex-trafficking charges in Romania in 2022, and were under a travel ban until they were allowed to come to the US in 2025.
“If I go to England they will lock me up,” Tristan Tate said on the stand in Miami on Thursday, “and take everything I’ve ever worked for”.
He also said the Romanian charges had “destroyed my entire life”, reports CBS.
“They took everything, even the savings accounts for their [his children’s] college funds. This case is make or break for me.”
The Tates built an influencer empire in the so-called manosphere, showcasing a lifestyle of conspicuous wealth and excess.
Andrew Tate accumulated millions of followers among an audience of primarily young men.
The White House has said President Donald Trump will not intervene in the extradition case of the brothers, who have been vocal supporters of him.
