The Briton, 39, who was born in Somalia, added that his name had been changed to Mohamed Farah by Hussein Abdi Kahin in the fake travel documents used to fly him to Britain by a woman he had never met before.
Once he arrived in the UK, the woman took him to her home in Hounslow, west London, and tore up a piece of paper containing his relatives’ contact details. Her family didn’t allow him to go to school until he was 12 years old.
“For years I just kept blocking it, but you can only block it for so long,” he said in the BBC documentary, which will air this week.
“A lot of times I would just lock myself in the bathroom and cry. The only thing I could do to get out of this (living situation) was get out and run.”
His physical education teacher Alan Watkinson contacted social services and helped him find a foster home in the Somali community after Farah told him what he was going through.
“I felt like a lot of things were lifted off my shoulders, and I felt like me. Then Mo came out — the real Mo,” Farah said.
“I had no idea there were so many people going through exactly the same thing as me. It just shows how lucky I’ve been.
“What really saved me, what made me different, was that I could run.”
He said his elite track career could be over in May after finishing second in the London 10,000m race and being banned from this month’s World Championships.
Farah, who completed the doubles of the 5,000 and 10,000 meters at the 2012 and 2016 Olympics, will, however, run a marathon for the first time since 2019 when he competes in the London Marathon in October.