Speaking during a debate entitled Channel 4 on Trial, Root, who is now executive vice-president and general manager of Discovery Channel in the US, said: 'The worst thing is a scared C4.'
Root likened Big Brother's hold on the channel to her own dependence on gardening programmes during her time at BBC2.
When one programme or genre dominates the schedules, a broadcaster 'has to get out of it otherwise it eats up the whole network', she said.
Root added: 'C4 has to keep everyone else relevant. The most important thing is to go forward in an optimistic, innovative way. It would be really scary if C4 starts to become a mini BBC, worrying about quotas.'
Head of BBC Vision Peter Salmon raised similar concerns.
In a pre-recorded interview, he said: 'C4 feels like a marketing proposition rather than having a critical mass centre of gravity.'
During the courtroom-style debate, chaired by Andrew Neil, C4 chief executive Andy Duncan and director of television and content Kevin Lygo defended the broadcaster's record in a troubled year in which it was rebuked by Ofcom over the Celebrity Big Brotherrace row and forced to refund participants in Richard & Judy's premium rate phone-in quiz You Say, We Pay.
Upholding C4's remit to challenge and innovate, Duncan declared: 'The channel has been permanently on trial since its launch in November 1982.'
The channel's news output and commitment to current affairs through 40 Dispatchesprogrammes a year was 'stunningly evident' of its public service ethos, he said.
Duncan said he regretted that the debate over C4's funding had overshadowed its creative contribution and that the 'barrage of negative headlines' had obscured the weight of its public service commitment.
Lygo admitted that C4 had ignored the viewers' feelings over the Celebrity Big Brotheraffair and focused too closely on the intentions of the housemates.