Letters have gone out to agencies and TV stations advising them of the new regulations.
The main stipulation for fast food companies is that they refrain from advertising around programmes where young children constitute four per cent or more of the audience.
The 4As has been appointed as a watchdog to ensure the regulations are adhered to.
The health minister instigated a move towards tighter control of fast food advertising in May last year, when a national newspaper quoted him as suggesting that fast food was as unhealthy as alcohol and tobacco.