Tighter restrictions on TV adverts for junk food should not be considered until the recently introduced ban has been evaluated, the government says.
Concern about children's health prompted the ad ban
Peers have debated a bill calling for the ban, which began in April, to be widened to include adverts aimed at children before the 9pm watershed.
Baroness Thornton said the current ban was "inadequate given the scale and urgency of this problem".
But Lord Evans said time was needed to allow the ban to "bed in".
Under Ofcom rules introduced in April, adverts for food and drinks high in fat, salt or sugar cannot be broadcast around shows aimed at children under nine.
From 1 January 2008 the restrictions will be extended to TV shows aimed at children up to 15 years, as well as adult programmes watched by a large number of children.
Dedicated children's TV channels are allowed to phase in the restrictions affecting four to nine-year-olds from 1 April, but must have the full ban in place by 1 January 2009.
Labour peer Baroness Thornton, speaking during debate on her Television Advertising (Food) Bill, said: "All the good work of schools and the efforts of parents are being undermined by the torrent of advertising for less healthy food."
Her bill would end TV advertising before 9pm for foods high in fat, salt and sugar.
It would restrict advertising of food ranges which included items high in fat, salt and sugar (HFSS) before 9pm and prevent the sponsorship of pre-watershed programmes by such products.
"It would cover not only HFSS foods but deal with manufacturers, producers and brands of these foods," she said of her bill, which has the support of more than 100 peers, 233 MPs, as well as "huge" public support.
Lord Evans said it was a useful contribution to the issue of advertising, but said: "It is only right that we allow time for the (advertising) changes to bed in before evaluating their impact.
"If these measures fail to produce a change in the nature and balance of food promotion to children, we will take further action to implement a clearly defined framework for regulation in this area."
The bill was opposed by Tory Baroness Buscombe, chief executive of the Advertising Association, which represents ad agencies and clients, who said: "If a ban on the advertising of foods high in fat, sugar and salt solved the problem of obesity in Britain, how simple life would be.
"Advertising is an easy target but advertising bans have unintended consequences and won't tackle the root causes of the problem of obesity."
Tory former advertising industry executive Lord Naseby said no changes should be made until the current ban has had some time to be monitored.
Crossbencher Lord Krebs, former chairman of the Food Standards Agency, said he supported the bill.
"It has a sound scientific basis and it will make a difference to the health of the nation," he said.