Tessa Jowell, the culture and sport secretary, said yesterday that she was optimistic that Britain's obesity epidemic could be fought without government legislation.

Giving evidence at a Commons select health committee hearing on obesity, she argued that food manufacturers and advertisers should send out responsible messages about healthy eating. That would be a far more effective than any action by ministers or MPs.

She denied that her reluctance to act immediately was motivated by the desire to placate or reassure food industry interests.

Wary of allegations of promoting a nanny state, she has already said she is reluctant to ban food advertising on children's TV. She had, however, asked the media regulator Ofcom to re-examine the robustness of the broadcasting code on advertising to children.

She said she was awaiting a report from the Food Standards Agency on the impact of advertising on childrens eating habits. She insisted she would not act on the basis of emotion.

She blamed obesity as much on the decline in physical activity by children as on an increase in calorie intake.

"What has received less attention is the fact that activity levels have substantially reduced, including a decline in the number of children walking to school."

The committee chairman, David Hinchliffe, said too many departments acted in a contradictory way.

Ms Jowell rejected the allegation, saying she expected a Whitehall consensus could be achieved in a summer white paper on obesity. "It would be very easy, and this is always a risk in this kind of area, to do something because there appears to be a lot of public pressure, in the absence of a clear understanding of its impact."

Challenged by MPs, she refused to criticise the decision to let companies such as Cadbury's sponsor sporting activities like the Get Active campaign.

Ms Jowell, who was appointed the first public health minister five years ago, said: "Sport in this country is not in a position to turn away sponsorship that can provide facilities and equip teachers to be better at encouraging people to be physically active."

She denied that it was wrong to let companies selling high- calorie products associate themselves with sport.

She wanted children themselves to be knowledgeable about the importance of undertaking sporting activity. Food companies and advertisers were uniquely well placed to set out realistic messages about diet, she said, adding that she was optimistic about that.

"That will be a far more effective way of doing it than any message I send out."

Sport England's overriding aim now was to spread physical activity rather than promote elite sportsmen, she said.

Although some MPs accused her of taking the easy way out by concentrating on physical activity, rather than marketing, she insisted: "One causal element of obesity is the fall-off in physical activity".

She insisted that any strategy had to address both physical activity and healthy eating.

The childrens' minister, Margaret Hodge, said the government was spending £1bn on school sports facilities and teacher training.