He believes many children watch TV shows such as The X-Factor, during which food and soft drink ads are permitted because most viewers are adults. He wants this loophole in the code, introduced by Ofcom in April, to be closed.
Speaking in the House of Commons on Wednesday, Johnson said that the Government had already taken the move to ban the advertising of unhealthy foods during children's TV programmes, but was "determined to go further" if evidence supported it.
Johnson's department will consider tougher rules as it draws up the Government's response to the Foresight report, published on Wednesday, which warned 60 per cent of men, 50 per cent of women and 25 per cent of children will be clinically obese by 2050.
The ad industry will now be consulted by the Department of Health, and will argue that the recent changes should be given more time to bed in.
Baroness Peta Buscombe, the chief executive of the Advertising Association, said: "We hope the Government will not pre-empt its 2007 review of food and soft drinks advertising. The future solution must be better self-regulation from the ad industry, not restrictive legislation."