Boris Johnson has promised to stop increases on so-called "sin taxes" - which includes levies on sugar, alcohol and tobacco - should he become the next prime minister.
The leadership frontrunner said he would review the effectiveness of such taxes to see whether they unfairly target low income households.
He also pledged not to introduce new sin taxes until the review had been completed.
Speaking on Wednesday, Mr Johnson said: "What I want to see is evidence, actual evidence, that new taxes on this or that item of food - and taxes which fall disproportionately on poorer families actually stop people from being so fat."
His campaign team cited taxes on products high in salt, fat and sugar for example, but it is unclear whether the review would extend to alcohol and tobacco taxation.
The announcement comes as Health Secretary Matt Hancock - a prominent backer of Mr Johnson - is to recommend extending the sugar tax to milkshakes.
Furthermore, Mr Johnson's announcement comes as Cancer Research UK said obesity causes more cases of some cancers than cigarettes.
Responding to the comments, leadership race competitor Jeremy Hunt said he was "totally confused" by Mr Johnson's policy.
He referred to Matt Hancock's backing of the taxes and Mr Johnson as a point where the campaign frontrunner lacks "consistency".
During his time of Mayor of London in 2016, Mr Johnson introduced a 10p levy on added-sugar soft drinks sold in City Hall, saying that tackling obesity was "one of the biggest" health challenges.
Medical experts have hailed the effect of sin taxes on unhealthy foods, saying they discourage parents from buying the produces.
Professor Dame Sally Davies, England's chief medical officer, said she hopes to promote healthy food sales, possibly by taxing unhealthy foods more.
A report by Dame Sally is due in September and was commissioned by Mr Hancock.
The sugar tax was introduced in April last year and has been celebrated by experts, including the Royal College of Paediatrics and Child Health.
Irn-Bru, Dr Pepper, Sprite, 7up, Fanta and many other soft drink brands changed their recipes to avoid being hit by the tax.
Deborah Arnott, chief executive of Action on Smoking and Health, said Mr Johnson's proposals were a "grave error".
She said: “Smoking kills more than 100,000 people in Britain each year. And the evidence from other countries is clear, when taxes stop going up, smoking rates are likely to stop going down,” she said.
“Making tobacco less affordable via taxation is considered to be the most effective means of discouraging young people from starting to smoke and helping adult smokers to quit.
“That’s why this Government and its predecessors have implemented an escalator for tobacco taxes which increases prices above inflation at every Budget.
“To move away from that policy now would be a grave error.”
Michelle Mitchell, chief executive of Cancer Research UK, praised the effectiveness of such taxes.
“They have been highly effective in bringing down smoking rates to record lows, including within deprived communities, and the Treasury’s own analysis showed the tax on sugary drinks took 90 million kg of sugar out of the nation’s diet on day one.
“Physical activity is one way to lose weight but the Government also has a big role to play if we are to significantly reduce obesity levels.
The Obesity Health Alliance’s Caroline Cerny said voluntary programmes for the food industry to cut sugar “have not had the same success” as the tax.
“The levy is supported by the public and welcomed by a wide range of health experts and is vitally needed as part of a package of measures to help create a healthier environment for everyone,” she said.