Boris Johnson has promised to halt hikes on so-called “sin taxes”, which include levies on tobacco, alcohol and sugar.
He said if elected leader he will review the effectiveness of such taxes on encouraging people to live a healthy lifestyle.
“The recent proposal for a tax on milkshakes seems to me to clobber those who can least afford it,” he said.
“If we want people to lose weight and live healthier lifestyles, we should encourage people to walk, cycle and generally do more exercise.”
He added: “Rather than just taxing people more, we should look at how effective the so-called 'sin taxes' really are, and if they actually change behaviour.”
Mr Johnson’s campaign team cited taxes on products high in salt, fat and sugar as worthy of review.
However it has not confirmed whether taxes on cigarettes and alcohol would be reconsidered.
A sugar tax on soft drinks was introduced in April last year, and health organisations have pushed for the government to go further.
England’s chief medical officer has been considering a tax on all unhealthy foods to discourage parents buying junk food for their children.
Cancer Research UK chief executive Michelle Mitchell said such taxes have proven to have a “positive effect” across the globe.
“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,” she said.
“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.”