The British Heart Foundation (BHF) says two thirds of people would like to eat more healthily, but 42% said they cannot because of cost.
Soaring food prices have seen grocery bills rise almost twice as fast as rent in the last five years, the BHF said, leaving nearly 40% of people admitting they have to sacrifice health for cost when it comes to the weekly shop.
The survey said people on the lowest incomes were hit hardest, with three quarters of people earning less than £10,000 a year saying they struggled to afford five daily portions of fruit and vegetables.
Victoria Taylor, senior dietitian at the BHF, said: "With the increasing cost of a weekly shopping basket it's a real concern that despite people's best intentions they're struggling to eat healthily.
"But there are ways you can make healthy home-cooking affordable, so that the rising price of your food shop doesn't need to come at a cost to your heart health."