Eating better might well be the best way to trim our waistlines, but it’s also hitting the wallet hard.

According to a new analysis by the Overseas Development Institute, the cost of fruit and vegetables in Brazil, China, South Korea and Mexico has risen by up to 91 percent between 1990 and 2012, a price hike higher than any other food group.

In comparison, the cost of some processed foods like cakes and cookies has dropped by 20 percent. 

“It's quite surprising since horticulture is technically advanced in most countries, while modern retail chains seemingly excel in getting fresh produce promptly to customers,” explains co-author Steve Wiggins.

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The trend isn’t specific to these developing countries: In the U.K., the price of ice cream dropped by half in the same period, while the cost of fresh green vegetables tripled.

A 2014 study out of American University in Washington, D.C., found that fruit and vegetable prices have risen 17 percent between 1997 and 2003. The researchers also looked at children up to age 5 living in impoverished families and compared their BMIs to food price data. Their findings: As prices for fresh produce rose, so did the average BMI relative to that of children in areas where fruits and vegetables cost less.

“I would love to see an experiment where we introduce an additional 15 percent tax on unhealthy foods, and spend all of the proceeds subsidising fruit and vegetables,” suggests Wiggins. “This would probably provide a subsidy of 30 percent for fruit and vegetables. Then we can monitor changes to diets and incidence of diet-related disease.”

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Last January, Mexico did just that, introducing taxes on sugary drinks and energy-dense food in a bid to halt its rising obesity rate. Wiggins said his team are watching the results closely, given Mexico’s high rate of type 2 diabetes.

Governments and health organizations around the world are spending huge sums on campaigns urging people to eat healthily — but as long as the less healthy options are cheaper, fresh produce remains a tough sell. But if new taxes do work to help bring healthy foods closer to parity, the effects could be enormous.

"A 2009 simulation study in the U.K. concluded that taxing unhealthy foods and subsidising fruit and veg would prevent 3,400 premature deaths, plus reduce the occurrence of diet-related diseases,” he says. “That's twice the number of people who die on the roads every year.