$1.50. That's about how much extra it costs per person to eat a healthier diet full of vegetables and lean protein every day, according to a holistic new study from Harvard.

"People often say that healthier foods are more expensive, and that such costs strongly limit better diet habits," Mayuree Rao of the Harvard School of Public Health tells New Scientist. "But, until now, the scientific evidence for this idea has not been systematically evaluated, nor have the actual differences in cost been characterized."

Countless other studies support the theory that low income is closely tied to lower-quality, processed foods, leading to a range of health problems that include vitamin deficiency and higher obesity rates. The hassles of eating healthy shouldn't be dismissed either. Sometimes after a long day at work, it's easier to pop a frozen pizza into the oven than it is to chop up a kale salad your kids might throw a fit over.

Taking a look at 27 studies from 10 high-income countries — most of the studies focused on the U.S. — Rao and her team compared healthy and less-healthy options you might find in the grocery aisle, using both price per serving and price per 200 calories to make an assessment. One study, for example, pitted whole-grain bread against cheaper and less nutrient-dense white bread.

On average, they discovered, it costs $1.48 more per day to eat healthier.

But while that might not sound like much to many people, for low-income families "an extra $1.50 daily is quite a lot," Rao says. "It translates to about $550 more per year for one person, and that could be a real barrier to healthy eating."

For a family of four that works out to an additional $2,200 a year.

America does appear to be proactively making healthier lifestyle choices: The latest CDC findings indicate that childhood obesity rates are falling in many states.

Still, there are ways the government can help, namely by subsidizing healthy foods while taxing unhealthier options, like sugar-rich beverages. "These are evidence-based ways to address the price imbalance and nudge people towards a healthier diet," adds Rao. "These are strategies our policymakers should be looking at."