You've been told for years that the best thing to treat or prevent a urinary tract infection naturally is cranberry juice. But a new report suggests you've been lied to — by the very people who make cranberry juice.

The main piece of research substantiating the health benefits of cranberry juice was paid for by Ocean Spray, North America's foremost producer of cranberry juice, and co-authored by company scientists, Julia Belluz reported in Vox.

The research, which was published in the American Journal of Clinical Nutrition, appeared to be legit: It was double-blind, randomized, and placebo-controlled. But Vox reported that the research was likely biased in both its methodology and findings that cranberry juice not only prevents UTIs but also works to combat antibiotic resistance, which means the beverage could be used to treat UTIs in lieu of antibiotics.

Belluz reported, among other things:

"The result the researchers found was actually pretty dismal in absolute terms: Drinking cranberry juice every day for 3.2 years averted one symptomatic UTI (and remember, that means not necessarily one that's confirmed through a lab test)."

About 60 percent of women will experience a UTI in their lives — men occasionally will, too, but not nearly as often. There are active compounds in cranberries that can prevent UTIs from developing, but past studies have shown "that juice and supplements don’t have enough of this active ingredient, A-type proanthocyanidins (PACs), to prevent bacteria from sticking to the urinary tract,” according to the Cleveland Clinic.

Pen Waggener/Flickr - flickr.com

Ocean Spray's study, meanwhile, ignored as a variable the effect of sugar on urinary tract health. A cup of cranberry juice contains a little more than 30 grams of sugar, which has actually proven counterproductive in treating UTIs. A beverage containing only 100 percent cranberry juice, on the other hand, can help to prevent and treat UTIs, but it tastes nothing like the cranberry juice cocktail produced by Ocean Spray, which is only 27 percent juice.

Belluz tracked down Kevin Maki, lead author of the study and president and chief science officer at MB Clinical Research and Consulting, which conducts nutrition studies. When she asked him about how to make sense of these findings in light of other evidence, he responded that 30 percent of women never actually have a UTI, only symptoms — and the study found women with symptomatic UTIs were helped by cranberry juice.

"There are several possible explanations for this finding," Maki added. "One is that cranberry is preventing infection, and another is that cranberry compounds are having anti-inflammatory effects that prevent symptoms when a mild infection occurs."

ATTN: reached out to Ocean Spray for a comment, and we'll update this story when we hear back.

This study points to a bigger problem.

The Ocean Spray study is just the tip of the iceberg when it comes to industry-funded research with questionable findings:

• Research funded by Big Tobacco understated the risks of secondhand smoke to cardiovascular health.
• A study by the National Confectioners Association found that children who ate sugar weighed less.
• Research funded by Coca-Cola showed that physical exercise was more important than diet in fighting obesity.

Carolyn Heneghan of Food Dive wrote:

"The tenets of [the cranberry juice study] go beyond what even supporters of industry-funded research might have deemed acceptable, based on points made in a BMJ article earlier this year. They said industry-funded nutrition research had its place because the company or association's interests could align with public health. But they argued that safeguards would need to be put in place to manage use of the funds and the structure and analysis of the study itself."

Read the full article on Vox.