Boston (WHDH) — It's been a little over a month since all those New Year's resolutions to lose weight in 2013.

So what did you promise to do?

Eat less? Work out more?

Well, everything you might be doing – may not matter!

A surprising new report in a prestigious medical journal claims some of the most popular notions on weight loss are just plain wrong.

Think long-term dieting will keep you thin? Or that sex can help you lose weight? Or that gym class can prevent childhood obesity?

A new report in the New England Journal of Medicine tries to separate what's fact and fiction when it comes to weight loss.

Researchers analyzed existing studies to highlight what they call "myths," "presumptions" and "facts" about obesity which affects more than one-third of Americans.

"Our paper looked at a number of beliefs that are very commonly offered, both among the general public, in mass media, and even by academics and government regulators and public health advocates as things that we know to be true about obesity or weight loss but in fact, we found either in some cases were not true according to evidence available and in other cases were neither known to be true nor known to be untrue, there just wasn't enough evidence available,” said Dr. David Allison of the University of Alabama at Birmingham.

One of seven myths – that sex can burn hundreds of calories at a time. Researchers found it's closer to 21 calories.

Another myth is that big weight loss goals set you up for failure. Turns out – if you set your mind to losing more weight, you can.

Some myths are controversial.

The study said physical education won't help fight childhood obesity – and that losing weight slowly isn't necessarily better than dropping pounds quickly.

But some doctors question those findings.

"It's a lot of these small changes together is where you see long sustained weight loss, you see better health, you see improved health,” said Dr. Joey Skelton, of Wake Forest Baptist Medical Center.

Another concern was that the study was funded by corporate sponsors, which while disclosed, included Jenny Craig, Coca Cola and GlaxoSmithKline

"Where they found the best evidence for weight loss was in things like meal replacement drugs and bariatric surgery. And that brings up the whole question of conflicts of interest that the authors reported,” said Dr. Marion Nestle, a nutritionist at New York University.

Many experts do agree on some of the facts the study cites, including:

– People need to make long term changes to get results and

– Increased exercise improves health.

“We didn't want to appear to be saying that there is nothing we know now in the field of obesity and nothing we can recommend,” said Dr. Allison.

But what people really want to know is how to shed the pounds for good.

Losing weight is a combination of basic math – burning off more calories than you intake.

To lose weight, you need to create a calorie deficit – the good old fashioned way with healthy eating and exercise.

Join our Newsletter for the latest news right to your inbox