If you cut your calorie intake and exercise regularly, you’re going to lose weight. That’s a no-brainer. But how effective are popular diets that say you can trim your waistline just by altering what you eat, such as taking in fewer carbohydrates, sticking with high-protein meals or eating like a caveman?

University of Florida researchers decided to find out. They searched the scientific literature for the most robust clinical trials for diets found on the 2016 U.S. News & World Report’s list of Best Weight-Loss Diets. Researchers excluded diets with specific calorie counts and structured exercise. That left them with 20 diets out of the 38 on U.S. News’ list.

The paper detailing their findings is bad news for many dieters.

Researchers reported to the journal Nutrients that they found little empirical evidence evaluating many popular diets. Researchers called that concerning because the diets are heavily marketed to the public. Of those 20 diets, just seven were evaluated by rigorous research.

As with many things in life, it’s always a good idea to do a little digging before accepting a claim that something will improve your life and health. Look under the hood.

The good news: Four of the seven diets evaluated demonstrated meaningful short- or long-term weight loss in clinical trials. Those diets were the Atkins, Mediterranean, Paleolithic and Zone diets.

Researchers warn, however, that these sorts of diets may not be right for everyone. And they also note this doesn’t mean it’s a bad idea to exercise or limit calories to lose weight, in consultation with your doctor.

So don’t get off your treadmill just yet.