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Dieting is a struggle for many people. Numerous popular diets offer the promise of weight loss. But which ones work? University of Florida Health researchers decided to find out.

While they found little scientific evidence showing whether many diets were effective, some diets demonstrated meaningful short- and long-term weight loss 鈥� a weight loss of 5 percent 鈥� in clinical trials.

Researchers, however, looked only at diets without calorie counts and/or recommendations of vigorous exercise, which are guaranteed to lead to weight loss. Do popular diets based only on what we eat 鈥� low-carbohydrate, grain-free diets and others 鈥� lead to a trimmer waist?

鈥淣ot all diets showed clinically meaningful weight-loss outcomes, said the study鈥檚 lead author, , division chief of clinical research for and a member of

Researchers searched for clinical trials evaluating the effectiveness of 38 popular diets listed on U.S. News & World Report鈥檚 2016 ranking of 鈥淏est Weight-Loss Diets.鈥� After cutting diets listing specific calorie targets and/or exercise recommendations, they were left with 20 popular diets.

Of these, seven had been evaluated in clinical trials that met strict criteria set by researchers. And just two of those diets were evaluated by three or more trials.

鈥淭he small number of clinical trials examining the efficacy of many popular diets is concerning, as it indicates relatively little empirical evidence exists to support many current popular diets available, which are heavily marketed to the public,鈥� said the study, recently published in the journal Nutrients.

According to U.S. News 鈥淏est Diet鈥� methodology, a panel of experts examined research regarding each diet鈥檚 potential to produce both short- and long-term weight loss and assigned ratings. But UF researchers included only interventional clinical trials with at least 15 participants per group, study periods of at least 12 weeks, inclusion of study participants with a body mass index of at least 25 kilograms, and objective measures of weight with no self-reporting. They also excluded studies that did not follow the diet as prescribed.

The low-carbohydrate Atkins Diet came out far ahead of the pack, with 10 clinical trials evaluating either short- or long-term weight loss. It was followed by the moderate-carbohydrate Zone Diet, with three clinical trials. Those with two clinical trials apiece were the Glycemic-Index Diet, which emphasizes 鈥済ood carbs鈥� like bran cereal and vegetables; the Mediterranean Diet, rich in fruits, vegetables and whole grains; the Ornish Diet, a low-fat, vegetable-based program; and the Paleolithic Diet, based on foods available to early humans 2.5 million to 10,000 years ago. Finally, the Dietary Approaches to Stop Hypertension, or DASH, Diet 鈥� low in saturated fats and sodium 鈥� with one trial.

Nine of the 10 clinical trials evaluating the Atkins Diet demonstrated clinically meaningful short-term weight loss, and six of eight long-term Atkins clinical trials demonstrated long-term weight loss. (Some individual studies examined both long- and short-term weight loss.)

Other diets that demonstrated clinically meaningful weight loss in at least one study were the Mediterranean, Paleolithic and Zone diets.

Researchers said their review suggests that high-fat, low-carbohydrate diets 鈥渁re the most advantageous鈥� for promoting long-term weight loss.

鈥淔or not having specific calorie limits and not being paired with a formal exercise program, the magnitude of the weight loss on some diets was surprising and quite extensive,鈥� said Anton. 鈥淣ot to say this would work for every person, but it does suggest a potential approach that is successful for many people.鈥�

The study鈥檚 co-authors include , a professor and vice chair of research for UF鈥檚 department of aging and geriatric research and a member of UF鈥檚 Institute on Aging; , an associate professor and member of the Institute on Aging; Azumi Hida, Ph.D., formerly a visiting scholar at the Institute on Aging from Tokyo University; and UF research assistants Kristen Sowalsky, Ph.D., Heather Mutchie and Christy Karabetian, Ph.D.