Eating healthy is an ever-evolving concept. The Paleo diet alone — or diets, based on some research — is a stark reminder that our primal ancestors ate very different than most of us today. But does that automatically qualify a diet made up mostly of meats and plants as the healthiest diet? Not quite.

In fact, an annual report of best diets from U.S. News & World Report ranked Paleo in last place. Per the report: “Regardless of the goal — weight loss, heart health or finding a diet that’s easy to follow — most experts concluded that it would be better for dieters to look elsewhere.” Even if you were to follow the diet to a tee, it’s difficult to procure very lean, pure cuts of meat and wild plants in modern society, thus being able to eat like real, healthier cavemen.

Diets that did earn high marks from U.S. News, however, were the DASH diet, the Therapeutic Lifestyles Changes (TLC) diet, the Mediterranean Diet, Weight Watchers, and the Ornish diet. The DASH diet, which was designed to help control blood pressure, was ranked the best overall diet for the fifth year in a row. Angela Haupt, senior health and wellness editor for U.S. News, said, "Our experts, who rate these diets for us say it will end up being very good for your waistline in addition to your high blood pressure because it is such a common-sense, balanced diet.”

The thing is, scientists don’t completely agree.

The Science Of A Healthy Diet

Researchers Dr. David Katz, founding director of the Prevention Research Center at Yale University, and Stephanie Meller conducted a study last year to see if it’s possible to categorize the best diet for health. Like U.S. News, Katz and Meller identified and compared popular diets, from low-carb to vegan diets, to see what they could find.

“There have been no rigorous, long-term studies comparing contenders for best diet laurels using methodology that precludes bias and confounding,” Katz and his team explained. “For many reasons, such studies are unlikely.”

It’s no surprise then researchers were unable to pinpoint a single best diet. Instead, they concluded it’s wise to stick with “minimally processed foods close to nature, predominantly plants." These are the basic fundamentals of so many of the diets we hear about today. Eating real, clean foods can equally benefit both health and weight loss goals. For some scientists, it doesn’t come down to a specific meal plan or set of rules — because when you eat and moderate real food, it doesn’t have to.

Another reason science struggles to pinpoint a best diet for health is because so many cater to different aspects of our health. U.S. News found the DASH and TLC diet were best for healthy eating, while Weight Watchers and the HMR (Health Management Resources) diet were the best for weight loss. The DASH diet, however, also tied with the Biggest Loser diet to best control diabetes, and the TLC diet came in second to the Ornish diet when it came to heart health.

The Ornish diet may be a top diet you're unfamiliar with. OK, it's a top diet we're unfamiliar with. Developed by Dean Ornish, a professor of medicine at the University of California, San Francisco, U.S. News reported this diet is "scientifically proven to make you feel better, live longer, lose weight, and gain health.'" It also severely cuts back on the daily recommended amount of fat intake. This isn't only problematic with regard to overall nutrition, but it lumps the good and bad fat together. Not all fat is created equal. Think of heart-healthy omega-3 fatty acids.

The Bottom Line

Harley Pasternak, author of The 5 Factor World Diet, told the Huffington Post all of the top diets tend to have one thing in common: physical activity.

"The only overlapping feature in most of these healthy countries around the world is that they all walk way more than the average American,” Pasternak said. "So really, regardless of what you’re eating, if someone’s walking 4 miles more than you each day, they’re going to be a lot thinner and live a lot longer than you."

Exercise combined with a healthy diet is going to untap the best, healthiest version of yourself every time. There will always be a list of the alleged best and healthiest diets; some will even be nutritionally and scientifically sound. But not all of them will be best for you.