What Makes a Healthy Diet?

Not all diet plans are nutritious and safe. U.S. News rankings rate each diet’s healthiness.

Best Diets 2014 -- Pear with measuring tape around it
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A healthy diet doesn't require a lot of money or newfangled appliances or subsisting on any kind of scheme that sounds like a gimmick. Because it's true what they say about what seems too good to be true. Eating well means listening to that little voice inside that knows what healthy foods generally look like – fresh and recognizable in nature – and what they don't – prepackaged and processed.

That sensibility may not fit so well with our on-demand culture, where we want results now – be it dinner or weight loss. But if you want a program that works for the long run, you'll need a lifestyle you can live with and like. That means a diet that's nutritious and delicious, but one that will take a bit of planning and commitment from you.

[Read: The Inconvenient Truth of Healthy Living.]

While staying lean is a big part of good health, weight lost doesn't doesn't always equal health gained. That new diet that took inches off your waistline could be harming your health if it locks out or severely restricts entire food groups, relies on supplements with little scientific backing or clamps down on calories to an extreme.

"People are so desperate to lose weight that it's really weight loss at any cost," says Madelyn Fernstrom, founding director of the University of Pittsburgh Medical Center Weight Management Center and author of "The Real You Diet." And when that desperation sets in, says Fernstrom, "normal thinking goes out the window." Who cares if the forbidden-foods list is longer than "War and Peace"? Pounds are coming off. You're happy. But your body might not be.

With our 2014 rankings of Best Diets, you can check the nutritional completeness and safety of 32 popular diets, from Atkins to the Acid Alkaline diet to Weight Watchers, in a detailed profile crafted of each one. (The profiles also cover scientific evidence, typical meals, and much more.) And U.S. News's Best Diets for Healthy Eating rankings give each diet a "healthiness" score from 5 (best) to 1 (worst) for safety and nutrition, with safety getting double weight; while you can modify a diet to some degree to adjust for nutritional imbalances or deficiencies, mere tweaking won't make an unsafe diet safe.

Behind these scores are ratings by a U.S. News panel of experts in diet and nutrition. They assessed the diets across eight categories,including the safety and nutritional completeness categories, for a series of eight different rankings lists. The Best Diets for Healthy Eating rankings overlap significantly with Best Diets Overall. Both give especially high marks to the DASH, TLC, Mediterranean, Mayo Clinic, and Volumetrics diets.

"The ones that get high scores in safety and in nutritional value – they're very similar to each other," says Andrea Giancoli, a registered dietitian who serves on U.S. News's expert panel. The recurring theme across the diets that excelled in healthiness is adequate calories supplied by a heavy load of vegetables, fruits, and whole grains, a modest amount of lean protein, nonfat dairy, healthy fats and an occasional treat. Plants are the foundation, and the menu is always built around minimally processed meals made from scratch.

Because plant-based eating patterns are so healthful and are also growing in popularity, U.S. News now offers a Best Plant-Based Diets category. And given the rise of food intolerances and sensitivities, U.S. News has also included profiles of diets that are said to ease digestive distress – the gluten-free and the low FODMAP diets. These are not ranked, however, as they are not intended for general dietary needs.

[Read: Food Intolerance: Fact and Fiction.]

Very few diets in the Healthy Eating list are overtly unsafe or severely deficient nutritionally. The only plans to receive healthiness scores below 3 were the Paleo, Raw Food, Macrobiotic, Fast Diet, Dukan and Atkins diets. They're simply too restrictive, say our experts, who call their nutritional qualities into question. The meat-heavy Paleo diet bans grains and dairy, so getting adequate calcium and vitamin D isn't easy. Atkins, by severely curbing carbs, blows past recommended caps for total and saturated fat. Depending on your personal approach to the Raw Food Diet, you may shortchange yourself on calcium, vitamin B-12 and vitamin D; its restrictive cooking rules also could put you at risk for eating raw or undercooked ingredients.