Psyched because you lost 20 pounds in a month, and all it took was—you know—denying yourself necessary, nutrient-packed foods? Maybe you spent the past four weeks eating only baby food, guzzling grapefruit juice, or eating a plain salad three times a day. Indeed, weight lost 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, like carbs, 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 UPMC 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.
You can check the nutritional completeness and safety of 29 popular diets ranked by U.S. News, from Atkins to Jenny Craig 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 the healthiness scores are ratings by a U.S. News panel of experts in nutrition and diet. They assessed the 29 popular diets in seven categories, including the safety and nutritional completeness categories, for a series of rankings released last June.
"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.
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, Dukan, and Atkins diets. They're simply too restrictive, say our experts, which calls 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.
If you have reservations about a diet's nutritional content or safety, listen to your body. Fatigue, sleeplessness, dizziness, aches—they're all red flags. Says Fernstrom: "Losing weight is for good health, so you should feel more vital—not bad."
Updated 01/08/2013: This is an updated version of a previously published story.