Enough calories to keep you healthy. If a diet provides fewer than 1,200 calories per day, experts say you should be under a doctor's supervision.
A good range of food choices. Some diets eliminate certain food groups. Vegetarian diets, for example, do not allow meat and low carb diets do not allow grains, even whole grains. However, in general, despite these restrictions, a diet should offer a wide range of food choices. Diets based upon one main ingredient -- fruit, say, or nothing but broth -- are not considered healthy.
Real food. Delivered meals and proprietary meal-replacement diets are convenient and can be effective weight-loss tools, but ultimately you need to learn to cook healthful meals for yourself. Any diet you choose should give you the knowledge and tools to do so.
Gradual, sustainable weight loss. Fad diets that promise sudden weight loss may be appealing, but the pounds usually come right back on, and fad diets can be harmful to your health. Losing weight slowly but steadily makes it more likely you will succeed over the long term.
Support when you need it. Not everybody wants group meetings or an online diet buddy, but having some form of professional guidance and peer support available when you need it -- whether online, by telephone or in person -- is a valuable resource.
Flexible eating plans. The best diets are flexible enough to accommodate almost any dietary need or preference, including vegetarian, vegan, gluten-free, low-sodium, kosher and halal.
Long-term maintenance goals. Learning maintenance skills -- basically, a new lifestyle -- helps you keep the weight off once the diet's over.
A clear pricing structure. Most diet programs are honest and upfront about their costs, but quite a few draw complaints for hidden fees, pricing structures that aren't revealed until you commit to the program, and less-than-transparent billing practices.
No diet pills. If the plan you're considering requires you to buy pills, its focus is on you losing money, not weight. Over-the-counter weight-loss supplements, which don't require approval from the FDA, can even interact with other drugs you may be taking and pose a health hazard. Diet pills may be used in conjunction with a physician-prescribed weight-loss program, but only under your doctor's supervision. For more discussion of supplements aimed at weight loss, see our separate report on diet pills.
What does your doctor say? Everyone should check with their personal physician before going on a diet, but it's crucial if you have any health issues at all. Your medical team can help you determine your ideal goal weight, and, if your plan involves calorie counting, they can help you set a safe caloric goal for yourself. They can also help you identify and manage any underlying health conditions, including diabetes, and any food intolerance issues.
What type of support are you comfortable with? Studies show that dieters who have a support system are more successful than those who try to go it alone. Some folks prefer group support, while others would rather have individual attention. Many do fine with an online buddy or community. If you choose something that fits your lifestyle and preferences, you're more likely to stick with it.
Do you like to cook? Virtually all diets have meal plans and recipes to accompany them, but some are more complex than others. If you're practically a gourmet cook, just about any diet will suit you; if you hate to cook or just aren't good at it, look for simple meal prep options or even a prepackaged plan.
What are your long-term goals? The best diets help you incorporate all elements of a healthy lifestyle, such as fitness, life-long eating strategies, stress management, recognizing psychological or situational triggers for overeating, or developing an appropriate body image.
All diets work. The trick is to find one that you can stick with for the long term, with a minimum of cheating, boredom, or bewilderment. The best way to do that is to look at some issues people commonly face when dieting, and tailor your diet to those that may affect you. Based upon our research for this report, we offer these general guidelines in choosing a long-term diet plan. As with any lifestyle change, be sure to consult your doctor before making any changes to your diet to be sure there are no contraindications or underlying health issues.
You like structure. Weight Watchers is a great choice for people who like a lot of guidance. Tracking is very simple and the program is laid out in a way that makes it virtually foolproof. Meal plans are complete and easy-to-follow, and they offer a lot of recipes and menu suggestions. They even help you specifically track how much of various nutrients you are eating.
You're hungry all the time. The DASH Diet, Volumetrics, Paleo and low carb offer alternatives to calorie counting. Rather, you eat until you are satisfied from specific types of foods that offer bulk and fewer calories.
You are gluten or dairy intolerant. Most diets can be tweaked to exclude gluten, but several -- most notably low carb and Paleo -- do not allow any gluten-containing items in their guidelines, which may help you avoid accidentally ingesting something that doesn't agree with you.
You don't want to exclude certain food groups. Avoid low carb and Paleo as they ban popular foods like pasta, bread and most (or all) dairy. Instead, focus on programs like Weight Watchers, DASH and Volumetrics, which assign values to food to keep the calorie count down, but don't forbid anything.
You have type 2 diabetes. The DASH diet is considered a top diet for controlling diabetes. Be careful with plans that offer unlimited fruits or starches, such as Weight Watchers and Paleo. Diabetics need to count these as part of their total carb intake.
You have hypertension. The DASH Diet was specifically designed to help control high blood pressure via dietary changes that include reducing salt intake. However, experts say that any positive change to your diet that results in weight loss will most likely lower both blood pressure and cholesterol.
You are an emotional eater. If your stomach is ruled by your emotions, you'll want to look for a plan, like Weight Watchers or Jenny Craig, with a strong support component. Counselors are on hand virtually 24/7 to talk you off the binging ledge.
You can't, or don't want, to cook. Most of the diets in this report are based upon shopping for and cooking whole foods. Jenny Craig and similar prepackaged diet plans deliver prepared food right to your door; however, they can be pricey. Weight Watchers is probably the easiest of the non-prepackaged diets to follow if you're not a cook because they have so many food options, with many that are extremely simple to make as well as a wide range of frozen entrees. Paleo is probably the most food-prep intensive, since its entire focus is on cooking your own food and can be overwhelming even for those who enjoy cooking.
You don't have a lot of financial resources. There are many free diet plans, such as the DASH and TLC diets, as well as very inexpensive books, like Volumetrics. Many well-established diets, like Atkins, have guidelines that are freely available around the Internet. In addition, used books can be purchased for pennies, and can be checked out for free from your local library. Don't worry about getting the latest edition either, most updated versions of diet books are merely a refresh -- the original plan will still work. Also, check out free sites, like MyFitnessPal.com and SparkPeople.com. They offer diet plans, exercises, and support at absolutely no charge.