While that's not an unreasonable question, it often implies an approach that is less than optimal, which is to plan on adopting a radically restrictive mode of eating for a while, until the weight is lost, and then going back to eating as normal. Instead of embracing "fad diets," people who have lost weight—and kept it off—usually have made a permanent shift toward healthier eating habits. Simply replacing unhealthy foods with healthy ones—not for a few weeks, but forever—will help you achieve weight loss while also offering numerous other benefits. So a better set of questions might be, "What is a healthy diet? What does a healthy diet look like?"

A healthy diet favors natural, unprocessed foods over pre-packaged meals and snacks. It is balanced, meaning that it provides your body with all the nutrients and minerals it needs to function best. It emphasizes plant-based foods—especially fruits and vegetables—over animal foods. It contains plenty of protein. It is low in sugar and salt. It incorporates "healthy fats" including fish, olive oil and other plant-derived oils.