The Three-Day Diet, also called the Cleveland Clinic Diet, Navy Diet and Army Diet -- although none of these organizations recommends it -- is a very restrictive, low-calorie regimen people sometimes try in an effort to lose weight very quickly. You're only allowed to eat a few foods on a more or less set menu, making it hard to get the nutrients you require, so check with your doctor before attempting to follow this diet.
There are a number of variations of this diet, but most recommend a breakfast consisting of half of a grapefruit, a slice of toast with peanut butter and black coffee or tea the first day. This is followed by tuna on toast with coffee for lunch and an apple, vegetables and 3 ounces of meat for dinner, along with vanilla ice cream for dessert. On the following two days, the meals have about the same number of calories, but they include hot dogs, small amounts of cheese or eggs as protein and varied fruits and vegetables at each meal.
This type of fad diet isn't recommended. Averaging 800 to 1,000 calories per day, it's too low to adequately meet your nutrient needs. Once you go back to your regular eating habits, you're likely to just regain any weight you've lost, which will most likely come from water weight and muscle instead of fat.
A better alternative would be to cut 500 to 1,000 calories from your typical diet each day by eating fewer sweets, fatty foods and refined grains. Instead, you would fill up on nutritious but lower-calorie foods such as vegetables, fruits and lean protein choices, including fish, beans and skinless chicken breasts. Exercise for at least 30 minutes most days of the week and you'll be on the way to losing a healthy 1 to 2 pounds per week.