Smith's plan is based on seven mix-and-match four-day-long modules that consist of a defined food group or plan. For example, the Induction module is meant to detoxify and cleanse the system while the Protein Stretch module incorporates foods like eggs, lean meat and vegetables and the Smooth module allows people to indulge in forbidden favorites such as pizza. Together with exercise, Smith said his modules keep the body from becoming accustomed to one diet plan.
Expert Verdict: Katz: "Obviously there is no science to back this up. The ultimate goal of 'dieting' should be to establish a stable, healthful dietary pattern; I see no hope whatsoever of that here. So this is all about, and only about, short term weight loss -- which just about any diet can provide... What is the right answer? Learn to choose wholesome foods; learn to use them in wholesome meals; and make a lifelong commitment to healthful eating and regular activity that includes the other members of your household. That's the truth."
Ayoob: "This diet has some nice aspects to it, but balance isn't one of them... It's different each day, it's not boring. It encourages you to keep a food diary. It allows you an occasional indulgence so you don't feel deprived. Lots of fiber, fruits, and veggies. I especially like that it includes beans -- a terrific food. [But] some dieters will find that they need at least some consistency. Lots of different calorie intakes over the four days; some are really low, some not."
Ikeda: "Like most diets, [this one] can result in weight loss... My big criticism of this diet is it does not teach people how to eat a healthy, well balanced, nutrient-dense diet that they can keep eating for the rest of their life... And I don't care how well one eats, if a person is not physically active, they are not going to be healthy."
What It Is: The Flat Belly Diet, launched by "Prevention" magazine editor-in-chief Liz Vaccariello, is built around a 1,600-calorie-per-day strategy that allows dieters to eat four meals per day selected from hundreds of meal possibilities.
Central to the diet is the principle that every meal must contain a source of MUFA -- short for monounsaturated fatty acids. According to the diet's proponents, these predominantly nut-based oils can target-reduce dangerous belly fat. The diet also commences with a four-day jumpstart to get rid of abdominal bloating, during which a dieter drinks what the proponents of the diet call Sassy Water, a lemon- and ginger-containing beverage named after "Prevention" nutrition director Cynthia Sass.
And according to a small MRI imagine study released Monday out of the Yale University Prevention Research Center, the diet reduced visceral belly fat on average by 33 percent in 28 days for nine overweight women. Other risk factors, such as high cholesterol and blood pressure, were also reduced in the study participants.
Katz: "[The diet is] generally healthful, with an emphasis on foods noted as being good for insulin resistance. My lab actually studied the effects of this short term, and they were quite good."
Ayoob: "You may have a flatter belly in 32 days but that's because you're losing weight, pure and simple. Make no mistake, your body will determine where you lose weight. It tends to come from the belly first anyway -- that's usually the body's first preference -- but it's the weight loss that's flattening your belly, not some diet miracle."