The Truth About 10 Trendy New Year's Diets

1) The Flat Belly Diet

What It Is: The Flat Belly Diet, which was launched by "Prevention" magazine editor-in-chief Liz Vaccariello, is a plan that 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.

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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 4-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.

Expert Verdict:

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."

Ikeda: "This diet is based on the premise that a higher intake of monounsaturated fatty acids will result in a flat abdomen. There is nothing in the scientific literature that substantiates this claim. The best way to get a flat belly is to increase the strength of abdominal muscles by exercising them."