A San Diego physician is quickly joining the ranks of Internet phenomenons with one of the world’s first viral diets. Fans of his 17-Day Diet have taken to Twitter, YouTube, and the blogosphere to sing the praises of Dr. Mike Moreno’s weight-loss regimen. Already a best seller, his new book professes the power of the number 17. With 17 minutes of daily exercise and four different 17-day meal plan cycles, the diet promises dramatic weight loss results for life. Broken into four different parts, the plan is designed to jump-start the body’s metabolism by switching up eating habits every 17 days. The first cycle involves a restrictive calorie diet, and the other three toggle between various carbs, proteins, fruits and veggies for an overall healthy makeover.

"I think this diet is probably the only diet that is for everybody," Moreno tells ABC News. "And that means whether you want to lose five pounds for your high school reunion coming up, whether you want to lose 150 pounds, or whether you're just comfortable with who you are and how you look and your health and your weight, as it is, this is just a way to not only focus on the scale moving, but it's focusing on good, proper digestive health." Flexibility is one big thing that’s setting Moreno’s bestselling diet book apart from the others. Based on the sheer numbers of proponents, the diet accommodates a lot of different lifestyles. But not everyone is on board—some nutrition experts have their reservations about Moreno's meal plan. Here, they weigh some of the pros and cons.

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Pros:

It doesn’t get monotonous. The plan itself is 68 days long, but it’s broken up in four parts, 17 days a piece. “Since it divides weight loss into little chunks, each cycle seems doable,” says nutritionist Laurie Slayton, who runs the diet website foodtrainers.net.

The results are fast. “You get good results in the first phase especially,” adds Slayton. During the first 17 days, dieters can lose up to 15 pounds by eating a restrictive diet of 1,200 calories a day. Seeing results so fast makes for some serious motivation to stick with it.

There’s a long-term emphasis. The first 17 days are the most extreme, but the second cycle introduces more calories and the chance to shed another 5 pounds and the last two cycles are designed to integrate healthier overall eating habits into your long-term lifestyle. Swapping out mayo for mustard, and sugars for nectar and spices are some of the basic principles for keeping off the weight. “If you eat a highly processed diet this could be a good switch,” says Slayton. “If you are a healthy eater you already know things like egg whites, fish, and vegetables are good for you.”

It’s fairly balanced. Unlike the Atkins diet, Moreno’s plan doesn’t completely cut out one major source of nutrition. Fruits, veggies, protein-rich meats and healthy carbs are all part of the constantly shifting meal plan so your body is never completely deprived of one thing. Overall, it's considered fairly safe as opposed to more high-risk deprivation diets and cleanses.

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Cons:

The scientific proof isn’t totally convincing. Moreno claims that shifting your meal plan every 17 days before your body registers certain eating habits is a way to keep your metabolism in high gear, but not everyone is buying it. "There is no scientific evidence to support the efficacy of calorie cycling or its effect on metabolism,” Mary Hartley, director of nutrition at Calorie Count, tells the editors of Diets In Review. "There is no harm in calorie cycling temporarily or indefinitely and the process happens naturally for most people, who don't eat or burn the same number of calories every day."

Marisa Sherry, a registered dietician, questions one hard-and-fast rule of the diet—no starchy carbs or fruit after 2 P.M. "There's no proof that after certain times of day your body loses the ability to digest carbohydrates," Sherry tells CBS News.

The first 17 days of calorie restrictions may backfire: "You are cleansing your body of the unhealthy foods you have been eating," says Sherry. "But if you are not consuming enough calories to meet your resting metabolic needs, then you are in starvation mode which actually slows your metabolism."

It’s an investment: While there’s plenty of store-bought foods that fall into the meal plans, dieters are encouraged to buy specific 17-Day Diet branded snacks like the breakfast cookie. That can rack up your bills unnecessarily.

It's complicated: “I have two nutrition degrees and found the explanations a little confusing,” says Slayton. Since the guidelines of the diet are constantly shifting, following the plan takes focus, organization and the constant recording of calorie intake. Still, the basic principles are simple. "Cut your calories and increase your exercise, that's how it's done," Sherry tells CBS News. "If you can get away from the rules that aren't based on science, it should work just fine."

Would you try this 17-day diet?

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