Truth Squad: 4-Day Dieting and Other Weight Loss Trends

Now that the spring rains have given way to summer heat, many people are searching the Internet, browsing in bookstores, and asking their doctors about the best ways to lose pounds before hitting the beach.

Diet experts help ABCNews.com tackle the merits of fad diets.

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But the scope of popular diet advice is broad -- confusing and tantalizing at once with the promise of quicker, faster and better weight-loss results. If those promises don't deliver, discouraged dieters may give up their battle with weight for good.

Often, diet plans are structured to combat discouragement. The 4 Day Diet, a plan developed by Dr. Ian Smith, for example, advises a focused menu that changes every four days to prevent "food boredom."

"For successful dieting, you have to go through different pacing and different speeds," Smith said. "When you alternate the speed of the program, your body responds better to it rather than if you were dieting at the same pace."

But diet experts point out over and over that no one plan for diet and exercise will work for those who wish to lose weight unless it introduces significant changes in lifestyle habits.

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"Any diet that significantly reduces a person's calorie intake is likely to cause temporary weight loss," notes Joanne Ikeda, cooperative extension nutrition education specialist and lecturer in the Nutritional Sciences Department at University of California, Berkeley. "However, permanent weight loss remains an elusive goal for most people."

"There are some very silly -- and even dangerous -- ways to lose weight," said Dr. David Katz, co-founder and director of the Yale Prevention Research Center. "Where 'diet' books can offer innovation is in the 'how to get there' advice they offer; the 'what' is not up for grabs, since the fundamentals of healthful eating are well defined."

ABCNews.com rounded up some of the most popular diets to date and subjected them to the scrutiny of nutrition experts Ikeda, Katz, and Keith-Thomas Ayoob, director of the nutrition clinic at the Albert Einstein College of Medicine.

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The following pages feature each of these diets, as well as whether you can count on them to help you achieve a healthier weight.