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.
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.
"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.
The following pages feature each of these diets, as well as whether you can count on them to help you achieve a healthier weight.
1) The 4 Day Diet
What It Is: The 4 Day Diet is the brainchild of Dr. Ian Smith, and author and the diet consultant for VH1's Celebrity Fit Club, who found that people were not complying with their diet plans because they suffered from what he called "food boredom."
"People get tired of eating the same thing over and over again," Smith said. "This is a way to move the food around so people are eating good food and don't get tired of eating it because they know new foods are coming... Even if they were in a tough phase, they knew it would only last four days. From a psychological standpoint, that's a great boost."
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."
2) The Flat Belly Diet
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."
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."
3) The Full-Fat Diet
What It Is: The so-called full-fat diet builds off of research in January 2007 in which Swedish researchers found that women who had at least one serving of milk (whole milk, to be exact) or cheese each day experienced less weight gain over the following nine years than their counterparts who did not. Some concluded from this research that other full-fat daily foods may also provide these weight loss benefits -- though the researchers behind the Swedish study were hesitant to delve so deeply into the results to make a similar claim.
While the full-fat diet has many different versions, one of the most prominent proponents of eating foods in their full-fat form is New York-based nutritionist Esther Bloom, who delivers such advice in her book, "Eat, Drink and Be Gorgeous."
Ayoob: "I like the non-diet mentality of this. It's the idea that you can 'have your cake and eat it too.' But it's clear about this: you can't have it all the time and in all amounts. It's the idea that nothing is forbidden, and that's good."
Ikeda: "Although Esther Blum is an RD [registered dietitian], which gives her a plus for credibility in my book, her enthusiasm for supplements negates the plus with a minus. None of the endorsements on her Web site come from credible nutrition experts."
Katz: "I didn't find enough information about this to make a judgment, but the usual promises were made."
4) Low-Carb (Atkins) Diet
What It Is: The Atkins Diet was first popularized in 1972, with the release of the book "Dr. Atkins' New Diet Revolution." Controversial from the start, the diet is built around the idea that consuming too many carbohydrates is the main factor behind overweight and obesity. Therefore, by drastically reducing the intake of carbohydrates and shifting over to a diet high in protein in fat, a person can force his or her body to burn stored fat more efficiently.
The Atkins diet gained momentum at the beginning of the decade, and diet authors have published a host of new books aimed at further delving into the benefits of a low-carb approach to weight loss.
Ikeda: "Is this old thing still around? If it worked, obesity would no longer be a problem in this country, since a good percentage of the population has tried it."
Katz: "I think this is a silly diet at odds with health. It restricts choice very severely, which in turn restricts calories severely -- so it of course produces short term weight loss. But cutting out 'carbs' long term makes no sense; everything from lollipops to lentils is a 'carb,' so this diet throws out the baby with the bathwater."
Ayoob: "This is the original 'Full-Fat Diet.' Isn't America over this one yet? For people who plan to ditch their resolutions, this diet is for them -- people don't tend to stay with it very long. Just understand that when you finally let go of this diet, you'll have to go for something more realistic and not so limiting. Why not do that right from the start?"
5) The Mediterranean Diet
What It Is: In its purest form, the Mediterranean diet is designed to emulate the food choices of those who live in areas on the Mediterranean Sea, such as in Italy and Southern France. A true Mediterranean diet is predominantly plant-based, with plenty of fruits and vegetables, grains, beans, nuts, seeds and olive oil. It also incorporates some cheese, yogurt, fresh fish and poultry, with very little red meat.
Most nutrition experts caution that the Italian fare served at many Italian restaurants in the U.S. -- which is heavy in cheese, meat and fat -- should not be confused with a Mediterranean diet.
Ayoob: "This diet is famous for olive oil. Olive oil is great and it's heart-healthy, but it has as many calories as any other oil, even the less healthy ones. As such, the more olive oil you eat, the smaller your other portions are going to be. It's true that fat helps you feel satisfied, and this diet also focuses on lots of fruits and veggies, but it can be a little low in calcium, as dairy is not a huge part of the Mediterranean diet. I'd modify it to include low-fat milk."
Ikeda: "In looking at the [figures] below, one has to conclude that eating the way the French and Italians do might be quite beneficial."
Percentage of people classified as obese:
USA: Female = 34 percent; Male = 27.7 percent
Italy: Female = 9.9 percent; Male = 9.5 percent
France: Female = 7.0 percent; Male = 8.0 percent
6) Detox Diet
What It Is: While there is no single Detox diet, all are built around the idea that, by eating or avoiding certain foods, you can cleanse -- or "detoxify" -- your body. The toxins that are purportedly eliminated from the body through these diets are most often identified as chemical pollutants from the environment, along with supposedly harmful byproducts of human metabolism that linger in the body's tissues. Most Detox diets are intended to be temporary, lasting a few days or a couple of weeks.
Detox diets also provide a constant source of fodder for celebrity magazines, as stars including Gwyneth Paltrow, Angelina Jolie and Beyonce Knowles have reportedly tried them in the past.
Katz: "All Detox diets are rather silly. The body detoxes itself just fine. No real 'there' there."
Ikeda: "Doesn't anyone remember the lessons in human anatomy and how the body functions that were taught in elementary, middle school, and high school? Well, if one did remember, then one would realize that the body is self-cleansing -- like a self-cleansing oven. We get rid of 'toxins' daily in urine, feces, and sweat. If we didn't, we would be dead in a matter of days."
Ayoob: "This one is temporary; it's meant to be temporary, and that's not going to be of much help to most people. Even temporarily -- several days to a week -- it's a bad idea. It's mostly about fruits, steamed veggies, and not much protein at all. Bad idea. Stick to this diet strictly and you'll be losing muscle mass -- and that's your calorie engine... 'Detox' diets may have been around for years, but so has fasting, and I wouldn't recommend that as a means of weight loss either. Period."
7) The Zone Diet
What It Is: The Zone Diet, developed by Dr. Barry Sears, purports to balance the body's hormone levels within a specific range by controlling the foods that are consumed. According to the official website for the diet, "The Zone Diet can best be described as a moderate-carbohydrate, moderate-protein, moderate fat diet that has approximately one gram of fat for every two grams of protein and three grams of carbohydrates."
The Zone Diet places special emphasis on the moderate intake of low-fat protein, low glycemic-load carbs (such as those found in fruits and vegetables), and monounsaturated fats, as well as all needed nutrients.
Ayoob: "This one is fairly moderate, focusing on a good amount of lean protein, moderate fat and moderate carbs. Skip the vegetarian version if it's not your thing."
Katz: "I think this is too high in protein. It works by providing a strict dietary discipline, but suffers the same problem with sustainability as the others."
Ikeda: "Another oldie that had no impact whatsoever on the obesity epidemic in this country."
8) and 9) The Cleveland Clinic 3-Day Diet and The Mayo Clinic Diet
What It Is: Despite the names of these popular diets, both the Cleveland Clinic and the Mayo Clinic deny having any association whatsoever with them. This, however, does not seem to have impacted the popularity of either of these regimens, both of which are subjects of a high volume of Internet searches by those hoping to lose weight.
The Cleveland Clinic 3-Day Diet features a strict menu which is heavy on black coffee and light on calories. Proponents say those who follow the diet can lose up to 10 pounds in three days. The Mayo Clinic Diet on the other hand features a great deal of grapefruit juice and few, if any, carbs.
Ikeda: "If these diets worked, the Cleveland Clinic and Mayo Clinic would proudly take credit for them. They would publish books about them and make money off the sales. The problem is, these institutions are too ethical and know the diets don't work, so they distance themselves for good reason."
Katz: "These look ridiculous; they simply provide a detailed meal plan that restricts calories. As soon as you stop following these detailed directions, it's all over."
Ayoob: "First, skip any 3-day diet. If it's not meant for more than three days, you're likely just maximizing water loss, not much else. Go off the diet, the water weight returns and you've lost three days that could have been spent working on sensible eating... Any diet that only lasts a few days or a few weeks is a diet to be avoided. Better to get on some sneakers and do a fast walk away."
10) The Grapefruit Diet
What It Is: While these exists no one definitive grapefruit diet, all are based around a low-calorie approach, combined with a lot of grapefruit and grapefruit juice. The inclusion of this fruit is based on the idea that grapefruit contains a certain chemical or enzyme that aids weight loss.
Most of these approaches are short-term weight loss diets, lasting anywhere from a few days to a little more than a week.
Ikeda: "I wonder how many vitamin deficiency diseases one could achieve by staying on this diet long enough? Quite a few, but rest assured it wouldn't be scurvy since we all know that grapefruit gives us the big C [Vitamin C]."
Ayoob: "Back to the 'Mayo' diet, there are grapefruit versions of this, and the Mayo diet was also akin to the 'Cabbage Soup' craze in the 80s. Skip them. They're 10- to 14-day temporary fixes."
Katz: "Diets based on a single food work by restricting choice. But over time, restricting choice is incompatible with both health and dietary pleasure. Unsustainable."
11) The South Beach Diet
What It Is: The South Beach Diet, developed by cardiologist Dr. Arthur Agatston, is a three-phase plan intended to help adherents lose weight in the short term and keep it off long-term. Of the three phases, the first is the most restrictive, especially when it comes to carbs. Dieters are instead encouraged to include lean protein and high-fiber vegetables in their meals. Phases 2 and 3 gradually reintroduce non-refined carbohydrates and other dietary elements.
The diet plan also encourages exercise as a part of the diet -- a feature that proponents say distinguishes it as a healthy lifestyle rather than simply a diet.
Ayoob: "This one is pretty moderate. Developed by a cardiologist, it's heart-healthy. It tends to penalize refined carbs. They're really OK; just watch portions and go for whole grains whenever you have the choice. It also focuses on exercise, and that's the other part of the diet puzzle. Activity -- you've got to have it, or the diet works a heck of a lot more slowly."
Katz: "Surprisingly silly and short on substance, given the size of the following: cut out a lot of foods, add some back, then add some more back. At that point, if you start regaining weight, cut them all out again..."
Ikeda: "Where are the sequels? I'm waiting for the 'North Beach Diet,' the 'West Beach Diet,' and the 'East Beach Diet.' Or perhaps we need an 'Any Old Beach Diet.'"
Joseph Brownstein contributed to this report.
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