Volumetrics is the best carefully researched diet plan, and "The Best Life Diet" is the best diet book, Consumer Reports says.

Volumetrics is based on the research of Penn State nutritional science professor Barbara Rolls, PhD. The Volumetrics diet stresses eating foods with low "energy density" — that is, foods with relatively few calories per portion. Such foods include fruits, salads, and soups.

The Best Life Diet, by personal trainer and exercise physiologist Bob Greene, stresses exercise and gives personalized advice, including recipes and a recommended eating schedule.

To rate the diet plans, "Consumer Reports" Senior Project Editor Nancy Metcalf and colleagues reviewed diet studies published in major medical journals. After Volumetrics, Metcalf's team ranked Weight Watchers, Jenny Craig, and Slim-Fast "very close together."

The report gave middling ratings to eDiets and to Barry Sear's The Zone Diet. Bringing up the rear were Dean Ornish's Ornish Diet and, in last place, the Atkin's Diet.

To rate the diet books — newer diets that, according to "Consumer Reports," "have not been put to the acid test of a large clinical trial" — the CR staff applied their own criteria and also got input from a panel of nutritional experts.

After "The Best Life Diet," CR ranked three books as "very close to one another:" "Eat, Drink, & Weigh Less" by Mollie Katzen and Walter Willett, MD; "You On a Diet," by Michael F. Roizen, MD, and Mehmet C. Oz, MD; and "The Abs Diet" by David Zinczenko with Ted Spiker.

Ranked last among the diet books — behind "The South Beach Diet" by Arthur Agatston, MD; and "The Sonoma Diet" by Connie Guttersen, PhD, RD — was "Ultra-Metabolism" by Mark Hyman, MD.

The ratings appear in the June issue of "Consumer Reports."

Diet Authors Respond

"We set up criteria that make sense to us, and let the chips fall where they may — hopefully not chocolate chips," Metcalf tells WebMD. "The things that go into the rating are the nutritional analysis — we analyze a week's worth of menus straight off the book or Web site — and we also rate them according to how well they conform to the 2005 U.S. dietary guidelines, which we think is a good consensus on a healthy diet."

For the diet plans, that may not have been the best strategy, says low-carb-diet expert Eris Westman, MD, associate professor of medicine at Duke University Medical Center. Westman was a member of the "Consumer Reports" expert panel that helped rank the diet books.

"When you compare a weight loss diet to a healthy-eating guideline, of course it is going to look bad because it is restricted in calories and, perhaps, in carbohydrates," Westman says. "This is a common point of confusion. If you have diabetes, can you follow the healthy-diet guidelines? No! You are not healthy: You have diabetes and need a different kind of diet."

Westman says that even though the Atkins Diet got the lowest ranking among diet plans, the highly tested plan is more likely to work than the untested diet books that got more of "Consumer Reports" coveted red bubbles (high scores) and fewer of the dreaded black bubbles (low scores).

The recipient of many blank bubbles (average scores), Dean Ornish, MD, says "Consumer Reports" misrepresents his diet and overlooks "30 years of studies published in peer-reviewed journals that support our claims."

"It's not only important to lose weight but to do so in a way that is most healthful," Ornish says. "The diet I recommend is based primarily on fruits, vegetables, whole grains, legumes, soy products, and a little fish, and is low in refined carbohydrates and high in whole grains. Most authorities consider this the most healthful way to eat."

Moreover, Ornish says he is mystified as to why the Volumetrics diet gets a high score while his gets a low score, as both stress low-energy-density foods.

Differences in Fat Restriction

Volumetrics creator Rolls says she and Ornish differ mainly in fat restriction. Ornish's diet stresses reducing fat intake to 10 percent of calories.

"You can have fat in your diet if you also have a lot of veggies and fruits to offset the fat," Rolls says. "We show that people who eat a high-fat diet — more than 30 percent of calories from fat — but who eat a high number of servings of fruits and vegetables, actually had a lower incidence of obesity than those eating a low-fat diet with few fruits and vegetables."

Understandably miffed by the "Consumer Reports" rankings is "Ultra-Metabolism" author Mark Hyman, MD. The article says Hyman's theories of nutrition "goes beyond scientific evidence."

"The science I use may be ahead of its time, but it is still science," Hyman says. "My book is the only one to deal with the underlying causes of disease, which also underlie obesity. The same things that make you sick make you fat — and the things that make you fat make you sick. This is not being paid attention to by conventional medicine."

Hyman says the consumer group's low ranking of his book is due to a "dangerous" over-reliance on the USDA diet guidelines, which he calls "watered down to meet the special interests of industry."

"Eat real foods, whole foods. That is the essential message of my book," Hyman says. "That means eating foods that come from the land and not from a food chemist's laboratory."

Exercise: 'A Tough Sell'

First-ranked diet-book author Bob Greene is less vexed by "Consumer Reports'" mild criticism of his work. The article says that dieters "might be discouraged when they don't lose weight in phase one" of the diet.

"People might very well be discouraged at first. That is why I spend most of my time motivating people and getting them away from their addiction to scales," Greene says. "Exercise is a tough sell. But we humans were meant to move, from a weight loss standpoint as well as from a health standpoint. "

Exercise alone isn't enough, Greene says, unless you are getting at least a full hour of strenuous exercise every day.

"Most of the population won't devote that amount of time to exercise, so they have to watch their food intake," he says. "But if you are consistent with moderate exercise, you place a ceiling on your weight gain. Then you earn your result: the level at which you set your calories."

CR's Metcalf warns that no diet can work miracles. Some people lose 30 pounds or more on any of the diets. But most people will get much more modest results.

"None of these diets, even the highest rated, created a lot of weight loss — 10 pounds at best," she says But people shouldn't be disappointed. Small weight losses can have big health effects."