"If you lined up all the diets in the world in a multimillion-dollar clinical trial and fired the starting gun, and lots of people started each of these diets, my prediction is early on there might be some separation, with some of these diets showing bigger weight loss than others," says Kelly Brownell, director of the Yale Center for Eating and Weight Disorders in New Haven, Conn. "But in the long term, they'd probably work the same overall."
Thus obesity researchers say that part of the key to successful weight loss lies with individuals picking diets they are most likely to stick with.
It also lies with lowering expectations and not trying to diet down to unrealistic, belly-baring Britney thinness.
Even more important is figuring out how to sustain weight loss long term, since most people who lose weight eventually gain it back. Perhaps, says Hill, they can tap the secrets of those who have succeeded in maintaining their new weights.
Most experts are convinced that stopping the long, mad procession of diet books will require a slew of changes: health insurance coverage for weight loss programs, more scientific studies of different diets, altered attitudes toward norms of weight and attempts to clean up an environment that is awash in high-calorie snacks and drinks and encouragements to sample them often and plentifully.
Brownell, for one, would like to see diet gurus required to put their data where their mouth is before they can make florid claims in bestselling books.
Dr. David Heber, director of the Center for Human Nutrition at UCLA, believes today's nutrition labels -- with many servings crammed into a single bag of chips and an unrealistically liberal percent of daily nutritional values -- are encouraging people to overeat. "People are confused when they read food labels: There's this mythical 2,000-calories-a-day person," he says.
Some doubt the tide of diet books can ever be stemmed. Optimistic researchers may predict a world in which the carousel of glitzy promises is replaced with sound, sober, rational advice that those who wish to lose or maintain their weight will obediently follow.
But others see shelves crammed with the white-toothed smiles of new diet gurus, and glossy reincarnations of tired old classics.
"Diets promise a quick fix," says the University of Toronto's Polivy. "People would rather have a quick fix. Wouldn't you want something fast and easy rather than long and arduous?"
Tomorrow, she says, "we'll see variants of the diets we see today -- with a new name and new sponsor."
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William the Conqueror tries a liquid diet for weight loss, taking to his bed and consuming nothing but alcohol.
1600s to early 1700
Scotsman Dr. George Cheyne, author of popular books "An Essay of Health and Long Life" and "The English Malady," uses liquids of a different stripe, writing that a milk diet renders him "lank, fleet and nimble."
The Romantic poet Lord Byron drenches his food in vinegar to lose weight, dropping his heft from 194 pounds to less than 130.
America's the Rev. Sylvester Graham, nicknamed "Dr. Sawdust," rails against the sin of gluttony, which he says leads to lust, indigestion and the rearing of unhealthy children. Graham's answer: a spartan diet of coarse, yeast-free brown bread (including the famous Graham cracker), vegetables and water.
* Rise of the low-carbohydrate diet. London undertaker William Banting loses 50 pounds on a high-protein regimen that consists of lean meat, dry toast, soft-boiled eggs and vegetables. His 1864 book "Letter on Corpulence" becomes a bestseller; by 1880s "banting" is America's foremost weight-loss strategy.
* Another high-protein proponent, Dr. James Salisbury, promotes a diet of hot water and minced meat patties (the famous Salisbury steak) for improved health and weight loss.
Dr. John Harvey Kellogg becomes staff physician of the Battle Creek Sanatorium in Michigan. A leading diet guru, he crusades over the years for vegetarianism, pure foods, slow chewing, calorie counting, colon cleansing and individualized diets. He invents granola and toasted flakes.
Milk diets, earlier prescribed for indigestion and weight gain, become popular for weight loss.
Dr. Edward Hooker Dewey promotes a moderate fast, the "no-breakfast plan," as a weight-loss strategy. Other doctors widely recommend limiting alcohol and substituting carbohydrates with proteins.
The slow-chewing movement is founded by businessman Horace Fletcher. After he is denied life insurance because of his weight, Fletcher drops 40 pounds through a strategy of chewing each mouthful of food to liquid before swallowing it. "Fletcherism" takes off, rah-rahed by diet guru Kellogg, who invents a slow-chewing song for his patients.
Food scales, developed for diabetics, and calories become central to diet plans. "Without scales, no cure," writes Viennese doctor and food scale inventor Gustave Gaertner, author of "Reducing Weight Comfortably."