Find your best diet for 2008

If you're considering a nutritional makeover in 2008, you're not alone.

"As New Year's Eve marks the end of the holiday party season, shoppers take their resolutions straight to the stores," says Todd Hale, a vice-president of market research firm Nielson Co.

That presents a golden opportunity for pedlars of diet products. Sales in January will be double what they were in December, according to forecasts released by Nielson last week --so manufacturers of these diet aids should "brace themselves for a banner month," Hale advises.

But if you're looking for a more sustainable -- and successful -- approach to a healthy diet, the job of formulating resolutions is quite a bit more complicated.

It sometimes seems like the advice on how to eat well changes weekly. Since September, the results of nearly 300 new nutrition studies have been distributed through the press-release service of the American Association for the Advancement of Science. And they don't always agree with each other.

Take the case of sugary drinks. In September, a Tufts University study found that drinks sweetened with sugar (soft drinks, primarily) were associated with increased insulin resistance, a precursor to diabetes, but pure fruit juices, which are naturally sweet, were not.

A week later, a British study in the International Journal of Food Sciences and Nutrition found that increased soft drink consumption had no link to increased weight in children, suggesting that previous studies of the "alleged links" were "flawed." This study was funded by The Sugar Bureau.

Then in November, a study from the University of Carolina at Chapel Hill suggested that calories from drinks -- this time including pure fruit juices as well as soft drinks -- contribute to adult obesity and possibly diabetes.

Another hot topic is the role of folate, a B vitamin found in green vegetables. Since 1999, folate levels have been boosted by the addition of folic acid to flour in Canada, to help prevent certain birth defects. A recent study at the University of York in Britain found that folate could also fight depression, and a Northwestern University study suggested that it lowers stroke risk.

But another series of studies has suggested that high levels of folate due to the flour additive program have led to a surge in colon cancer in Canada. And a Tufts study released last week found that high folate levels could interfere with the action of vitamin B12, raising the risk of anemia and cognitive impairment in older adults.

"Folic acid supplementation wields a double-edged sword," says Dr.

Young-In Kim, a professor of medicine and nutritional sciences at the University of Toronto. "It may be beneficial or harmful, depending on the timing of intervention." This may seem like unpardonable flip-flopping, but it's an inevitable part of the scientific process, as researchers test -- and sometimes reject -- hypotheses about how the body actually works. The same is true in every science; the difference is that astrophysicists' constantly changing estimates of exactly how old the universe is don't usually affect our daily lives.

We've also been told that the latest antioxidant superfood is strawberries. Not just any strawberries, mind you, but wild strawberries, which the American Society for Horticultural Science suggests that farmers should begin to grow and market.

But history suggests that not all of these "breakthroughs" will still be considered good advice a decade from now.

As a cautionary tale, consider these resolutions that health-food devotees might have made in years past before embarking on yours for the new year:- 1952 -- Blackstrap molasses Gayelord Hauser, nutrition guru to stars like Greta Garbo and Louis Armstrong, published Look Younger, Live Longer in 1951, recommending yogurt, powdered skim milk, brewer's yeast, wheat germ and especially blackstrap molasses for their healthful effects. The book sparked a surge in the popularity of blackstrap molasses, according to Catherine Carstairs, a University of Guelph professor who is studying the history of health foods in Canada. The craze was so powerful the U.S. Food and Drug Administration twice seized shipments of Hauser's book, along with bottles of molasses, claiming that the promised health benefits were exaggerated.

- 1965 -- Brewer's yeast This foul-tasting substance, touted by Hauser, was in vogue from the 1950s up to the 1970s as a source of B vitamins. Another advocate was Adelle Davis, whose bestselling health-food books were first published in the 1950s, but reached new heights of popularity in the 1960s, Carstairs says. Davis suggested downing brewer's yeast in her "pep-up" drinks, which also featured eggs, lecithin, vegetable oil, yogurt, kelp, powdered milk, orange juice, wheat germ, magnesium and calcium.

- 1971 -- Megadoses of vitamin C Two-time Nobel Prize-winning chemist Linus Pauling published his bestselling book Vitamin C and the Common Cold in 1970, sparking such an enthusiastic rush that drugstores couldn't keep enough pills in stock. Pauling himself took 300 times the recommended daily intake of vitamin C until his death in 1994, but not before publishing followup books claiming that it also helped fight the flu and cancer. The most recent research review, published earlier this year, concluded that taking 200 milligrams or more of vitamin C daily had little effect on the length or severity of colds -- although people under high physical stress, like marathon runners, were less likely to catch a cold when taking at least 200 mg of vitamin C daily.