Every day, millions of Americans are on diets or are vowing to begin one.

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A new Consumer Reports survey rates the various diet plans but stresses that experts say the best diet is the one you can stay on.

The consumer magazine calculated the diets' calorie counts and nutritional composition, checked whether they conformed to U.S. dietary guidelines, and evaluated their effectiveness with a review of clinical research.

Among the magazine's findings:

Weight Watchers received the highest overall rating. The magazine said it provided the best combination of nutrition and producing a slow but steady weight loss. It also had the highest long-term adherence rate of any diet studied. This plan doesn't exclude any food group, and its point system encourages consumption of low-fat, high-fiber meals.
Slim Fast, which received the second highest rating, is recommended for people who don't like to cook: Branded bars and drinks replace part of breakfast and lunch, and dieters need to prepare only one full meal a day. People on the Slim Fast plan lost the most weight in six months using products like 180-calorie shakes.
The Zone is high in protein and includes copious amounts of high-fiber vegetables. Many companies offer home delivery of "Zone-favorable meals." It is recommended for those who want a short-term high-protein diet plan.
Ornish offers ultra low-fat, high-fiber vegetarian meals, which provide fairly large portions for the low calories.
Atkins Induction and Atkins Ongoing Weight Loss are appropriate for people who want a short-term high protein diet plan. The Atkins diet worked very well in the short term, with results at least as good as our other top-rated diets. But its nutritional deficiencies -- too much fat, and too little fiber and too few fruits -- lowered its overall rating and may have a negative effect on some people's health.

Some diets -- including eDiets, Jenny Craig, South Beach, and Volumetrics -- weren't rated because they didn't publish menus or there isn't any data from long-term clinical trials.

But the study, published in the June issue of the magazine, stressed that a diet that works for one person may not work for another.

Senior editor Nancy Metcalf said the only way to find out if a diet is right for you is to test it for several weeks. The proof will be in whether it fits with your lifestyle and if you lost weight.

Consumer Reports said that if you find a diet is too difficult to follow or isn't producing results, switch to another one.

The magazine also advises dieters to choose high-bulk, low-calorie foods such as fruits, veggies, soups and other water-filled foods. The authors also suggest controlling blood sugar by staying away from refined flour and eating plenty of high-fiber carbs, such as whole grains, fruits and veggies.