Over more than 25 years, Slim-Fast has built a strong case for using meal replacements to lose weight. Multiple studies (some funded by Slim-Fast) show that sipping the company's shakes or nibbling on its nutrition bars can safely peel away pounds and keep them off. And to keep up with carb-phobic dieters, the company has introduced an Optima line-products for a new plan by the same name- that contains 55 percent less sugar than its original products. These lower-carb replacement drinks boast increased levels of protein and fiber, as well a whopping half-day's supply of calcium.

Rich Chocolate Brownie bars or a Banana Cream shake sound indulgent, but don't expect them to taste the same as offerings from a French bakery or the corner ice-cream parlor. They're not bad-just nothing to write home about. In fact, some nutritionists aren't keen about candy-like bars and sugary shakes standing in for meals. What's more, relying on these products doesn't teach dieters how to make healthful food choices on their own. Overall, Slim-Fast is a good system that works for many people, particularly because of the convenience. It's just not the tastiest way to shed pounds.

Basic principles:

The plan boils down to a time-tested strategy: Move more and eat less. Dieters eat one balanced meal a day and use Slim-Fast products-shakes, bars, soups, frozen pasta entrees-to replace two other meals. For snacks, you can choose conventional food or 130-calorie Slim-Fast snack bars (lighter than the meal-replacement bars, which pack 220 calories each). To get moving, you walk, jog, or do yard work for at least 30 minutes a day.

How the diet works:

This is a low-cal diet-obviously, meal replacements contain fewer calories than the average foods most folks eat. First, you purchase Slim-Fast products at the supermarket and use them for two meals a day and snacks. Then you eat one regular meal (600 to 700 calories) for breakfast, lunch, or dinner-your choice. An Easy Options Plan, outlined on product labels, provides more details. For further guidance, the company's Web site offers tips on everything from training for a 5K race to gaining the emotional support of family and friends.

What you can eat:

Slim-Fast shakes. Slim-Fast meal bars. Slim-Fast microwavable soups. Slim-Fast pasta entrees. And one meal a day that includes lean meat, starch, vegetables, and fruit. (Low-carb dieters can skip the starch and eat more veggies.) Between meals, you can choose from snack bars or healthful alternatives such as fruit, veggies, fat-free yogurt, nuts, pretzels, and air-popped popcorn. Fruit is the top choice for dessert, but you can occasionally substitute sugar-free puddings or sorbets.

Does the diet take and keep weight off?

Yes. Slim-Fast is one of the few diet companies to back up its products with the gold standard in diet research: controlled clinical trials. The latest findings, presented at the North American Association for the Study of Obesity in October 2003, show that people who used Slim-Fast on and off for 10 years to maintain their weight were on average 33 pounds lighter than a similar group who went without the meal replacements.

Is the diet healthy?

Yes. As long as you eat a balanced meal and snack on fruits, veggies, and other nutritious choices, the plan is sound. The Slim-Fast Web site urges dieters to consume at least 1,200 calories a day and lose no more than 2 pounds a week.

What do the experts say?

"I'm a very big advocate of meal replacements like Slim-Fast for weight control," says registered dietitian Dawn Jackson, a spokeswoman for the American Dietetic Association and a dietitian at Northwestern Memorial Wellness Institute in Chicago. Jackson has clients who've lost weight successfully with the plan, and she thinks meal-replacement products in general are a good way to learn about realistic portion sizes.

But Chris Rosenbloom, PhD, a professor of nutrition at Georgia State University, has mixed feelings. She says meal-replacement shakes and bars "may be fortified with vitamins and minerals, but just like a vitamin supplement, they're not going to provide you with everything you need." While Rosenbloom admits that Slim-Fast can help people lose weight, she prefers to see dieters work to keep the pounds off using whole foods.

Who should consider the diet?

Anyone who needs a lot of structure and prefers that someone else fix the meals. Folks who love to cook and enjoy fresh foods, though, may be turned off by the convenience-style products.

Bottom line:

Like other low-calorie, nutrient-dense eating plans, meal-replacement diets like Slim-Fast do have a good track record of helping people shed weight and keep it off. Keep in mind, though, that bars and shakes don't provide all the benefits of real food-so use caution when thinking long-term.
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