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The Promise

The Slimfast of today is different than you may remember: Gone are the days of shakes alone. The plan promises you can drop pounds with tasty snacks, meal replacements (shakes or bars), and one sensible meal a day.

Slimfast calls it the “3-2-1 Plan.” Every day, you eat two Slimfast meal replacements, three 100-calorie snacks (Slimfast snack bars, fruits, veggies, or even nuts), and one 500-calorie meal that you provide.

The program says you can lose a safe 1 to 2 pounds per week with this strategy.

What You Can Eat and What You Can't

Meal replacements include six flavors of 200-calorie protein meal bars, 8 pre-made protein meal shakes, and six flavors of powdered protein shake mixes (to be mixed with skim milk).

For 100-calorie snack options, choose among four different Slimfast snack bars, including peanut butter crunch and double-Dutch chocolate, or fruit (an orange, cherries, banana, grapes, or pear), carrot sticks, pistachios, pretzels, sorbet, or nonfat yogurt.

For the meal you provide, Slimfast recommends filling half of your plate with vegetables (such as green beans, carrots, eggplant, spinach, or broccoli); a quarter with lean protein (beef, poultry, pork, tofu, or fish); and the remaining quarter with starch (whole wheat pasta or bread, brown rice, potatoes, or corn).

Nothing is totally off-limits with Slimfast, including alcohol. The Slimfast web site features recipes for alcoholic and nonalcoholic drinks made with its shakes.

Level of Effort: Medium

You'll need Slimfast’s snack bars, meal bars, and shakes for most of your food, but you have some flexibility for the meal that you provide.

Limitations: Slimfast’s selection of meal replacement bars and shakes is limited to about 20. You have more flexibility with snacks and with the meal you provide, which includes lean protein, vegetables, and a starch.

Cooking and shopping: Snack bars, meal replacement bars, and shakes are grab-and-go. You only plan and prepare one meal a day, which cuts down on trips to the grocery store.

Packaged foods or meals: Required.

In-person meetings: None.

Exercise: Daily exercise, including walking and strength training, is encouraged. The program doesn’t offer a specific workout plan.

Does It Allow for Dietary Restrictions or Preferences?

Vegetarians and vegans: Vegetarians on the 3-2-1 Plan can have 4 to 6 ounces of a meat alternative, such as quinoa, tofu, lentils, or black beans, for their daily meal. Reduced- or low-fat dairy (yogurt, milk, cheese) is also OK. Vegans have fewer options, since most meal replacements are made with dairy or eggs, which aren't part of a vegan diet.

Gluten-free: The Slimfast products are not labeled with regards to gluten, so check the ingredients list for possible sources of gluten, and contact the company if in doubt.

Lactose-intolerant: If you have problems digesting lactose, you can combine Slimfast shake mixes with lactose-free milk or low-fat soy milk. Slimfast meal bars have 2 grams of lactose or less per serving.

What Else You Should Know

Cost: Slimfast products are sold in grocery stores and drugstores. At one online discount grocer, a 30-day supply of six boxes of meal bars, five boxes of snack bars and 32 shake mixes costs $75, plus shipping. A five-pack of meal bars runs about $4.88; a six-pack of snack bars is $3.25; an eight-pack of pre-made shakes is $9.88; and a carton of protein powder shake mix is $8.

Support: You can submit questions to Slimfast's online dietitian. Connect with other dieters on the company’s Facebook page and a Pinterest-like program called Slimfast Translator. The Slimfast web site includes meal and drink recipes, and you can sign up to get monthly emails featuring recipes, exercise and weight-loss tips, and coupons.

What Brunilda Nazario, MD, Says:

Does It Work?

Yes, Slimfast works for weight loss. Structured programs, like this one, work for people who don't want to count calories. Studies show that people lose more weight when they eat portion-controlled meals or meal replacements.

Low-calorie diets, such as the Slimfast diet or the use of one or two meal replacements, promote weight loss and can help you keep it off longer.

Is It Good for Certain Conditions?

Conditions such as diabetes, high cholesterol, and high blood pressure are driven by extra weight, so cutting calories must be part of their treatment.

Anyone looking to lose weight on a calorie-restricted diet should work with a nutritionist or their doctor. Since the fastest weight loss happens during the first few weeks of dieting, your doctor may need to adjust any drugs you take, such as insulin or blood pressure medications.

Weight loss can make your blood sugar levels drop. Dizziness, fatigue, and other symptoms of low blood sugar may mean you need to check your blood sugar levels more often.

The Final Word

This diet works very well for weight loss. One of its major highlights is calorie restriction through meal replacement -- and this works for maintaining weight, too. Losing weight may be the easiest part of dieting. Sticking with a lifelong plan and keeping the weight off is where meal replacements like Slimfast shine.

One downside to consider is that there are no in-person meetings. So dealing with relapses and solving issues that happen on a day- to-day basis might be something that you can address in online communities.

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