What Is the SlimFast Diet?


Verywell / Debbie Burkhoff 

The SlimFast diet plan consists of meal-replacement shakes and bars sold at grocery and drug stores. The diet and its products have evolved over the years to offer more variety to help people lose weight.

Many people have had success with short-term weight reduction using SlimFast (or other shake diets such as Herbalife), which is an easy-to-follow low-calorie plan. However, it is not recommended as a long-term diet.

What Experts Say

"Diets that promote eating bars and shakes instead of real foods aren't sustainable and often aren't healthy. You might lose weight, but replacing your meals with highly processed meal replacements won't deliver long-lasting, satiating results."

Kelly Plowe, MS, RD


The SlimFast diet was founded in 1977 as a diet shake line. The initial shakes came in chocolate, vanilla, and strawberry. The diet plan was a shake for breakfast and lunch, followed by a sensible dinner.

During the 1990s, SlimFast expanded its line to include meal replacement bars. As low-carb diets came into fashion in the mid-2000s, the company launched low-carb and low-sugar alternatives with SlimFast Optima product. In 2009, SlimFast updated its program again to the 3-2-1 plan which included three snacks, two meal replacements (shakes or bars), and one dinner.

How It Works

The current SlimFast diet plan calls for eating six times a day. Here are is an example of how it works.

  • One full meal of your choice (500 calories for women, 800 calories for men)
  • Two shakes or smoothies
  • Three 100-calorie snacks

You can purchase SlimFast snacks or make your own snacks at home. The plan allows you to eat out for your main meal or cook at home. You can enjoy alcohol in moderation, but it's recommended to limit alcohol consumption.

According to SlimFast, women on the diet consume approximately 1,200 calories per day on the plan and men consume 1,600 calories per day. This allows for weight loss at a safe rate of approximately 1 to 2 pounds per week.

What to Eat

The main focus of the SlimFast diet is its shakes, which come in a variety of formulas and flavors. The newer Advanced Nutrition Shakes and Smoothies provide more protein and less carbohydrate than the original shakes. Here's a closer look at the nutritional makeup of the different SlimFast shakes:

  • Original SlimFast Chocolate Royale Shake Mix contains190 calories, 4 grams fat, 1 gram saturated fat, 30 grams carbohydrate, 4 grams fiber, 22 grams sugar, 10 grams protein. The primary (first) ingredient in Original SlimFast Chocolate Royale shake mix is sugar followed by sunflower oil, cocoa and other ingredients. Other flavors of Original SlimFast Shake Mix have a similar, but not identical, nutrition profile.
  • Original SlimFast Rich Chocolate Royale Shake (Pre-Made) contains180 calories, 5 grams fat, 1 gram saturated fat, 24 grams carbohydrate, 5 grams fiber, 19 grams sugar, 10 grams protein. The primary ingredient in Original SlimFast Chocolate Royale shakes is fat-free milk, followed by water, sugar, oil, and other ingredients. Other flavors of Original SlimFast Shakes are similar in nutrition.
  • Advanced Nutrition SlimFast Creamy Chocolate Smoothie Mix is mixed with eight ounces of skim milk and contains 190 calories, 3 grams fat, 0.5 grams saturated fat, 19 grams carbohydrate, 5 grams fiber, 13 grams sugar, 20 grams protein. The ingredients include whey protein isolate, soy protein isolate, cocoa, sunflower oil, thickeners, and sweeteners.

If you compare the ingredients and nutrition for these products with a typical smoothie that you make at home from scratch with fresh fruit, fiber-rich seeds, and other healthy ingredients, you're likely to be disappointed. It would be unusual to find oil or artificial sweeteners in most traditional smoothie recipes.

But many people who buy SlimFast enjoy the convenience of the products. Making a nutritious smoothie away from home is usually not an option.

Compliant Foods
  • SlimFast shakes, snacks, and meal bars

  • One "sensible" meal a day

  • Alcohol

  • Coffee

Non-Compliant Foods
  • No foods are explicitly banned on the SlimFast diet, but calories are restricted


On the SlimFast plan, you will eat six times a day. Replace any two meals with a SlimFast shake, eat one portion-controlled meal a day, and enjoy three 100-calorie snacks in between.

The diet centers around SlimFast products, which are formulated so people can lose weight successfully on the program. The shake lines come in regular, low-sugar, and high-protein varieties.

The 100-calorie snack packs are part of SlimFast's Advanced Nutrition program. There are a wide variety of foods to choose from so you're likely to find something to satisfy your sweet or salty cravings. For example, you can buy savory Sour Cream and Onion Baked Chips when you want something salty and Cinnamon Bun Swirl Drizzled Crisps when you need to satisfy your sweet tooth.

Nutrition facts vary for each snack, but each flavor provides both protein and fiber. You're likely to feel satisfied after eating (and eat less as a result) when you fill up on foods with fiber and protein.

Pros and Cons

Like all diet plans, SlimFast has both benefits and drawbacks.

  • Easily accessible

  • Less expensive than other commercial plans

  • Easy to follow

  • Portion controlled

  • Heavily processed food

  • Does not teach healthy eating skills, like portion control, calorie counting, or low-calorie cooking

  • No face-to-face support

  • Taste


  • Provides easy accessibility: You'll find the products in almost every supermarket, grocery store, and pharmacy around the country. You also can find the products online.
  • Costs less: Some diet plans, like Jenny Craig, Nutrisystem, and Weight Watchers require you to commit to a longer-term program in order to get the lowest price. SlimFast requires no commitment at all. You can try it for a day or a week or a month without having to cancel a subscription meal service or plan.
  • Offers easy-to-follow instructions: No foods are off limits and portion control is built in when you buy the packaged snack products. In addition, one meal per day that you enjoy allows you to consume more calories than some other diets that recommend 300 or 400 calorie meals.
  • Provides built-in calorie counting: There is no need to download an app, keep a journal, or log foods. Almost all of the math is done for you, except for the one daily meal.
  • Encourages exercise: However, no formal program is provided. Some scientific studies have demonstrated successful weight loss with meal replacement programs like SlimFast, although many of the studies included guided support or education programs as part of the trial.


  • Contains processed foods: The program is built primarily on processed foods. Most health experts recommend that you decrease the amount of processed food that you consume and increase your intake of fresh or frozen fruits and vegetables, lean meats, seafood, and whole grains for optimal health.
  • Limits healthy cooking: You may not learn healthy cooking methods on the SlimFast diet plan. Cooking is not required on the program. And since you are able to consume a hearty 500 to 800 calories at your main meal, you could easily eat out or buy more processed food.
  • Disregards portion control: If you reach your goal weight on the SlimFast diet, you're going to have to eventually wean yourself off the program and maintain your weight loss. Because the diet products are already portion controlled, you may not develop the skills you need to make it through this important transition without weight gain.
  • Offers no maintenance plan: Once you reach your goal weight, you are advised to slowly decrease your use of SlimFast and increase your intake of typical foods. But beyond that, there is no structured plan that weans you completely off the products. If you get used to eating junk food on the diet, you may be tempted to eat these foods after the diet is complete and gain back the weight.
  • Provides no personalized support: However, the program does offer a Facebook page and recipes on the website. Many large diet forums (like SparkPeople) have groups dedicated to those following SlimFast.
  • Lacks a quality taste: The taste of SlimFast shakes has been criticized online, but it's important to keep the reviews in perspective. Consumers are often more highly motivated to post online reviews if they don't like a product. But to stay on the safe side, you might want to invest in just a few products until you are sure that you enjoy them sufficiently to stay on the diet long enough to reach your goal.

How It Compares

The SlimFast diet plan has a 30-year track record of helping people to lose weight successfully in the short-term. Many people who have used SlimFast do so to reach a quick, short-term goal, such as an upcoming event they want to slim down for.

However, it isn't a long-term weight loss solution or a healthy eating plan. The diet does not teach skills, like healthy meal planning and preparing, needed for sustained weight loss.

The 2019 U.S. News and World Report Best Diets ranks the SlimFast diet number 27 in Best Diets Overall and gives it an overall score of 2.9/5.

Its ranking is based on its high marks for short-term weight loss and diabetes prevention and management, and low marks for nutrition, heart-health, and long-term sustained weight loss.

USDA Recommendations

The U.S. Department of Agriculture (USDA) dietary guidelines provide recommendations for a healthy, balanced diet. The following nutrient-dense foods are considered part of a healthy diet:

  • Beans and legumes (all beans, lentils, peas)
  • Dairy (reduced fat milk, cheese, yogurt)
  • Fruits (apples, berries, melon)
  • Grains (quinoa, brown rice, oats)
  • Lean meats (chicken breast, fish, turkey breast)
  • Nuts and seeds (walnuts, almonds, sunflower seeds)
  • Oils (olive oil, avocado oil) 
  • Vegetables and dark, leafy greens (kale, spinach, broccoli, Swiss chard, green beans)

As a meal-replacement diet, SlimFast does not meet the USDA's definition of a healthy meal plan. The USDA recommends consuming roughly 1,500 calories per day for weight loss, but this number varies based on age, sex, weight, and activity level. Use this calculator to determine the right number of calories for you.

Similar Diets

Here's how the SlimFast diet compares to similar meal-replacement plans like Jenny Craig and Nutrisystem.


  • Accessibility: Products can be purchased at your local grocery or drug store.
  • Cost: An 11-ounce container of SlimFast protein powder makes 12 servings and retails for around $10.
  • Types of Food: The SlimFast diet replaces two meals with SlimFast shakes, bars, or cookies, three 100-calorie snacks in between meals, and one regular meal a day.

Jenny Craig

  • Accessibility: Meals must be ordered online or picked up from a Jenny Craig diet center.
  • Cost: The meal plan ranges from $15 to $23 a day, plus shipping. A month's worth of food can cost between $550 and $800.
  • Types of Food: All meal entrées are all frozen and need to be heated. Many people on the plan say it's one of the best-tasting heat-and-eat meal services on the market.


  • Accessibility: Products are ordered online or by phone. Wal-Mart also carries some Nutrisystem products
  • Cost: A one-time delivery of a four-week meal plan costs between about $455 and almost $680 depending on the selected plan.
  • Types of Food: Three meals and up to two snacks each day comprise real food such as waffles with scrambled eggs and coffee, low-fat string cheese with carrot sticks, and grilled chicken sandwich with a side salad.
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Article Sources
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