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SlimFast Diet Review: Does It Work for Weight Loss?

Written by Melissa Mitri, MS, RD

Reviewed by Ana Reisdorf, MS, RD 

Published on February 17, 2021

Dietitian Rating:


About This Rating
The average rating of this product is calculated based on the evaluation of the following factors:
  • Evidence-Based:2.0
  • Easy to Follow:4.0
  • Customization:3.0
  • Sustainability:3.0
  • Safety:3.0
  • Value for the Price:2.0
  • Accountability:2.0

SlimFast Diet is not recommended as a way to lose weight because it involves processed meal replacements and is not sustainable.

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SlimFast Diet Review: Does It Work for Weight Loss?


  • Convenient
  • No thinking required
  • Encourages portion control
  • Resources and tips provided by a registered dietitian


  • Not sustainable long-term
  • Doesn’t teach you how to eat
  • Processed products
  • Not satisfying like real food

How the SlimFast Diet Works

SlimFast is a weight loss program based primarily on meal replacement shakes, bars, and snacks.

It has been around for a while, and almost all of my clients have tried it at some point in their weight loss journey.

The SlimFast diet protocol requires 2 of your 3 meals to be one of their products – such as protein shakes, bars, or “fat bomb” snacks. Your third meal should be a “sensible” portion of real food.

It is also recommended to have 3 snacks per day, such as their SlimFast products or other low-calorie healthy snacks.

As a SlilmFast member, you have access to recipes you can use for that third meal.

In looking at the recipes, some are fairly healthy and nutritious, while others are loaded in sodium. This can make it hard to eat a healthy meal consistently.

Here is a daily sample menu on SlimFast Diet:

  • Breakfast: SlimFast Vanilla Cream Shake
  • Snack: 100-calorie SlimFast chips
  • Lunch: SlimFast Chocolately Peanut Butter Pie Bar
  • Snack: 1-ounce almonds
  • Dinner: One-Sheet Baked Chicken Fajitas (SlimFast recipe)
  • Snack: 1 portion SlimFast Keto Fat-Bomb Snack Crisps

SlimFast also has a maintenance program where you are advised to eat two sensible real meals a day plus one SlimFast meal replacement.

SlimFast Diet’s Scorecard

The SlimFast Diet was objectively evaluated by a dietitian based on the following criteria:

Evidence-Based: 2/5
Easy to Follow: 4/5
Customization: 3/5
Sustainability: 3/5
Safety: 3/5
Value for the Price: 2/5
Accountability: 2/5
Overall Rating: 2.7/5

Foods to Eat and Avoid

There are no foods that are off-limits on SlimFast. Calorie recommendations range from about 1200–1600 calories per day.

Snacks should not be more than 100 calories, and your meal should not exceed 500 calories.

You can choose 4 different product plans based on your preference – original, keto, diabetic, and favorite foods.

Can It Help You Lose Weight?

There are a few studies available on meal replacement programs and weight loss, but not specifically on SlimFast.

The majority of the research says meal replacement programs like SlimFast can help you lose weight in the first few months, but they are not sustainable.

As a registered dietitian specializing in weight loss, I do not recommend meal replacements as a good way to lose weight.

Meal replacements are often a seemingly easy temporary fix that doesn’t really teach you how to eat properly.


The SlimFast program is initially pretty easy to follow because it takes the guesswork out of eating.

Because two out of your three meals are SlimFast products, you only have to worry about preparing dinner. For some people, this is very appealing.

However, it doesn’t really teach you how to eat in the long-term or create healthier habits.

It also can get monotonous eating shakes and bars for the majority of your meals.

Once you get bored with it, you will likely go back to eating normally, gain the weight back, and need more guidance.

The cost of having to buy the products can also be a factor in remaining on this diet long-term.


After purchasing a SlimFast plan, you get access to a private Facebook group.

There is also a registered dietitian available as a consultant who provides educational videos and meal ideas.

However, there is no individualized guidance or accountability, and the dietitian is not available for 1:1 support.

Accountability is one of the biggest benefits of a weight loss program as it keeps you on track and supported.

For someone who wants a more personalized plan for their needs and lifestyle, I would not recommend SlimFast.

Value for the Price

The cost is over $100 per month for 2 SlimFast products per day.

The products themselves are fairly similar in price to the average meal replacement, but they contain many additives, artificial sweeteners, and added sugars, depending on the product.

I would not consider the price a good value because the products are processed and are not satisfying.

I used to drink SlimFast shakes after having my second child because they were quick and easy.

But even those that were higher in protein did not fill me up. I was starving an hour later, leading me to want to eat more.

If you are going to drink a meal replacement, it needs to be something that will be more satisfying. Otherwise, it’s not really serving its purpose.


Those with food allergies to milk, soy, or peanuts should not have SlimFast products, as many of their products contain these ingredients.

One thing I noticed is that saturated fat is not listed on the nutrition label of SlimFast products. I thought this was odd, as this is always present on a label.

The total fat content is fairly high, and so I wonder if they do not list the saturated fat intentionally.

I would also not recommend SlimFast to anyone with a history of disordered eating, as it is a diet product and may trigger eating disorder behaviors.

How It Compares

The price of the SlimFast program is higher than other commercial weight loss programs like Jenny Craig or Weight Watchers.

Some of this is because of the requirement to purchase their products.

However, SlimFast is more flexible as it doesn’t require a long-term commitment. You can try it for a month without any associated fees if you cancel.

Most other weight loss programs require a subscription and charge a fee if you want to opt-out.

The biggest difference between SlimFast and other programs is that there are more meal replacements than real food.

However, according to most health professionals, including myself, meal replacements are not as nutritious or satisfying as real food.

The Bottom Line

While the SlimFast Diet can result in initial short-term weight loss, it is not sustainable. It’s not realistic to say you’re going to eat bars and shakes your whole life.

Once people stop following it, the weight is often regained. I’ve seen this in essentially all of my clients who have come to me after following it. They want real food!

Instead of SlimFast, I would suggest eating a lower-calorie, balanced diet with real food that is satisfying.

Learning how to prepare healthy meals are skills you can use for life.

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