Does Slim Fast Work

SlimFast has an A+ rating with the Better Business Bureau (BBB), although SlimFast is not an accredited brand.


photo of woman drinking from can

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

With the Slimfast plan, 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. With this plan you can eat 6 times per day.

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

They also offer products called Slimfast Advanced Nutrition that provide high-protein meal-replacement shakes or smoothies with less sugar than many other brands. They have more protein than the original Slimfast products. The advanced plan also offers 100-calorie snacks and meal replacement bars.

What You Can Eat and What You Can’t

Meal replacements include a variety of flavors in their original and advanced protein meal bars, premade protein meal shakes, and powdered protein shake mixes (to be mixed with skim milk). In 2020, the company reformulated its drinks.

For 100-calorie snack options, choose from a variety of flavors from their original Slimfast snack bars or from the Slimfast Advanced Nutrition snacks.

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 website 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 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 meal-replacement shakes and smoothies are labeled gluten-free. Other products are not labeled with regard 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. Slimfast Advanced Nutrition meal-replacement shakes are lactose-free.

What Else You Should Know

Cost: Slimfast products are sold in grocery stores and drugstores. Packages range from $9.99 to $89.99.

Support: You can submit questions to Slimfast’s online dietitian. Slimfast’s Facebook page offers dieters a way to connect with each other and offer advice. The Slimfast website 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 can work 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 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 and Slimfast Advanced Nutrition shine.

One downside is that there are no in-person meetings. So dealing with cheating on your diet and solving problems that happen day to day might be something that you can address in online communities.

SlimFast reviews: Do shakes for weight loss work?

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The SlimFast plan is a weight loss diet. It involves having two meal replacement shakes, one calorie-controlled meal, and three low calorie snacks daily.

SlimFast shakes lined up over green background next to SlimFast logo

This article looks at the potential benefits and risks of the SlimFast plan. It also provides information about menu options and some alternative products.

Please note that the writer of this article has not tried these products. All information presented is purely research-based and correct at the time of publication.

Medical News Today follows a strict product selection and vetting process. Learn more here.

SlimFast initially launched in 1977 as a line of meal replacement shakes.

The company eventually expanded to offer snacks and products specifically for people with diabetes or those following a ketogenic diet.

SlimFast states it has “40+ years of proven weight loss success.” However, depending on the source, buyers give the company mixed reviews.

More positive reviews generally say that products are convenient, flavorful, and lead to initial weight loss.

Less positive reviews say that it can be challenging to stick to the diet in the long term, making it difficult to maintain weight loss.

The company offers a range of products and services from its website and mobile app.

These include meal planning, meal replacement shakes and snacks, goal tracking, and the ability to generate grocery lists from meals and recipes.

A person may wish to consider the pros and cons of SlimFast, which may include:


  • may be suitable for short-term weight loss
  • plan is easy to follow
  • many products are gluten-free
  • SlimFast app helps people incorporate exercise and healthy lifestyle choices
  • subscription plans offer approximate savings of 12%
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  • may not work for long-term weight loss
  • plan can be too restrictive long-term
  • expensive
  • some products are high in fat
  • meal replacement products may not contain sufficient calories

The SlimFast plan has a three-step structure that includes meals, replacement shakes, and snacks.

A person can choose from one of the following types of plans:

  • Favorite Foods: This includes one meal a day and snacks based on preferences. There are no limits to the types of foods a person can eat, as long as they stay within the recommended range of calories.
  • Low Carb: This plan includes foods that have below-average carb counts. A person can have a combination of homemade and packaged meals and snacks.
  • Keto: This includes a variety of keto-friendly shakes, meals, and snacks.
  • SlimFast Original: This is the company’s original diet plan, and it includes snacks, meals, and shakes.

Regardless of a person’s choice, the SlimFast plan typically involves:

One 600-calorie meal

No foods are off-limits, as long as the meal falls within the total recommended number of calories. Depending on a person’s preference, this meal may be keto, low carb, or vegetarian, for example.

SlimFast states that males should add 200 calories to each meal replacement daily.

To help with meal planning, a person can find sample recipes on the SlimFast website.

2 replacement shakes

A person can buy their shakes as mixes or ready-to-drink products. Among the many flavors are strawberry, chocolate, vanilla, and cappuccino.

According to the company, each SlimFast shake contains 24 essential vitamins and minerals, along with 4–5 grams (g) of fiber and 10–20 g of protein, depending on the type a person chooses.

3 snacks between meals

SlimFast offers a range of sweet and savory snacks.

Some are designed for ketogenic or diabetes-friendly diets. For example, the keto options include trail mixes, Cheddar Cheese Crisps, and bars.

Overall, anyone following a SlimFast plan should drink plenty of water and exercise for 30 minutes a day.

Once a person has reached their target weight, they can move to the SlimFast maintenance plan.

This involves replacing one meal a day with a SlimFast shake or snack, eating two sensible meals of choice, and snacking between meals.

SlimFast Together

A person can download the SlimFast Together app for free on Google Play or the App Store.

  • a quiz to help people find the best plan for them
  • tools to help plan and customize meals, including a calorie and macro calculator
  • a recipe search function
  • the option of purchasing SlimFast products in-app
  • an automatically generated grocery list for pick-up or delivery
  • tools for tracking weight loss, water intake, and physical activity

SlimFast is for people who would like to lose weight quickly. It may not be suitable for people who want to lose weight sustainably over a longer period of time.

It may also be helpful for people who do not have a lot of time to incorporate a new diet into their routine.

SlimFast typically asks people to replace two of their meals with SlimFast products. This means a person may only need to cook one meal a day, which can save time and make the plan easier to follow.

It allows individuals to easily access recipes, create meal plans, track progress, and purchase products that can help busy people work toward their weight loss goals.

However, SlimFast is not suitable for people working with smaller budgets. Some people may also find the SlimFast plan too restrictive over the long term.

SlimFast has an A+ rating with the Better Business Bureau (BBB), although SlimFast is not an accredited brand.

It has a review rating of 1 out of 5 stars based on just 4 reviews. However, these reviews are about SlimFast’s parent company, Unilever, and are not specific to the SlimFast brand.

On Trustpilot, SlimFast has just one review and an overall rating of 3.2 out of 5. The company has not claimed this profile or responded to complaints.

A person can sign up on SlimFast’s website or download the company’s Together app from Google Play or the App Store.

Signing up involves providing basic contact information, including an email address and a physical address.

Next, a person answers questions designed to direct them toward the right plan for them. Regardless of the company’s recommendation, a person can choose the plan they like the best.

On the company’s website, as well as its app, a person can:

  • record their meals, exercise, and water intake
  • order SlimFast products
  • create meal plans
  • view recipes
  • shop for ingredients from local stores
  • track their progress

According to SlimFast, their plan works for people with low carb, keto, high protein, diabetes-friendly, and vegetarian diets. There are not many options for people following vegan diets, though, as most meal replacements contain dairy or eggs.

The shakes and smoothies are labeled gluten-free, though some of the other products may contain gluten.

Individual SlimFast products are available for purchase online.

Recipe ideas

Some sample breakfast recipes, from the company’s website, include:

  • oatmeal and Greek yogurt with berries
  • French vanilla blackberry pancakes
  • a grilled veggie omelet
  • avocado egg-in-a-hole

Some sample lunch and dinner recipes include:

  • baked chicken fajitas
  • sweet potato and black bean burgers
  • baked cod with asparagus and tomatoes
  • one-pot sausage, kale, and sweet potato pasta

Some sample 100-calorie snacks include:

  • keto chocolate fudge
  • chocolate almond bark
  • crispy Parmesan garlic edamame
  • cucumbers and cream cheese

For the one daily meal, SlimFast recommends allocating half of the plate for vegetables, a quarter of the plate for lean protein, and a quarter of the plate for starches.

While no foods are off-limits, opting for the following can make it easier to stay within the calorie allowance:

  • whole grains, such as brown rice, quinoa, buckwheat, oatmeal, bulgur, and millet
  • lean proteins, such as salmon, chicken, turkey, white fish, lean beef, tofu, and legumes
  • vegetables, and a person can choose any
  • fruits, and a person can choose any

A person can also opt for any nuts and seeds, though keeping an eye on portion size is important.

SlimFast allows for alcohol in moderation. If a person has a serving of alcohol, the company recommends removing one snack from the diet for that day.

The cost depends on where a person buys their groceries, what they buy, and which SlimFast products they choose.

A subscription service is available, allowing customers to receive their products on a schedule and save around 12% of the overall costs.

However, a four-pack of shakes starts at $9.99. This means that a person following a SlimFast plan can expect to pay around $140 each month for the company’s shakes alone.

The Together app is free to download.

The SlimFast diet involves restricting calories, which is one of the most important factors in weight loss, according to a 2021 research review of different weight loss methods.

With SlimFast, a person reduces their calories by replacing meals. The authors of this study write that meal replacements can be useful for people who find it difficult to estimate the calorie content of their food.

The authors also write that low calorie diets can reduce body weight in the short term.

However, they concluded that while meal replacement diet plans are convenient, they do not work for maintaining weight loss over a long period of time.

Additionally, this study suggested that weight loss and maintenance should be individualized, as the authors did not find one particular best strategy for weight loss in the studies they reviewed.

As SlimFast provides a set plan that cannot easily be individualized, the results of this study suggest that SlimFast may not be suitable for long-term or significant weight loss.

This is reflected in earlier 2018 research , in which the authors concluded that the best diets for people with obesity and overweight involve realistic goals and account for each person’s preferences, needs, and medical conditions.

That said, SlimFast products can have a high protein content, with shakes containing 10–20 g of protein. Protein may play an important role in weight loss. The 2021 research review points out that consuming protein increases satiety, which may encourage people to eat less during meals.

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Studies on SlimFast

Current research into the SlimFast plan is extremely limited, but older studies indicate that it can promote weight loss. However, other weight loss programs may be just as effective.

An older 2006 study that compared SlimFast with the Atkins diet, the Weight Watchers Pure Points program, and the “Eat Yourself Slim” plan found that all participants reported significant — and comparable — losses in weight and body fat over 6 months, compared with the control group. All the participants had overweight or obesity at the beginning of the study.

A smaller 2004 study of 63 people with obesity found that following the SlimFast plan for 6 months led to an average 7% body weight loss.

According to a 2003 review of six randomized controlled trials of SlimFast and similar meal replacement programs, these plans can safely and effectively lead to significant, sustainable weight loss. However, several of the researchers involved had affiliations with SlimFast.

Some research indicates that SlimFast may help adolescents with obesity lose weight in the short term. However, the team found that this plan may not help adolescents maintain weight loss.

It is important to note that these studies typically involve participants with overweight or obesity. Therefore, it is difficult to know how effective the SlimFast plan might be for people with more moderate weights.

In addition, many of these studies are almost 20 years old and may not reflect current weight loss strategies.

Below, we explore some risks and potential benefits of the SlimFast plan in more detail.

Possible benefits

A 2021 study suggests that weight loss through calorie restriction can improve insulin sensitivity, which reduces the risk of developing type 2 diabetes.

One 2018 study found that meal replacement shakes can be a safe, effective way for people with obesity and type 2 diabetes to lose weight and improve their glucose, insulin, and lipid levels.

Restricting calories while making other recommended lifestyle changes may also improve heart health and prevent cardiovascular events in people with overweight or obesity.

In addition, some research indicates that the SlimFast plan leads to cholesterol changes that may reduce the risk of cardiovascular disease.

Risks and disadvantages

One downside of meal replacement plans is that maintaining weight loss can be difficult over long periods.

However, at least one older study suggests that meal replacement plans are easier than other weight loss programs. This may mean that some people find them easier to stick to in the long term.

SlimFast may provide less support than other dietary plans, and if a person goes back to their past eating habits, they may regain some or all of the weight that they lost.

Also, for many people, the cost of SlimFast products is prohibitive, especially in the long term.

For instance, a four-pack of shakes starts at $9.99, and a person would need about 3.5 packs a week in order to have two shakes a day.

That works out to $139.86 a month just for the shakes. A person then needs to account for snacks and food for the meal each day.

Another downside is that the diet may become repetitive and boring. It focuses on calorie restriction, but the company does not teach healthy eating habits or the importance of consuming a variety of nutrient-rich foods.

In addition, the SlimFast plan relies on heavily processed foods.

One 2021 study indicates that people with a Mediterranean, low carb, high protein, or keto diet are less likely to have obesity.

The table below details how SlimFast compares with its competitors.

SlimFast Noom Atkins
Products offered • meal replacement shakes
• smoothies
• bars
• snacks
weight loss coaching app • frozen meals
• bars
• shakes
• chips
Meal planning and goal tracking yes yes yes
Subscription available yes yes yes
Mobile app yes yes yes
Free shipping for orders above $99 service does not ship products for orders above $99
Trustpilot reviews 1 60,215 4
Trustpilot score 3.2 4.3 2.9
BBB reviews 4 627 0
BBB rating 1 1.29

There are several alternatives to SlimFast, including:

  • OPTIFAST: OPTIFAST includes a full meal replacement diet and a medically supervised plan.
  • Other meal replacement shakes: These are available in health stores, pharmacies, and supermarkets.
  • DIY shakes: A person can make these at home with protein powders, yogurts, seeds, nuts, fruits, vegetables, and other ingredients.

Anyone who wants to buy protein and meal replacement shakes should purchase them from a reputable brand. A 2010 Consumer Reports analysis found that some protein drinks contain unsafe levels of mercury, arsenic, and other contaminants.

The advocacy group Clean Label Project ran a study published in 2022 that tested 130 popular protein powders. It found that the products tested positive for a wide range of harmful substances, including:

  • arsenic
  • cadmium
  • lead
  • mercury
  • bisphenol A (BPA)
  • mycotoxins
  • pesticides
  • residual solvents

Traditional methods of weight loss, such as restricting calorie intake or intermittent fasting, may also be effective in the short term.

A person may benefit most from working with a personal trainer and registered dietitian, who can help tailor a weight loss plan to suit their lifestyle and medical needs.

The SlimFast plan may lead to significant weight loss for some people, at least in the short term. However, sustaining the results may be difficult.

Also, SlimFast products can be prohibitively expensive, especially in the long term.

Restricting calories and portion sizes, and receiving exercise and dietary tips from healthcare professionals and expert sources may be just as effective.

Last medically reviewed on October 2, 2022

How we reviewed this article:

Medical News Today has strict sourcing guidelines and draws only from peer-reviewed studies, academic research institutions, and medical journals and associations. We avoid using tertiary references. We link primary sources — including studies, scientific references, and statistics — within each article and also list them in the resources section at the bottom of our articles. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.

  • Bales, C. W., et al. (2013). Caloric restriction: Implications for human cardiometabolic health.
  • Berkowitz, R. I., et al. (2011). Meal replacements in the treatment of adolescent obesity: A randomized controlled trial.
  • Clean Label Project. (2022). Protein powder: Our point of view.
  • Guo, X., et al. (2018). Effects of a meal replacement on body composition and metabolic parameters among subjects with overweight or obesity.
  • Heymsfield, S. B., et al. (2003). Weight management using a meal replacement strategy: Meta and pooling analysis from six studies.
  • Huerta, S., et al. (2004). Feasibility of a partial meal replacement plan for weight loss in low-income patients.
  • Kim, J. Y. (2021). Optimal diet strategies for weight loss and weight loss maintenance.
  • Koliaki, C., et al. (2018). Defining the optimal dietary approach for safe, effective and sustainable weight loss in overweight and obese adults.
  • Morgan, L. M., et al. (2009). Comparison of the effects of four commercially available weight-loss programmes on lipid-based cardiovascular risk factors [Abstract].
  • Napoleão, A., et al. (2021). Effects of calorie restriction on health span and insulin resistance: Classic calorie restriction diet vs. ketosis-inducing diet.
  • Truby, H., et al. (2006). Randomised controlled trial of four commercial weight loss programmes in the UK: Initial findings from the BBC “diet trials.”

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Does Slim Fast Work

Medically reviewed by Kim Chin, RD, Nutrition — By Jayne Leonard and Stefano Iavarone — Updated on Oct 3, 2022

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Alex Koliada, PhD, is a well-known doctor. He is famous for his studies of ageing, genetics and other medical conditions. He works at the Institute of Food Biotechnology and Genomics NAS of Ukraine. His scientific researches are printed by the most reputable international magazines. Some of his works are: Differences in the gut Firmicutes to Bacteroidetes ratio across age groups in healthy Ukrainian population []; Mating status affects Drosophila lifespan, metabolism and antioxidant system [Science Direct]; Anise Hyssop Agastache foeniculum Increases Lifespan, Stress Resistance, and Metabolism by Affecting Free Radical Processes in Drosophila [Frontiersin].
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