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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.

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 any of these products. All information presented is purely research-based and was correct at the time of publication.

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

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

SlimFast states that it has “40+ years of proven weight loss success.” Reviews are mixed, however, depending on the source.

More positive reviews generally say that products are convenient, flavorful, and lead to initial weight loss. Less positive reviews reflect that it can be difficult to stick to the diet in the long term, making it difficult to maintain weight loss.

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

A person can choose from one 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, their diet 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.

Two 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.

Three 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.

The app offers:

  • 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

A person can sign up on SlimFast’s website or download the company’s Together app from GooglePlay 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 with vegan diets, however — 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:

Some sample lunch and dinner recipes include:

Some sample 100-calorie snacks include:

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.

Learn more about SlimFast meals and recipes here.

SlimFast does not offer a subscription service. The cost depends on where a person buys their groceries, what they buy, and which SlimFast products they choose.

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 on the company’s shakes alone.

The Together app is free to download.

The SlimFast diet involves restricting the intake of calories. When a person burns more calories than they consume, it typically leads to weight loss.

According to one 2006 review of studies on weight loss, low calorie diets can reduce body weight “by an average of 8% in the short term.” The researchers note that people who follow low calorie diets tend to tolerate them well and that these diets can play a role in maintaining significant weight loss over 5 years.

However, low calorie diets and other restrictive diets remain controversial. In a 2018 study, researchers concluded that the best diets involve realistic goals and account for each person’s preferences, needs, and any medical conditions.

SlimFast’s products tend to be rich in protein, with each shake containing 10–20 g, for example. Protein may play an important role in weight loss. One 2016 meta-analysis found that consuming protein increased feelings of fullness, which may reduce cravings and help with weight loss.

Studies on SlimFast

Research into the SlimFast plan indicates that it can promote weight loss. However, other weight loss programs may be just as effective.

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

According to one 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 were affiliated 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 older 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

Some evidence suggests that losing weight through calorie restriction can improve insulin sensitivity, which reduces the risk of developing type 2 diabetes.

One 2001 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 the 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. 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 2015 study indicates that people with a varied diet are less likely to have obesity.

There are several alternatives to SlimFast, including:

  • OPTIFAST: This 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.

Learn more about weight loss meal plans here.

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 dietician, who can help tailor a weight loss plan to suit their lifestyle and medical needs.

Learn more about losing weight here.

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.