We include products we think are useful for our readers. If you buy through links on this page, we may earn a small commission. Here’s our process.

The SlimFast plan is a weight loss diet. It involves combining two meal replacement shakes with 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 on menu options and some alternative products.

Please note that the writer of this article has not tried any of these products. All information presented here is purely research-based.

SlimFast initially launched in 1977 as a meal replacement shake product line.

They later expanded to include branded snack products, alongside ranges specifically for those with diabetes and those following a ketogenic diet.

SlimFast state that the product line has “40+ years of proven weight loss success.” Reviews on their products are mixed, depending on the source.

Favorable reviews generally cite the product’s ease of use, flavor, and initial weight loss success. Less favorable reviews often state that it can be difficult to stick to the plan long term, making weight loss maintenance challenging.

The SlimFast plan is based on a three-step structure that involves consuming the following each day:

1. One 600-calorie meal

With this meal, no foods are off-limits as long as people consume them in “sensible portions” and do not exceed the recommended number of calories. The SlimFast website and app provide some sample recipes.

2. Two replacement shakes

Shakes are available in a shake mix or ready-to-drink format and come in various flavors, including strawberry, chocolate, vanilla, and cappuccino.

The SlimFast shakes contain 24 essential vitamins and minerals, along with 4–5 grams (g) of fiber and 10–20 g of protein, depending on the type of shake a person chooses.

3. Three snacks between meals

SlimFast offer a range of branded snacks, including bars and savory options. Alternatively, people can consume any 100-calorie snack of their choice.

While following the plan, individuals should drink plenty of water and exercise for 30 minutes each day. SlimFast state that men should add 200 calories to each meal replacement daily.

Once a person has achieved their desired weight loss, they can move to the SlimFast maintenance plan. This involves replacing one meal per day with a SlimFast shake or snack, eating two “sensible” meals of choice, and snacking between meals.

The SlimFast plan is available to view and purchase online.

According to SlimFast, their plan is compatible with a range of diets, including low carb, high protein, and vegetarian diets. There are not many options for vegans, however, as most meal replacements contain dairy or eggs.

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

The company also offer a keto range containing minimal carbs and a diabetes-friendly range for those who need to control their sugar levels.

Individual SlimFast products are available for purchase online.

Recipe ideas

The SlimFast website features sample recipes for breakfast, lunch, dinner, and snacks.

Some sample breakfast recipes include:

Some sample lunch and dinner recipes include:

Some sample 100-calorie snacks include:

When preparing the plan’s one daily meal, SlimFast recommend filling half the plate with vegetables, a quarter of the plate with lean protein, and a quarter of the plate with starch.

Although no foods are off-limits on this plan, eating certain foods ­— such as whole grains and lean proteins — can make it easier to stay within the calorie allowances. Some examples of foods in these categories include:

  • 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
  • nuts and seeds, and a person can choose any (in appropriate portions)

SlimFast allow alcohol in moderation. However, they suggest removing one daily snack if consuming a serving of alcohol.

Learn more about SlimFast meals and recipes here.

The SlimFast diet focuses on restricting calorie intake. When a person burns more calories than they consume, it will typically lead 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 study also notes that people who follow these diets tend to tolerate them well, and that they play a role in maintaining significant weight loss over 5 years.

SlimFast products are also high in protein, with the shakes containing 10–20 g of protein each, depending on the type of shake a person chooses.

Protein may play an important role in weight loss and feelings of fullness. One 2016 meta-analysis suggests that protein consumption can lead to increased feelings of fullness, which may cause people to have fewer cravings and eat less.

Studies on SlimFast

Research specifically focusing on the SlimFast plan indicates that it can promote weight loss. However, in some cases, it was no more effective than other weight loss aids.

A 2006 study that compared SlimFast with the Atkins diet, the Weight Watchers pure points program, and Rosemary Conley’s plan reports that people in all groups experienced significant and comparable body fat loss and weight loss over 6 months, compared with those in the control group. All participants had overweight or obesity at the beginning of the study.

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

According to one review of six randomized-controlled trials on SlimFast and similar meal replacement programs, which included a total of 487 participants, such plans can safely and effectively lead to significant and sustainable weight loss. It is important to note that several of the study authors were affiliated with the SlimFast company.

Some research also indicates that the SlimFast plan may effectively help adolescents with obesity lose weight in the short term, though the research found that it may not help them maintain that weight loss.

SlimFast may have some benefits and risks. The sections below will look at these in more detail.

Possible benefits

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

One 2001 study indicates that consuming meal replacement shakes, such as SlimFast, can be a safe and effective way for people with obesity and type 2 diabetes to lose weight and improve their glucose, insulin, and lipid levels.

Restricting calories, as well as making certain other lifestyle changes, may also improve heart health and prevent cardiovascular events in people who have overweight or obesity.

Some research also indicates that the SlimFast plan leads to cholesterol changes that may reduce the risk of cardiovascular disease.

Risks and disadvantages

One of the risks associated with meal replacement plans is the difficulty of maintaining the weight loss in the long term.

However, at least one study suggests that people find meal replacement plans easier to follow than other weight loss programs. This may help people adhere to the plan and achieve or maintain weight loss.

When people revert to their regular eating habits, they may regain some or all of the weight they lost. The absence of support from SlimFast, which may accompany other weight loss plans, may also contribute to this weight regain.

Also, for many people, the cost of the SlimFast shakes and snacks can be prohibitive, especially in the long term. Another issue to note is that this diet can become monotonous over time.

SlimFast focuses on calorie restriction without emphasizing the importance of consuming a variety of nutrient-rich foods. This does not teach people how to form healthful eating habits. Instead, the SlimFast plan relies primarily on heavily processed foods. One 2015 study indicates that people who eat a varied diet are less likely to have obesity.

There are several alternatives to SlimFast, including the following:

  • Medifast: This offers three weight loss plans and a range of meal replacement shakes, bars, soups, and other foods.
  • OPTIFAST: This includes a full meal replacement diet and a medically supervised plan.
  • Other meal replacement shakes: These are available in health stores and supermarkets.
  • DIY shakes: Individuals can make these at home using protein powders, yogurts, seeds, nuts, fruits, vegetables, and other ingredients.

When buying protein and meal replacement shakes, it is important to buy from a reputable brand. A 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 weight loss methods, such as restricting calorie intake or intermittent fasting, can also be effective.

Learn more about losing weight here.

The SlimFast plan can lead to significant weight loss for some individuals, at least in the short term. Some potential disadvantages of the diet include the lack of support and the difficulty of sustaining long-term results.

Additionally, it can be expensive to keep purchasing SlimFast products, especially when traditional weight loss methods — such as calorie restriction through counting calories or monitoring portion sizes — may be just as effective as using meal replacement shakes.

Another point to consider is that studies on SlimFast have typically involved participants with overweight or obesity. Therefore, it is difficult to know if people of a moderate weight would lose weight while following the SlimFast plan.