Top 23: SlimFast Diet

Author：Lisa Esposito Update：2024-11-06

The SlimFast diet is recommended for individuals who aim to lose approximately 20 pounds within a period of 8 to 10 weeks. The diet program, known as the 1-2-3 plan, involves consuming one nutritious meal, replacing two meals with SlimFast products, and having three snacks on a daily basis.

What Is the SlimFast Diet?

The SlimFast diet, which has been in existence since 1977, is well-known to many individuals. While it has evolved over time, it remains a meal replacement-based plan that incorporates shakes, smoothies, and meal bars as key components.

As part of the SlimFast diet plan, the three daily snacks may consist of SlimFast-branded snacks, fresh fruits, vegetables, or a small serving of nuts. The third meal of the day is considered a "sensible meal" and should contain approximately 500 to 600 calories.

SlimFast is particularly suitable for individuals aiming to lose around 20 pounds, a goal that can typically be achieved within eight to 10 weeks. Even after successfully losing weight, many individuals continue to incorporate SlimFast products as occasional meal replacements to facilitate weight maintenance.

Gluten-free friendly. Recipes can be easily modified and still follow a gluten-free diet.
Kosher friendly. Recipes can be easily modified and still follow the diet.

How Does the SlimFast Diet Work?

With SlimFast's 1-2-3 plan, you’ll eat one sensible meal, two meal replacements and three snacks daily.

There are five variations of the 1-2-3 plan:

Original. Becoming less popular than the other more specialized plans, the original SlimFast plan still relies on the products that have been on the market for over four decades.
Favorite Foods. Considered the most flexible plan, the Favorite Foods plan is based only on calorie tracking and allows for one SlimFast-approved meal each day. No food is off-limits, and you can choose any SlimFast products.
Keto. This variation is formulated for a high-fat, moderate-protein, low-carb ketogenic diet and features ingredients like collagen protein. These products are free of artificial sweeteners, colors and flavorings.
High Protein/Low Carb. While the keto plan focuses on eating high-fat foods, this plan is targeted to reduce carbohydrate intake, while allowing users to eat six times a day. You’ll eat a combination of Advanced Nutrition and Keto SlimFast products on the high protein/low carb plan.
Intermittent Fasting. SlimFast introduced its Intermittent Fasting plan in September 2022 with a line of products geared toward supporting time-restricted eating. During each person's eating period, the Intermittent Fasting meal bars, snack shake mixes and hydration supplements are designed to curb hunger and provide nutrients and energy.

Women consume approximately 1,200 to 1,300 calories per day on the SlimFast plan, while men are allotted an additional 400 calories daily, which can be consumed by doubling up on shakes or adding 200-calorie mini-meals throughout the day.

SlimFast Advanced Nutrition products are higher in protein and lower in sugar. They contain up to 20 grams of protein and as little as 1 gram of sugar. They are also gluten-free and high in fiber.

The Advanced Energy line is similar to the Advanced Nutrition line, but the shakes contain the same amount of caffeine found in a cup of coffee.

Can I Lose Weight on the SlimFast Diet?

Although SlimFast has been updated over the years to include education on healthy food preparation, intuitive eating and label reading, you are still relying on prepackaged foods for at least two meals and likely several snacks each day.

"When weight and blood pressure reduction are seen as an urgent clinical priority, some health care providers believe that getting the weight off quickly (by whatever means necessary) is the most important thing," explains Monica Reinagel, a licensed nutritionist, host of the Nutrition Diva podcast and co-founder of the Weighless program. "Some people find liquid meal replacements to work in that they lead to rapid weight loss, which can improve other clinical parameters."

Reinagel says she is always concerned about what happens next.

"Presumably, most don't envision subsisting on liquid meals for the rest of their lives," she explains. "There's a real danger that once they are out of the highly restrictive phase, the weight comes back on because those prior habits and behaviors haven't really been addressed. They've just been temporarily suspended."

Unless you want to continue doing a liquid diet for the rest of your life, you will need skills and education to keep the weight off and eat a nutritionally adequate diet.

"I think everyone underestimates the challenge of making the sort of permanent lifestyle changes required to sustain significant weight loss," Reinagel says. "This is why the intensive education and counseling is so critical. But if we're doing a good job with the education and counseling, the liquid meal replacements shouldn't be necessary."

Short-Term Weight Loss

In a 2009 study of more than 5,100 participants who were assigned to usual care or a meal replacement plan similar to SlimFast (the intensive lifestyle intervention group), participants who followed a meal replacement plan lost 8.6% of their initial weight, while the usual care group only lost 0.7% within the first year (1).
Other studies show that meal replacement diets are comparable in helping people lose weight to other low-calorie, low-fat diets; however, its convenience of prepackaged foods makes it easier for people to comply and adhere to the plan (2, 3, 4).

Long-Term Weight Loss

Programs that incorporate meal replacements “on some occasions during the day” have been shown to lead to more significant weight loss at one year, especially when paired with long-term behavioral change via counseling and education, according to a 2019 study (5).

Weight Maintenance and Management

Long-term results are encouraging.

In a prospective, randomized trial, participants who followed the SlimFast diet lost an average of 8.5% of their initial weight compared to 3.3% for the other group over the span of four years, demonstrating that liquid meal replacements can be a safe and effective strategy for patients with obesity (6).

Portrait of a beautiful woman drinking a green detox juice - healthy eating concepts

Close up of a young group of friends passing and serving food while enjoying together. They are having fun, chatting and feasting on food and drinks at dinner party

Do: Have two SlimFast meal replacements daily.

Shakes contain about 180 to 200 calories and meet 20% of your daily protein needs; they’re also packed with other essential nutrients, such as calcium, vitamin D and vitamin B12.

(Getty Images)

What Does the SlimFast Diet Cost?

Intermittent Fasting Sampler Bundle. $49.99.
Favorite Foods 14-Day Starter Kit. $79.99.
SlimFast Together Starter Kit. $169.99.
SlimFast Keto Quick Start Weight Loss 7-Day Starter Kit. $52.99.
Snacks, shakes and other items start at $9.99.

What Costs Are Related to the SlimFast Diet?

SlimFast products as detailed above.
The cost of food for your one prepared meal each day and any snacks you purchase and make yourself.

Doing SlimFast on a Budget

SlimFast product kits and bundles might save you money.
Finding SlimFast products at a warehouse club might cost less.
Preparing your snacks might be cheaper than purchasing the SlimFast branded options.

Is SlimFast Easy to Follow?

The SlimFast diet is ranked No. 24 in Easiest Diets to Follow (tie).

How easy it is to follow SlimFast depends on how long you want to dine on SlimFast shakes and snacks. There’s a wide variety of flavors, but if you don’t like the taste, the diet isn’t for you.

It's not recommended to replace all three meals per day with SlimFast products, as the plan encourages using natural foods to make the diet sustainable.

Eating out is allowed on SlimFast. SlimFast provides dining-out tips, such as ordering grilled or roasted entrees with steamed vegetables and requesting dressing and sauces on the side.

The SlimFast diet itself is a timesaver. Shakes and meal bars are all grab-and-go. You only need to think about preparing one meal a day.

Connect with fellow dieters and get support via the SlimFast Together Facebook community. SlimFast’s Brand Ambassadors, who’ve all lost weight and kept it off with SlimFast, respond to questions, as well, and the company interacts with dieters on its Facebook page. The SlimFast Together smartphone app helps you meet your goals on your personalized plan, for instance, with SlimFast Keto.

Nutrition experts emphasize the importance of satiety, the satisfied feeling that you’ve had enough. According to the company, the protein and fiber content of a SlimFast meal replacement can quell hunger for up to four hours.

However, the average SlimFast meal replacement only contains 180 calories, which is unlikely to keep you full for very long.

Who Should Not Try the SlimFast Diet?

Individuals with certain health conditions or who are on any medications should talk with their doctor before starting a diet or weight loss plan.

Products are designed around the nutritional needs of those 18 and older. If you’re younger, talk with a doctor before deciding whether SlimFast is advisable. Weight loss diets generally aren't appropriate for young people who are still growing.
Women who are pregnant or breastfeeding need more energy than is provided by the SlimFast plan.

Pros

Convenient – grab and go options.
A clearly defined plan with recipes.

Cons

Potential for monotony unless you customize.
Eating out is limited.
You’ll likely get hungry.
Unsafe for some people.

What Can I Eat? Do's and Don'ts of the SlimFast Diet

Foods to Eat

SlimFast meal replacement products – such as shakes, smoothies and bars – make up two of your meals for the day.
You’ll prepare one "sensible meal" for yourself within calorie limits. SlimFast recommends using the plate method to plan this meal: Fill half of your plate with vegetables, and then split the remaining half equally between lean protein and either whole grains or starchy vegetables.
Your three 100-calories snacks can be SlimFast-branded snack bars or foods you buy yourself.
With the Original and Favorite Foods plans, you keep an eye on calories. With the Keto and High Protein/Low Carb plans, you keep an eye on your macronutrient intake.

Foods to Avoid (or Limit)

SlimFast recommends eliminating alcohol, though having a drink once in a while is OK. Opt for a 6-ounce glass of wine (140 to 160 calories) rather than a margarita (possibly more than 500 calories).
Sugar-sweetened beverages, like juices and sodas, should be limited.
Portion control is a key component of SlimFast.

Vegan and Following the SlimFast Diet

Most SlimFast products contain dairy and are unsuitable for vegans. See all vegan diets.

Vegetarian and Following the SlimFast Diet

Lacto-vegetarians can proceed with the plan by following SlimFast’s suggestion of a 4- to 6-ounce serving of a meat alternative, such as quinoa or tofu, with their 500-calorie meal. See all vegetarian diets.

Gluten-Free and Following the SlimFast Diet

SlimFast contends its shakes are gluten-free, but other analysis notes it's still not a guarantee they don't contain gluten. Products other than shakes are not labeled as gluten-free, so read the ingredient list carefully. See all gluten-free diets.

Halal and Following the SlimFast Diet

No products are certified as halal, but they contain no animal products other than cow’s milk. See all halal diets.

Kosher and Following the SlimFast Diet

SlimFast Diabetic Weight Loss Shakes are kosher. See all kosher diets.

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