The SlimFast diet, popular since the 1970s, traditionally involved replacing two meals with shakes and eating a sensible dinner. While effective for some in reducing calorie intake, the original shakes were high in sugar and unhealthy ingredients. Today, SlimFast has introduced a keto line, but are these products a safe and effective option for those following a ketogenic diet?
What is SlimFast?
SlimFast is a company that sells weight loss and nutrition products. It was first launched in 1977 but didn’t become popular in the United States until the 1990s. When the company first came out, they only sold weight loss shakes. These shakes came in a can, and their signature red and white label could be spotted from a mile away. It wasn’t until 2009 that the company started selling low-carb products.
The Original SlimFast Diet: A High-Sugar Approach
The original SlimFast diet had you drinking a shake for breakfast and lunch, and then eating a low-calorie meal for dinner. Many people lost weight on the SlimFast diet simply because they reduced their calories, but then gained it all back (and then some) when they started eating real food again. The ironic thing about the SlimFast diet was that its popularity spread like wildfire.
The problem with the original SlimFast shakes is that they were full of sugar and canola oil, which is the opposite of what we now know to be healthy.
Original SlimFast ingredients included:
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- Fat-free milk
- Water
- Sugar
- Canola oil
- Maltodextrin
- Milk protein concentrate
- Cellulose gel
- Cellulose gum
- Natural and artificial flavors
- Mono and diglycerides
- Potassium phosphate
- Soy lecithin
- Calcium phosphate
- Carrageenan
- Sucralose
- Acesulfame potassium
The use of sugar, skim milk, acesulfame potassium, sucralose, canola oil and maltodextrin makes this a very low-quality and highly processed product.
SlimFast's Keto Offerings: A New Approach
Luckily, SlimFast heard about the keto diet and decided to launch its own line of products. They now offer bars, shakes, and even fat bombs with fewer carbs than their original products. SlimFast also offers a line of so-called diabetic weight loss products, including meal bars, shake mixes, and snacks.
Here's a look at some of the SlimFast keto products available:
- Fudge Brownie Batter Shake Mix: Ideal for chocolate lovers, this mix can be combined with 8 ounces of water.
- Vanilla Cake Batter Shake Mix: A non-chocolate alternative with low-carb ingredients, vitamins, and minerals. Simply add 8 ounces of water.
- Peanut Butter Cup Fat Bombs: Designed as a sugar-free dessert option.
- Peanut Butter Chocolate Bar: SlimFast claims that this peanut butter chocolate bar is fluffy, filling and perfectly full of peanuts.
- Keto Meal Bar: This keto meal bar contains whey protein and MCTs from coconut oil.
- MCT Oil: SlimFast’s MCT oil contains non-GMO MCT oil from 100% pure coconut oil with C8 Caprylic acid. It can be added to recipes, coffee, and baked goods.
- Urine Ketone Test Strips: For monitoring ketone output.
- Ready-Made Keto Shakes: Convenient, grab-and-go shakes.
- Ultra Hydration+: An electrolyte powder sweetened with stevia to aid hydration during ketosis.
- Fat Bomb Shot: A tangy orange creme flavored shot.
SlimFast Keto Shake Mix is back! Shake up your daily keto routine and indulge in cheat-day flavors every day with a good source of protein, 15g fat, 4-5g net carbs and 0g added sugar* per serving. Perfect for a quick and easy meal replacement that tastes like your favorite desserts, you’ll always have a way to get the keto-friendly nutrients you want without having to look up the numbers. All you need is a serving of SlimFast Keto Shake Mix, water, and a shaker cup or blender to stay in your keto groove! Keto-Friendly Meal Replacement Shake: good source of protein, 15g fat, 4-5g net carbs and 0g added sugar* per serving. Can Be Part of the SlimFast Plan: Clinically proven to help you lose weight and keep it off - one sensible meal, two meal replacement shakes, and three 100 calorie snacks each day. Indulgent Cheat-Day Flavors: Vanilla Cake Batter & Fudge Brownie Batter Keto-Friendly: Made with whey protein, collagen peptides, butter & MCT oil. Keto Made Easy: All you need is a serving of SlimFast Keto Shake Mix, water, and a shaker cup.
The SlimFast Plan: How it Works
The SlimFast diet is a partial meal replacement plan that involves eating 1 “sensible” meal, 2 meal replacements, and 3 snacks per day. This is known as the “SlimFast 1-2-3 Plan” or the “SlimFast Plan.”
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You can choose to follow one of four versions of this plan:
- Original. This plan uses popular SlimFast products that have been around for more than 40 years. However, it appears that the company is slowly phasing out this plan in favor of the Favorite Foods, Keto, and Low-Carb plans.
- Favorite foods. This plan does not have specific macronutrient goals and allows for one “SlimFast approved” meal per day as long as you stay within your calorie limits. This is considered the company’s most flexible and easy-to-follow plan.
- Keto. Designed for people following a keto diet, this plan focuses on a high fat diet by combining SlimFast keto products and one “sensible” keto meal. This plan is the hardest to follow because of the strict macronutrient targets needed to maintain ketosis.
- Low-Carb. Unlike the Keto Plan, the Low-Carb plan focuses less on consuming a high fat diet and more on eating fewer carbohydrates. You’re also allowed three 100-calorie snacks per day from the SlimFast snack product line.
The idea behind the program is that by replacing your regular meals and snacks with low calorie choices, you can reduce your daily calorie intake, which should result in weight loss. Additionally, some SlimFast meal replacement products are high in protein, which may help reduce your appetite (2).The SlimFast diet also claims to keep your metabolism burning because you consume frequent meals and snacks.
According to SlimFast, the SlimFast diet provides approximately 1,200-1,300 calories per day for women and 1,600-1,700 calories per day for men (3).Additionally, the program recommends pairing the diet with at least 30 minutes of exercise per day to further promote a calorie deficit needed for weight loss.By following the SlimFast diet, you’re expected to lose 1-2 pounds (0.45-0.91 kg) per week (3).
A Sample Meal Plan
Below are examples of what a day of eating could look like on each plan.
Favorite Foods sample meal plan
- Breakfast: SlimFast Meal Shake
- Snack: banana
- Lunch: SlimFast Meal Bar
- Snack: 3 cups (24 grams) air-popped popcorn
- Dinner: Chicken Tikka Masala
- Snack: SlimFast Double Chocolate Mint Crunch Mini Snack Bar
Low Carb sample meal plan
- Breakfast: grilled veggie omelet
- Snack: 1/2 cup (143 grams) Greek yogurt
- Lunch: SlimFast Meal Shake
- Snack: 1 slice of cheese
- Dinner: SlimFast Diabetic Weight Loss Meal Bar
- Snack: SlimFast Diabetic Weight Loss Snacks
Keto sample meal plan
- Breakfast: SlimFast Keto Meal Shake
- Snack: SlimFast Keto Fat Bomb Real Cheddar Cheese Crisp
- Lunch: SlimFast Keto Fat Bomb Meal Bar
- Snack: baked zucchini fritters
- Dinner: baked salmon with lemon butter and steamed asparagus
- Snack: SlimFast Keto Fat Bomb Dark Chocolate Almond Snack Square
For men, the program recommends adding 200 calories to each SlimFast meal replacement or doubling your meal replacements.
Read also: Easy Low-Carb Cheese Crackers
Cost of SlimFast
The cost of the SlimFast diet depends on which products you use, how often you use them, and whether you buy them in bulk.
Here are the current prices of popular SlimFast products (4, 5, 6):
- Ready-to-drink meal replacement shakes: $9.99 for a pack of 4 shakes or $91.96 for a 4-pack of 12 shakes (48 bottles total)
- Meal replacement bars (excluding the Keto Bomb Bars): $9.99 for a pack of 5 bars or $39.96 for a 4-pack of 5 bars (20 bars total)
- SlimFast shake mixes: $9.99 for a 14-serving (12.83-ounce) container or $12.99 for a 22-serving (20.18-ounce) container
Overall, the cheapest meal replacement options are the SlimFast shake mixes, which cost $0.59-$0.72 per meal, depending on the size you buy (6). You can also purchase 14-day starter kits. The Favorite Foods and Low-Carb 14-Day kits cost $69.99, and the Keto 14-Day Starter Kit is more expensive at $89.99 (7).
These kits include 2 meal replacements and 3 snacks per day and would have a daily cost of $5.00-$6.42 (excluding taxes) (7). For a month, this equals around $140 at minimum. Keep in mind that this doesn’t include the cost of your “sensible” meal (7).
You can potentially lower the cost by preparing some of your own snacks instead of purchasing the premade snack options.
Can SlimFast Help You Lose Weight?
The SlimFast diet can promote weight loss by reducing your calorie intake to create a calorie deficit, meaning that you expend more calories than you consume. If following the program correctly, you would consume only around 1,200 calories per day. Some older studies on SlimFast products suggest they may support meaningful weight loss. However, most studies on SlimFast are older, which may be due to the growing trend toward programs that promote sustainable weight loss (9, 10, 11).
For example, a 2006 study evaluated the effectiveness of 4 popular diet plans, including SlimFast, over the course of 6 months in 293 people with a BMI between 27 and 40 (12). The study found that those in the SlimFast group had lost an average of 10.5 pounds (4.8 kg), or 4.9% of their body weight, after 6 months (12). However, 29% of participants dropped out of the study because they couldn’t tolerate the diet, and only 9 of the original 58 participants were able to maintain the diet for 12 months at follow-up.
Further, two reviews of meal replacement companies and popular weight loss programs found that SlimFast may support short-term weight loss but is not significantly more effective for weight loss than competitor programs (13, 14). More recently, a 2019 review found that meal replacement products may be effective for achieving a calorie deficit but should be paired with other behavioral strategies, such as counseling, developing food skills, and enhancing self-efficacy (15).
Similarly, a 2018 study compared the effects of behavioral therapy, behavioral therapy combined with SlimFast meal replacements, and a comprehensive nutrition intervention that focused on both internal and environmental influences on food choice (16). By the end of the study, the comprehensive nutrition intervention had led to the most weight loss. The authors suggested this was due to greater cognitive restraint, self-control skills, and self-efficacy, which are important factors for sustainable weight loss (16).
SlimFast Together app
SlimFast Together is a relatively new app the company offers to help you stay on track and achieve your weight loss goals. When you first open the app, you’ll complete a 5-minute quiz to identify your goals and preferences. You’ll then be able to use the app for meal planning by selecting preapproved recipes or adding your own. The app also has a built-in calculator to help you know whether you’re meeting your calorie, macronutrient, and water goals for the day.
Perhaps the most convenient aspect is the grocery ordering feature that automatically creates a shopping list from prepared menu items and allows you to place a grocery delivery or pickup order from a local retailer.
The app also includes a progress tracking feature that allows you to enter information about your current weight, measurements, diet, water intake, exercise, sleep, and stress. You can even add progress photos.
SlimFast Together is currently free to download on both Apple and Android devices. SlimFast offers four plans: Original, Favorite Foods, Low-Carb, and Keto.
To sign up for the Favorite Foods, Low-Carb, or Keto plan, you’ll be required to first download the SlimFast Together app. If you’re unsure which plan to choose, you can complete a quick quiz on the app, which will provide a personal plan recommendation based on your goals, preferences, and lifestyle.
Once you’ve selected a plan, you can choose a pre-designed meal plan or create a customized meal plan for the week. The app will then curate a shopping list, which you can take with you to the store or use to order groceries online. With this plan, you’ll receive a quick-start guide and a 7-day meal planner to help you stay on track.
Pros and Cons of SlimFast
Pros:
- Easy to follow: Unlike many other diets, SlimFast provides the majority of your meals, and the meals require little or no preparation, making the plan easy to follow. Furthermore, as SlimFast meal replacements are pre-portioned, you don’t have to worry as much about figuring out portion sizes or overeating. The program also provides easy-to-follow recipes, and the SlimFast app helps you stay organized.
- Convenience: Instead of having to prepare multiple meals a day, you need to prepare only one. To make things even easier, SlimFast offers simple preapproved recipes that can help you stay on track. Additionally, SlimFast products are convenient for people who are on the go and don’t have time to prepare a meal.
- Promotes other healthy habits: The new SlimFast Together app includes useful tools to track your healthy lifestyle habits, such as sleep, stress, food and water intake, and physical activity. Though SlimFast doesn’t provide personalized recommendations, this new addition can help users focus on a well-rounded healthy lifestyle.
Cons:
- One-size-fits-all approach: A major downside to the SlimFast diet is its one-size-fits-all approach. The diet assumes that everyone requires the same number of calories per day, without taking into consideration your height, weight, activity level, age, and other factors that can affect how many calories and nutrients you need in a day. All four available plans focus on a calorie goal of 1,200-1,300 calories per day for women and 1,600-1,700 calories per day for men.
- Highly processed foods: The healthiest diets consist of mostly whole, minimally processed foods high in fiber, protein, healthy fats, and beneficial plant compounds such as antioxidants. However, most SlimFast products are highly processed, containing a long list of added ingredients such as added sugars, protein powders, and artificial sweeteners, colors, and flavors.
- Lack of variety for different dietary needs: The majority of SlimFast products use milk as the main ingredient, and there are no alternative options for people who follow a plant-based diet or wish to avoid dairy. If you have food allergies, you’ll want to pay close attention to each ingredient list. Also keep in mind that, because they may have been manufactured in facilities that handle common allergens, packaged SlimFast products likely aren’t safe if you have a severe food allergy or intolerance.
- Can feel restrictive: Though the diet permits one “sensible” meal per day, which can include any foods of your choosing from a list of “SlimFast approved” meals. These will vary depending on which plan you’re following.
Concerns with SlimFast Keto Products
Despite SlimFast's attempt to cater to the keto community, their products may not be ideal for strict ketogenic dieters.
- Questionable Ingredients: Some products contain ingredients that aren't strictly keto-friendly, such as tapioca syrup, soy, carrageenan, milk, and dextrose/maltodextrin (derived from corn). Typically, these ingredients are avoided by most strict-keto dieters.
- Higher Net Carb Count: SlimFast snacks and shakes have a MCT blend that includes palm in many of their products, and their net carbs tend to linger around 4 carbs or more.
- Preservatives: Many SlimFast products contain a great deal of preservatives.
- Blood Sugar Spikes: Some online reviewers even state that their blood sugar levels jump after consuming SlimFast products.
Customer Reviews and Concerns
Customer reviews provide mixed feedback on SlimFast products. Some users report success with weight loss and enjoy the convenience of the shakes. However, others express concerns about the taste and texture of the new meal replacement bars, changes in packaging, and the use of artificial ingredients.
Some specific complaints include:
- Changes in Meal Replacement Bars: Some reviewers note a strange texture and unpleasant, synthetic taste in the new meal replacement bars.
- Packaging Issues: Concerns have been raised about the increased use of plastic in packaging.
- Taste and Quality: Some customers have reported a bad taste or rancid quality in the ready-made shakes.
- Customer Service: Negative experiences with customer service have been reported.
Better Keto Alternatives
If you’re trying to adopt a healthy ketogenic lifestyle, then it’s more important to focus on healthy keto-friendly foods. SlimFast’s keto products claim to have low net carbs, thanks to their high fiber content. Both fiber sources are popular among cheaper, lower-quality products aimed at people who are watching their carb intake.
If you want to lose weight on a ketogenic diet, there are many things you need to know. Instead, just eat real food and healthy fats from foods like MCT oil, grass-fed butter, nuts, and seeds, avocados, and more.