The SlimFast diet has been a popular weight loss program for decades, offering meal replacement shakes and food products designed to promote weight loss. While many people have found success with the plan due to its simplicity and convenience, it's important to consider whether SlimFast truly works and if it's a sustainable option. This article delves into the SlimFast diet, examining how it works, its potential benefits and drawbacks, and whether it's a worthwhile endeavor.
What is the SlimFast Diet?
The SlimFast diet, established in 1977, initially consisted of two low-calorie meal replacement shakes per day, accompanied by a "sensible" dinner. Over time, the company expanded its product line to include shakes, smoothies, bars, and snacks, offering Original, Advanced Nutrition, Advanced Energy, Diabetic Weight Loss, and Keto formulations.
The revamped SlimFast diet follows a 1-2-3 Plan, which includes 1 "sensible" meal, 2 meal replacements, and 3 snacks per day. Within this framework, you can choose from four versions: Original, Favorite Foods, Keto, and Low-Carb. While the company claims that you can lose weight in as little as 1 week, some skeptics question the diet's sustainability and affordability.
Who is SlimFast for?
SlimFast products are designed for individuals seeking a quick and convenient weight loss solution. Their low-calorie content and portability make them a suitable option for busy individuals. Moreover, SlimFast appeals to those who prefer a straightforward diet plan with minimal grocery shopping and food preparation. However, it's important to note that these products can be expensive and may not be accessible to everyone.
How the SlimFast Diet Works
The SlimFast diet is a partial meal replacement plan that involves consuming 1 "sensible" meal, 2 meal replacements, and 3 snacks per day, known as the "SlimFast 1-2-3 Plan" or the "SlimFast Plan."
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Four Versions of the SlimFast Plan:
- Original: Utilizes classic SlimFast products that have been available for over 40 years, though the company seems to be gradually phasing out this plan in favor of the Favorite Foods, Keto, and Low-Carb options.
- Favorite Foods: This plan doesn't have specific macronutrient goals and allows for one "SlimFast approved" meal per day, as long as you stay within your calorie limits. It is considered the company's most flexible and easy-to-follow plan.
- Keto: Designed for individuals following a keto diet, this plan emphasizes a high-fat intake by combining SlimFast keto products with one "sensible" keto meal. This plan can be challenging due to the strict macronutrient targets required to maintain ketosis.
- Low-Carb: Unlike the Keto Plan, the Low-Carb plan prioritizes reducing carbohydrate intake rather than consuming a high-fat diet. It also allows for three 100-calorie snacks per day from the SlimFast snack product line.
The underlying principle of the program is that by substituting regular meals and snacks with low-calorie alternatives, you can reduce your daily calorie intake, leading to weight loss. Additionally, some SlimFast meal replacement products are high in protein, which may help suppress appetite.
SlimFast claims that their diet keeps your metabolism burning due to frequent meals and snacks.
The SlimFast diet provides approximately 1,200-1,300 calories per day for women and 1,600-1,700 calories per day for men. The program also recommends incorporating at least 30 minutes of exercise per day to further promote the calorie deficit needed for weight loss.
Following the SlimFast diet is expected to result in a weight loss of 1-2 pounds (0.45-0.91 kg) per week.
SlimFast Together App
SlimFast offers the SlimFast Together app to help users stay on track and achieve their weight loss goals. The app includes a 5-minute quiz to identify your goals and preferences. You can then use the app for meal planning by selecting preapproved recipes or adding your own. The app also features a built-in calculator to help you monitor your calorie, macronutrient, and water intake.
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One of the most convenient features is the grocery ordering option, which 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.
The SlimFast Together app is currently available for free download on both Apple and Android devices.
Dietary Guidelines and Restrictions
While no foods are banned on the SlimFast diet, calorie restriction is essential. If you're following the Keto or Low-Carb plan, you'll also need to monitor your macronutrient intake.
Alcohol consumption is permitted, but the diet suggests keeping it to a minimum. To allow for flexibility, 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.
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Additional guidelines vary depending on the plan you choose. For example, the Keto plan requires a high-fat diet and the exclusive use of SlimFast keto products. Conversely, the Low-Carb plan focuses primarily on the carb count of your meals and allows you to use a combination of SlimFast Advanced Nutrition and keto products. The Favorite Foods plan offers the most flexibility, allowing you to select any of SlimFast's products and any "sensible" meal, regardless of macronutrient content, as long as it's SlimFast-approved.
Regardless of the plan you choose, you must also have two SlimFast shakes, smoothies, or bars as a replacement for two meals each day.
SlimFast shakes and smoothies are available as powdered mixes or in ready-to-drink bottles. Alternatively, you can opt for a meal bar. The bars come in a variety of flavors.
The meal replacement shakes and mixes provide roughly 180 calories and 14-20 grams of protein, though the amounts of carbohydrates, fiber, and added sugar depend on the product line. Likewise, the meal replacement bars provide around 180 calories and 7-15 grams of protein, depending on the product line.
The plan also encourages followers to have three snacks each day, consisting of SlimFast products or foods of your own choosing, as long as the snack has no more than 100 calories and fits into the macronutrient goals of your plan type.
Sample Meal Plans:
Here are examples of what a day of eating could look like on each plan:
- Favorite Foods:
- 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:
- 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:
- 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.
Cost of the SlimFast Diet
The cost of the SlimFast diet varies depending on the products you use, how often you use them, and whether you buy them in bulk.
Here are the current prices of popular SlimFast products:
- 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
The most affordable meal replacement options are the SlimFast shake mixes, costing $0.59-$0.72 per meal, depending on the size you buy. You can also purchase 14-day starter kits. The Favorite Foods and Low-Carb 14-Day kits cost $69.99, while the Keto 14-Day Starter Kit is more expensive at $89.99.
These kits include 2 meal replacements and 3 snacks per day, resulting in a daily cost of $5.00-$6.42 (excluding taxes), which translates to around $140 per month at minimum, not including the cost of your "sensible" meal.
You can potentially lower the cost by preparing some of your own snacks instead of purchasing the premade snack options.
Does SlimFast Promote Weight Loss?
The SlimFast diet can promote weight loss by reducing your calorie intake, creating a calorie deficit where you expend more calories than you consume. If followed correctly, the program restricts you to 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.
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. 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. 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. 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.
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. 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.
Though the SlimFast Together app provides some basic meal planning and progress tracking tools, it does not provide one-on-one counseling. It also relies heavily on SlimFast products instead of teaching sustainable habits such as learning to plan and prepare all meals and reading nutrition labels.
Therefore, it appears that using SlimFast products may help you lose weight in the short term, but there's a high chance that you'll regain weight once you discontinue the program.
Benefits of the SlimFast Diet
There are several benefits to the SlimFast diet:
- Easy to follow: 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.
- Products are accessible: SlimFast products are available at many supermarkets, grocery stores, and pharmacies around the United States.
- Costs less than other plans: Other diet plans like Jenny Craig, Nutrisystem, and Weight Watchers require you to commit to a long-term program to get a lower price. But SlimFast does not require a commitment.
- Provides built-in calorie counting: There is no need to download an app, keep a journal, or log foods.
- Encourages exercise: SlimFast is a proponent of exercise, although no formal program is provided. Some research has shown that exercise combined with meal replacement programs like SlimFast can lead to weight loss.
- May induce weight loss: The SlimFast diet restricts daily calories and will likely lead to short-term weight loss.
Downsides of the SlimFast Diet
While you may see some benefits to the SlimFast diet, there are many downsides to consider:
- 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 doesn't explicitly ban any foods, it restricts calories, which can feel restrictive for some people.
- Contains processed foods: The program is built primarily on processed foods. Most health experts recommend decreasing the amount of processed food you consume and increasing your intake of fresh or frozen fruits and vegetables, lean meats, seafood, and whole grains for optimal health.
- Limits healthy cooking: You may not learn healthy cooking methods on the SlimFast diet plan-and cooking is not required on the program.
- Disregards portion control: If you reach your goal weight on the SlimFast diet, you're going to have to eventually wean yourself off the program and maintain your weight loss.
- No long-term maintenance plan: Once you reach your goal weight, you are advised to slowly decrease your consumption of SlimFast and increase your intake of regular foods.
- Lacks good flavor: Not everyone likes the taste of SlimFast.
- High in added sugar: SlimFast shakes are high in sugar, including added sugar. If you ate a lot of sweets before the diet, you might be tempted to return to these foods.
Considerations for a Healthy Choice
Quick weight loss is likely on the SlimFast diet, and proponents claim you can stay on the program as long as you like. As with most meal replacement diets that restrict calories, regardless of how long you stay on them, you are likely to regain any weight once you resume normal eating patterns.
The USDA also advises limiting foods and beverages with higher amounts of added sugars, saturated fat, and sodium. While the SlimFast Diet does not restrict any foods, it restricts all of the recommended foods for two out of three daily meals.
As a meal-replacement diet, SlimFast does not meet the USDA's definition of a healthy meal plan since it replaces whole foods with shakes containing artificial ingredients and added sugars. Restricting daily calories to create a calorie deficit can certainly lead to weight loss in the short term, but restrictive diets, in general, are not sustainable eating plans.
A healthy diet that includes a variety of nutrient-dense whole foods combined with regular exercise can be one of the most effective weight loss strategies. Remember, following a long-term or short-term diet may not be necessary for you, and many diets out there don’t work, especially long-term. If your goal is weight loss, remember that losing weight isn’t necessarily the same as being your healthiest self, and there are many other ways to pursue health. Exercise, sleep, and other lifestyle factors also significantly affect your overall health.
Alternatives to SlimFast
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.
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.