The SlimFast Diet has been a popular weight loss tool for decades.
It consists of meal replacement shakes and food products designed to promote weight loss.
Its simple, convenient and easy-to-follow plan has garnered widespread success.
But many wonder if it really works, as well as if it’s sustainable.
This article takes a closer look at the pros and cons of the SlimFast Diet.
How we rated this diet. X
We considered six important standards and assigned a rating to each, with 1 being the lowest score and 5 being the highest. The Overall Rating for each diet is an average of these ratings.
Weight Loss or Weight Gain: This rating considers how fast the diet will make you lose or gain weight, whether the weight change can be sustained for 3 months or longer, and whether the diet is a crash diet. A crash diet is a very low-calorie, restrictive diet that comes with lots of health risks. Crash dieting can cause muscle loss, a slowed metabolism, nutritional deficiencies, dizziness, and more. They’re not safe or healthy.
Healthy Eating: This rating considers whether the diet limits entire food groups, and whether it disrupts your daily life with complex, specific requirements on what to eat or how to track your food. It also considers whether the diet focuses on long-term lifestyle changes and encourages habits like eating more whole foods, cooking at home, eating without distractions, etc.
Nutrition Quality: This rating considers whether the diet is based on whole foods rather than processed ones. It also considers whether the diet will cause nutrient deficiencies or a calorie deficiency if you do it for longer than 2 to 3 months. Though you can add vitamin and mineral supplements to any diet, it’s best to focus on getting what you need through a balanced diet.
Whole-Body Health: This rating considers whether the diet sets unrealistic goals, makes exaggerated claims, and promotes an unhealthy relationship with food or appearance. It also considers whether the diet promotes exercise and focuses on overall health rather than just weight. While you may have a weight-related goal you hope to achieve through dieting, it’s important to nourish your body and make sure you’re staying healthy regardless of how you choose to eat.
Sustainability: This rating considers how easy the diet is to follow, whether you can get support for it, and if it can be maintained for 6 to 12 months or longer. It also takes cost into consideration, since some diets require buying premade foods or paying membership fees. Diets that are sustainable are more likely to be healthy in the long term. Yo-yo dieting can contribute to health issues.
Scientifically Backed: This rating considers whether there’s evidence to support the diet’s health claims. We review scientific research to see whether a diet has been clinically proven by impartial research.
Overall score 2.58
Weight Loss 3.0
Whole Body Health 2.0
Healthy Eating 2.0
Nutrition Quality 2.2
The SlimFast Diet is a partial meal replacement plan that involves eating two meal replacements per day, in addition to three snacks.
You make one meal on your own, although there are guidelines for what foods to include and how many calories it should contain.
By replacing your regular meals and snacks with low-calorie, pre-prepared choices, you can reduce your daily calorie intake, resulting in weight loss.
On average, the SlimFast Diet provides approximately 1,200 calories per day for women and 1,600 calories per day for men.
The meal replacements are high in protein, which may help reduce your appetite and calorie intake (
The SlimFast Diet also claims to help keep your metabolism burning and ward off hunger.
It’s recommended to pair the diet with at least 30 minutes of exercise daily to help maintain weight loss.
Summary The SlimFast Diet is a partial meal replacement plan that works by reducing your calorie intake to promote weight loss.
If followed properly, the SlimFast Diet can be an effective way to lose weight.
It works by reducing your calorie intake to create a calorie deficit, which is when you expend more calories than you consume.
According to one review, following a low-calorie diet can lower body weight by an average of 8% in the short term (
SlimFast products are also high in protein, which can aid in weight loss as well.
One small study found that increasing protein intake by 15% reduced daily calorie intake by 441 calories and lowered body weight by 10.8 pounds (4.9 kg) over 14 weeks (
Many studies show that the SlimFast plan specifically may promote weight loss.
One study provided 63 people with meal replacements twice a day and instructed them to consume one low-calorie meal as well.
After six months, participants lost an average of 7% of their body weight and achieved a significant reduction in body mass index (
Another six-month study in 293 people evaluated the effectiveness of four popular diet plans, including SlimFast.
It found that those in the SlimFast group lost an average of 10.6 pounds (4.8 kg), while those in the control group gained 1.3 pounds (0.6 kg) (
Furthermore, one review of six studies analyzed the effects of meal replacement programs like SlimFast on long-term weight management. It concluded that meal replacement programs produced sustainable weight loss (
Summary SlimFast is high in protein and low in calories. Studies have found that SlimFast and similar meal replacement programs can produce significant and sustainable weight loss in the long term.
SlimFast is a popular choice because it’s easy to follow and flexible enough to fit into most lifestyles.
Unlike other diets, SlimFast provides the majority of your meals, making it harder to underestimate portion sizes or overeat.
In terms of health, losing even a small amount of extra body weight while following the SlimFast Diet can impart impressive benefits.
Research shows that following the SlimFast Diet or using other meal replacement programs may help support blood sugar control as well.
One study in 57 people found that liquid meal replacements like SlimFast not only increased weight loss but also improved blood sugar and insulin levels (
Another small, six-week study found that following a meal replacement regimen similar to SlimFast resulted in significantly decreased blood sugar levels (
Keeping your blood sugar under control not only reduces the risk of diabetes complications like nerve damage and kidney problems, it may also be associated with a lower risk of chronic conditions such as heart disease (
Summary Weight loss can improve multiple aspects of your health. SlimFast may also help improve your blood sugar and insulin levels.
The SlimFast Diet advises you consume two meal replacement shakes, cookies or bars per day in place of two regular meals.
You are also allowed up to three 100-calorie snacks per day.
Pre-portioned SlimFast products like crisps and chips are available, or you can use your own snacks instead.
Some 100-calorie snacks include:
- 1 medium banana
- 4 squares of chocolate
- 3 cups (24 grams) air-popped popcorn
- 1 slice of cheese
- 0.5 cup (143 grams) Greek yogurt
- 1 medium pear
You are also instructed to consume one sensible meal per day, which should be no more than 500 calories.
It’s recommended to make at least half of your plate vegetables, use one quarter for protein and fill the rest with starch.
Various meal recipes are provided, including:
- Chicken with quinoa and vegetables
- Eggplant lasagna
- Mandarin orange steak salad
- Egg muffin cups
- Cheeseburger with peppery coleslaw
You can consume this meal at any time of the day, as long as you’re also fitting in your two meal replacements.
Summary To follow the SlimFast Diet, consume two meal replacements and three 100-calorie snacks per day. You’re allowed one sensible meal daily, which should consist of mostly vegetables with some protein and starch.
No foods are off-limits on the SlimFast plan, as long as you stick within your daily calorie allotment.
For example, if you enjoy adding sugar to your morning coffee, it’s recommended to deduct those calories from your daily calorie limit, rather than cutting out the sugar altogether.
The diet even allows alcohol in moderation.
However, note that cutting back on alcohol can aid weight loss. SlimFast suggests removing a snack if you’re enjoying a glass of wine with your dinner.
That said, high-calorie foods will be very hard to fit into the SlimFast Diet.
You may include fast food, baked goods, sugary drinks and high-fat snacks, but the portion size will need to be severely limited to stay within your calorie goals.
Therefore, it’s best to stick to low-calorie alternatives, such as fruits, vegetables, whole grains and lean proteins, when preparing your snacks and meals.
Summary No foods are off-limits on the SlimFast Diet, but they must fit into your daily calorie goals. You can subtract extra calories consumed from your daily snacks or calorie allotment.
Below is a one-day sample menu to get you started.
- Breakfast: SlimFast Creamy Milk Chocolate Shake
- Snack: 1 ounce (28 grams) almonds
- Lunch: SlimFast Chocolatey Peanut Butter Pie Bar
- Snack: SlimFast Cinnamon Bun Swirl Drizzled Crisps
- Dinner: 3 ounces (85 grams) roasted salmon with one-half tbsp (7 grams) olive oil, 1 medium baked sweet potato with 1 tbsp (14 grams) butter, one-half cup chopped broccoli, roasted
- Snack: 1 cup (150 grams) baby carrots, 2 tbsp (30 grams) hummus
If you’re planning to start the SlimFast Diet, the first step is to stock up on the right products.
Here are some of the foods you should keep on hand:
- SlimFast meal replacements: Shakes, mixes, bars or cookies
- SlimFast pre-portioned snacks: Chips, crisps and snack bites
- Dairy or dairy alternatives: Skim milk, unsweetened nut milk or yogurt
- Lean proteins: Beef, chicken, turkey, salmon, tempeh, etc.
- Vegetables: Broccoli, asparagus, carrots, spinach, tomatoes, etc.
- Fruits: Apples, oranges, strawberries, blueberries, pears, etc.
- Whole grains: Quinoa, brown rice, barley, buckwheat, etc.
- Nuts and seeds: Almonds, walnuts, flaxseed, chia seeds
Research shows that SlimFast can be effective for weight loss, but it may not be the best long-term solution.
While meal replacement programs like SlimFast have been shown to be sustainable, going back to your regular eating habits can result in weight regain.
After achieving your weight loss goals, SlimFast recommends to continue replacing one meal per day with their meal replacement products, as well as sticking with the low-calorie snack options.
However, this can get costly, with shakes costing $1.50-4.00 for each serving.
The diet also puts the emphasis almost entirely on calories rather than nutrients, and it teaches you how to count calories rather than how to follow a healthy diet.
It may be an effective and easy short-term solution, but it should be paired with behavioral modifications and other healthy habits for long-term success.
Summary Following the SlimFast Diet in the long term can be costly, and going back to your regular diet after SlimFast can cause weight regain. The diet also focuses mostly on calorie counting rather than healthy eating.
The SlimFast Diet can be an effective weight loss method that works by replacing two of your meals per day with a meal replacement.
It’s high in protein and low in calories, and studies have shown it to be effective at promoting short-term weight loss.
However, there are some downsides to the diet. Also, it may not be the best option for long-term weight loss.
While the SlimFast Diet can definitely aid your weight loss efforts, it’s important to combine it with a healthy lifestyle and nutritious diet to maximize its effectiveness.