Drinking Only SlimFast For A Week (Will I Lose Weight?)

Share this article:

Yes, you can lose weight by drinking only SlimFast meal shakes or smoothies for a week if you follow its 1-2-3 diet plan and limit your daily caloric intake to 1,200 (for women) or 1,600 (for men). You should not replace all your daily meals with only SlimFast products. These are very low in calories, contain many added sugars, and are filled with fortified vitamins and minerals, which can put you at risk of chronic diseases. 

I can’t count how many weight loss programs and diet plans are available in the industry today. Bet, you couldn’t too, yeah? 

They all promise the crowd one thing: effective weight loss in like as fast as a week or two. Yep, that’s possible! But only if you do it with SlimFast.

Of course, that statement would make you think like “How is SlimFast more effective than others?” Well, let’s learn more about this diet below.

What is SlimFast?

SlimFast promises you can lose up to 1-2 lbs (0.45-0.91 kgs) per week through its 1-2-3 diet plan. 

The SlimFast diet requires you to eat one “sensible” daily meal containing not more than 600 calories for women, and 800 calories for men, replace two meals with protein SlimFast meal replacement shakes or bars, and eat 3-100 calorie snacks in between (SlimFast snack bars, fruits, veggies, or nuts).

Following the plan with a low-intensity exercise like simply walking for at least 30 minutes a day will guarantee you reach your target weight. 

How does the SlimFast diet plan work?

The SlimFast diet plan lets you on a calorie deficit which means that you will be consuming lesser calories than you burn.

This will cause your body to burn your stored fats into energy resulting in weight loss. 

Generally, the program allows women to only consume 1,200 calories and men only up to 1,600 calories per day. 

However, you shouldn’t restrict yourself to as low as 1,000 calories per day unless your doctor tells you to. 

While a very low-calorie diet (VLCD) is effective for weight loss, it is not recommended and safe for everybody. 

When you’re on VLCD, you wouldn’t be giving your body enough nutrients, resulting in poor cognitive and bodily functions and a slower metabolism.

It may also result in minor side effects like fatigue, constipation, nausea, and diarrhea.

A young woman on a low calorie diet is feeling fatigue while working out because she doesn't have as much energy

In very worst cases, you could also develop gallstones.

You shouldn’t replace your three daily meals with SlimFast replacement shakes and bars. These products are very low in calories, causing you to starve all day. 

Drinking only SlimFast shakes to meet your daily required calorie intake could also cause serious health issues.

These diet shakes are highly processed and contain fortified vitamins and minerals, which could have more added sugar and artificial ingredients and cause vitamin overdose. 

How long can you see results on SlimFast?

Losing weight is unique to everybody. 

You can stay on the SlimFast diet plan for as long as you like or until you reach your weight goals. 

The SlimFast company claims that you can achieve weight loss in just one week following their diet program. 

With their new product lines, you can have many options on what diet products to add to your grocery list. 

These include gluten-free and fiber-rich protein meal bars, premade protein meal shakes with caffeine, smoothies, and powdered protein shake mixes in various flavors. 

SlimFast also features recommended products for people with a ketogenic lifestyle and Type 2 diabetes. 

How to start the SlimFast diet?

It’s very easy to get started with SlimFast as the company has laid out everything for you. 

You can start by signing up for what plan you want to follow on their SlimFast Together App

A young woman is using her mobile diet app to stay on track with her temporary low-calorie diet.

First, download the app and choose between the Favorite Foods, Low Carb, and Keto plans.

If you don’t know what to choose yet, the app allows you on a quiz and will recommend what plan suits you best based on your goals, preferences, and lifestyle. 

You can still jumpstart your weight loss goals without downloading the app by signing up for the SlimFast Original plan on the company’s website.

SlimFast will send you a 7-day meal plan to keep you on track for a week, no matter what plan you choose. 

What’s more exciting is the app allows you to choose different recipes for your homemade meals and calculates your calorie, macronutrient, and water intake for the day. 

It also personalizes a grocery list based on your recipes and keeps track of your progress. 

What can you eat on the SlimFast diet?

No wonder why many people follow the SlimFast diet to lose weight because they can still eat their favorite food for one single meal every day. 

However, you should watch your caloric intake closely without the food restriction and not go over your daily caloric allotment.

This means you have to reduce your portion sizes when eating your favorite foods, including your alcohol and coffee intake. 

SlimFast recommends you only drink alcoholic beverages once in a while.

Try to opt for a 6-ounce glass of wine (lower than 200 calories) rather than a margarita (over 500 calories), or take a shot of hard liquor with a calorie-free beverage (about 70 calories). 

You should also limit sweetened fruit juices, sugary drinks, and sodas. 

Is caffeine okay with SlimFast diet?

An older man is drinking black coffee while on his low-calorie diet

Drinking coffee and tea is okay as they contain very few calories. But if you add sugars and milk to your drink, you may have to skip one or two of your snacks.

To put it simply, you must reconstruct your meal plan and fit it into your daily caloric allotment.

In addition, stay away from buying milky coffees in coffee shops as they may contain many calories.

It’s okay to do so but be sure that you don’t go over your allotted daily caloric intake.

How to lose weight with SlimFast in two weeks?

SlimFast diet plan is very easy to follow.

If you want to lose weight within two weeks, you have to sign up on SlimFast Together App and choose a diet plan.

Whether you choose the Favorite Foods or Keto plan, you must follow the 1-2-3 diet plan to achieve weight loss.

The general guidelines for the SlimFast diet plan include the following:

  1. Replace your two daily meals with a SlimFast protein shake or meal bar.
  2. Eat 500 (for women) to 800 (for men) calories on your third meal. The SlimFast Together App or website will suggest recipes or create a meal plan based on your chosen diet plan (Favorite Foods, Low Carb, and Keto plan)
  3. Enjoy 3- 100 calorie snacks each day. It could be a SlimFast bar, steamed veggies, frozen fruits, or nuts.
  4. Eat no more than 1,200 calories (for women) and 1,600 calories (for men) per day.
  5. Do light to medium exercise for 30 minutes each day. Avoid high-intensity workouts, which may cause you to feel exhausted and hungry afterward.
  6. Drink plenty of water. It also helps in suppressing hunger and cravings.

Pros and Cons of SlimFast diet

While you may see many success stories of people on the SlimFast diet program, it’s not hard to ignore that many people have dropped out and did not sustain their weight loss for a long time.

Yes, SlimFast is a very effective weight loss regime, but it isn’t an ideal diet plan for the long term.

Why? Below you can read more about the pros and cons of the SlimFast diet program.


1. Easy to follow

The SlimFast diet plan requires little to no preparation.

Premade recipes for you to cook and various meal replacement shakes or bars are available, making it easy to follow. 

It only requires you to follow the 1-2-3 diet plan, and you’re on your way to achieving your weight goals.

SlimFast products are already portion-controlled, so you don’t have to worry about calories and overeating

In addition, there’s no restriction on what you want to eat on your “sensible” meal, whether it’s homemade or a take-out.

You just have to make sure you don’t go over your daily allotted caloric intake. 

2. Convenient and accessible products

If you’re an always on the go type of person, the SlimFast diet suits you best. 

You only have to prepare one meal every day, perfect for people like you! 

The SlimFast Together App provides premade, easy-to-follow recipes, allowing you to add your own and create a grocery list based on your recipes. 

The app already has a built-in calorie, macronutrient, and water intake calculator.

SlimFast products are available in supermarkets, grocery stores, and pharmacies all over the United States.

You can also buy these products online and have them delivered to your doorstep. Just pay the shipping fee!

3. Costs lower than other diet programs

Some diet plans may require you to sign up for a long-term commitment with their programs to get discounts. 

But, with SlimFast, nothing holds you back if you only want to lose weight quickly within a week or a month.

You don’t need to pay and cancel any meal services or subscription plans.

4. Keeps you on track and promotes better lifestyle habits

With the SlimFast Together App, you will be encouraged to promote healthy lifestyle habits by tracking your daily sleep, stress, food, water intake, and physical activity.

This can help you focus on your daily goals and track your progress. 

5. Effective weight loss

SlimFast has been clinically proven to induce weight loss for many decades now. 

A couple are running together outside to stay on track with their weight loss goals

Researchers suggest that SlimFast could help you lose weight and reduce your risk of developing type 2 diabetes.

Obese and overweight people with type 2 diabetes may improve their glucose, insulin, and lipid levels by following the SlimFast diet plan.


1. Highly-processed replacement shakes and bars

Most SlimFast products are very processed, containing high amounts of added sugars and artificial ingredients.

These are not recommended by health experts to consume for a long time because these could trigger or put you at risk of chronic disease.

2. No personalized plan or support

SlimFast doesn’t calculate how many calories and nutrients you need in a day based on your height, weight, activity level, age, and other factors.

It assumes that everyone requires the same daily caloric intake. 

3. Doesn’t promote healthy eating habits

Since the diet plan only requires you to eat one hearty meal every day, you might disregard choosing healthy options and just eat out or buy ready-to-eat processed food. 

Moreover, the program doesn’t teach you to develop habits like home cooking, mindful eating, and reading nutrition labels.

Once you achieve your weight goals, it’ll be hard to maintain your weight without regaining any.

4. Restrictive and very low-calorie diet

Although, SlimFast wants you to be flexible with your diet eating whatever you want in one meal per day, watching calories could feel very restrictive.

Moreover, most replacement shakes and bars are very low in calories which could not provide you sufficient nutrients, leaving you feeling hungry throughout the day.


Why am I gaining weight on SlimFast?

There could be many reasons why this could happen to you. One thing for sure is that losing weight is unique to everybody.

Maybe your body is adjusting to the weight loss plan. Give it more than two weeks and see if the numbers on your scale will drop.

When you’re on the SlimFast diet, make sure that you follow the guidelines of the 1-2-3 (or 3-2-1, whatever it is) diet plan. Don’t go over the allotted daily caloric intake; 1,200 for women and 1,600 for men.

Also, balance cardio and strength training on your diet to make sure you’re not just burning fat but also building muscles.

The bad news is that SlimFast products are highly processed.

They contain many added sugars and are produced from non-organic ingredients, contributing to weight gain.


When your body burns more calories than you take, it’ll help you lose weight. This is how the SlimFast diet works. It lets you on a calorie deficit by following its 1-2-3 diet plan.

You can replace your meals and snacks with SlimFast milkshakes and bars that are basically low-in calories.

While SlimFast guarantees you can lose up to 1-2 lbs (0.45-0.91 kgs) per week, it has many downsides.

Researchers suggest that this diet doesn’t help you build sustainable long-term habits.

When you wean off with this program, you’ll have difficulty maintaining your weight and eventually gain it all back.

So, it’s safe to say that you shouldn’t do something on your diet that you can’t stick to for a long-time.

Perhaps, you should try to slowly cut out the added sugars, oily or fried, and fatty food and drinks in your diet.

Instead, switch to organic, whole-foods and cook homemade meals, which can help you build healthier habits in the long run. 

Share this article:

Was this article helpful?
Reana Jean Cuevas
Mabuhay! I'm Reana Jean Cuevas. A healthy body means living well with no worries-just happiness and more life adventures. Taking care of my body and well-being is an investment for my career and future. I was a volunteer at the Philippine Red Cross. I joined the training to become a first-aider and be able to provide other health and safety services in my community. I love discussing anything but mainly first-aid, home remedies, and women's health.

We’re proud to be a team of writers who are truly passionate about all things health.

Coming together from all parts of the world, we share a common goal of helping serve many with our comprehensive research and clear writing style. Learn more.

Nutrition & Diet