Protein Shake Fast: What Is It + 6 Reasons NOT To Do One

There are many different types of diets and weight loss tactics on the market, a protein shake fast being one of them, and as a nutrition coach I’m often asked about which strategies provide the best results.

So, is a protein shake fast worth it? Although a protein shake fast might result in weight loss, it is not a sustainable form of dieting since protein shakes are not a long-term replacement for whole foods. Not only will a prolonged protein shake fast leave you feeling hungry, but the weight loss you experience will likely only be temporary.

Although it can be tempting to jump into a new diet that promises great results, it is important to understand what exactly a protein shake fast is, along with the potential disadvantages of such a drastic diet.

Key Takeaways

  • A protein shake fast will not result in sustainable fat loss and any weight loss is likely to be regained
  • A protein shake fast is unnecessary because sustainable fat loss can be achieved simply by achieving a calorie deficit
  • There are more effective strategies that you can implement to achieve a calorie deficit and ensure long-lasting results

What Is a Protein Shake Fast?

A protein shake fast is a type of fast where you don’t consume any food other than protein shakes for a predetermined amount of time. 

Referring to this as fasting seems odd considering “fasting” typically means going without food or drinks with calories, but with a protein shake fast you are technically consuming calories, just not enough to adequately fuel yourself.

Some common protein shake fasting protocols are:

  • Replacing two meals per day with a protein shake. Having 2 meals per day from protein shakes with a third meal made up of whole foods. Common examples of this type of protocol are Isagenix and Herbalife.
  • Drinking only protein shakes for 24 hours. After 24 hours of only protein shakes you can expect to see decreases in water weight, but little to no decreases in fat.

For this article, I will be focusing on protein shake fasts where all you consume is protein shakes for 1 to 7 days.

Are There Any Benefits to Doing a Protein Shake Fast?

The main benefit that could be seen from doing a protein shake fast would be rapid weight loss. However, it is important to remember that this quick weight loss strategy is not sustainable, so it is likely that you will gain back any weight that you lost.

Considering that weight loss can be achieved without having to go on a liquid diet, there is no reason why a protein shake fast would be necessary.

A protein fast may be better than other types of fasting strategies (fasting without consuming any calories) because a protein fast would be more likely to help preserve muscle mass due to the high amount of protein you are consuming.

However, I still DO NOT recommend following a protein shake fast since there are other safe, effective, and healthy ways to lose weight without cutting out food and resorting to a liquid diet.

6 Reasons NOT To Do a Protein Shake Fast

6 Reasons NOT To Do a Protein Shake Fast
The reasons not to do a protein shake fast

In case I haven’t convinced you yet that a protein shake fast isn’t worth it, here are a few other reasons that you should NOT do a protein shake fast:

1. A Liquid Diet Isn’t Satiating Which Increases Hunger

Anytime that you replace a meal that consists of whole foods and fiber with a liquid meal, you are likely going to experience increased hunger and a decreased feeling of fullness after you eat.

While protein shakes do contain protein which normally contributes to feeling full, the protein found in shakes is digested much more quickly compared to the protein found in whole foods resulting in decreased satiety.

Additionally, when protein shakes are only mixed with water or milk, they lack fiber to help your stomach feel full and to slow down digestion. 

For this reason, a diet consisting only of liquids will cause you to be extremely hungry, making it hard to adhere to without exceptional willpower.

2. The Weight Loss You Experience Will Be Temporary

Protein fasts are not sustainable; therefore your results will not be sustainable. You will almost certainly regain the weight you lost, and perhaps more.

A 24-hour protein fast will likely cause the numbers on the scale to drop; however, this is likely related to a loss of water weight from a lack of carbs (1 gram of carb stores 3 to 4 grams of water) and not because you lost any fat.

Longer protein fasts (i.e. 1 week) would cause water loss and fat loss because after a week of only consuming protein shakes you would have created a significant calorie deficit which would result in fat loss.

However, any weight loss is likely to be regained because as soon as you return to your “normal” eating patterns, you will no longer be in a calorie deficit. 

You may even put on more weight than you started with because it can be hard to control yourself around food after you’ve been restricting food for so long.

Ultimately, protein fasts don’t encourage long-term success because this radical dieting method does not teach you about proper nutrition, how to lose weight sustainably, or how to change your habits to support your goals.

3. Only Drinking Protein Shakes Can Cause Digestive Issues

A significant and highly uncomfortable symptom of a protein shake fast is increased digestive issues, like increased gas, bloating, and constipation. 

While these are symptoms more commonly associated with whey protein, plant-based proteins can also be difficult to digest and cause similar issues.

Some individuals may experience digestive issues even with one protein shake per day, so having protein shakes all day long would only exacerbate these digestive issues.

Even those who don’t typically have digestive issues with protein shakes can develop issues with a protein shake fast because of a lack of fiber.

Fiber is essential for optimal digestive and gut health, and living off of protein shakes would drastically diminish your fiber intake. This lack of fiber can cause you to feel bloated and constipated until you return to a diet of whole foods.

4. Drastically Under-Eating Is Not Sustainable And Can Cause Negative Side Effects

While you are unlikely to experience any drastic side effects when following a protein shake fast for a brief period (i.e. 24 hours), remaining on this type of diet for longer periods (>48 hours) can cause more serious issues.

When you eat fewer calories than your body requires in a day, you will lose weight because your body will have to use its own resources (fat and sometimes muscle) for fuel.

A safe and healthy calorie deficit of around 250-500 calorie deficit (250-500 calories less than your maintenance calories) will help you achieve weight loss without losing muscle mass.

However, a protein shake fast will put you at a drastically larger deficit than is healthy and cause you to lose muscle mass. This loss in muscle mass will slow down your metabolism and cause you to burn fewer calories throughout the day.

For example, almost everyone requires more than 1200 calories per day even in a calorie deficit, so you would have to consume at least 10 protein shakes a day to be consuming enough calories to prevent muscle loss (assuming 130 calories per shake).

Even if you were able to consume enough calories from protein shakes for a healthier calorie deficit, the lack of nutrients would still likely cause extreme fatigue, nutrient deficiencies, and reduced immunity, making it more likely for you to get sick.

5. This Type Of “All-Or-Nothing” Diet Can Perpetuate An Unhealthy Relationship With Food

If you are someone who has a history of disordered eating, an unhealthy relationship with food, or an “all-or-nothing” perspective towards dieting, then a protein shake fast is going to make things worse, not better.

Consuming only protein shakes throughout the day in replace of food can perpetuate unhealthy dieting behaviors and cause you to be fearful of eating even the healthiest of foods for fear of weight gain.

Any type of diet that demonizes certain food groups and ruins your relationship with food to the point that you’re hyper-focused on what you’re allowed or not allowed to consume isn’t worth it.

6. Many Protein Powders Contain Processed Ingredients And Possible Impurities

One of the main issues that come with overconsuming protein shakes is that they are highly processed and therefore contain many processed ingredients that don’t provide any health benefits.

In fact, the majority of vitamins and minerals found in whey protein have been fortified and are not naturally occurring like those found in whole food protein sources such as meat.

It is also important to remember that protein powders are not a product that is regulated by the FDA, and upon further testing, some have been found to contain harmful ingredients and heavy metals that are bad for your health, especially in large quantities.

Lastly, most whey protein powders contain a plethora of processed ingredients such as artificial sweeteners which have been shown to have a variety of negative health effects.

While it is possible to shop for a higher quality protein powder with minimal additives that uses natural sweeteners, these protein powders still undergo extensive processing and do not compare to the nutritional value that whole food protein sources can provide.

One protein shake a day wouldn’t be an issue with a high-quality protein powder, but only consuming protein shakes for an extended period is another story.

Weight Loss Strategies That Are More Effective Than Protein Shake Fasts

If your goal is to lose weight, then the most effective way to achieve this goal is to determine a safe and healthy calorie deficit for your personal body type and activity level. 

For effective and sustainable weight loss, I recommend a calorie deficit of between 250-500 calories per day.

To determine how many calories 250-500 below your maintenance would be, you first need to find your maintenance calories (the number of calories that allows you to maintain your weight).

You can calculate your maintenance calories by finding your total daily energy expenditure (TDEE) using an online calculator

Once you have determined your maintenance calories, you simply subtract 250-500 calories from that number to determine an appropriate deficit for you.

For example, if my maintenance calories are 2200 calories per day then an appropriate calorie deficit would be 1700-1950 calories per day.

Here Are Six Different Ways That You Can Achieve a Calorie Deficit

Six different ways that you can achieve a calorie deficit

1. Calculating and Counting Your Calories and Macros

One of the most common ways to achieve a calorie deficit for fat loss is to count your calorie and macronutrient intake and track your daily food intake. 

This is arguably one of the best ways to reach your fat loss goal since the more accurate and consistent you are with your calorie deficit, the faster you will achieve your results.

Once you have determined your ideal calorie deficit (discussed above), you can then determine your ideal macronutrient percentages.

For fat loss, I would recommend eating around 30% of calories from protein, 40% from carbohydrates, and 30% from fat.

From there, the easiest way to track your daily food intake and hit your macronutrient targets is with the help of online or mobile food-tracking apps. 

These apps allow you to set your ideal calorie and macro targets and log your daily food intake to make sure you are hitting your goals.

My favorite calorie and macro counting apps to use that I would recommend are MacroFactor and Cronometer.

2. Focusing On Eating Whole Foods That Are High In Fiber

If tracking your calories isn’t for you, no worries at all! You can achieve a calorie deficit simply by focusing on eating whole foods.

Whole foods are higher in volume, loaded with fiber, and lower in calories so they help to fill you up faster and keep you full for longer.

This will make dieting much more tolerable and sustainable since constant hunger while dieting usually causes people to stray from their diet plan.

For an extensive list of the best high-fiber, low-calorie foods to include in your weight loss meal plan, check out this article.

3. Increasing Your Water Intake

Similar to eating plenty of fiber while in a calorie deficit, drinking plenty of water will not only keep you hydrated, but it will also help you to feel more full between meals which can help you achieve a calorie deficit.

 Swapping out any high-calorie beverages that you normally consume for water, which contains zero calories, is a great weight loss strategy that will contribute to your calorie deficit.

While the exact amount of water that you drink will depend on the individual, the typical recommendation is about 3.7 liters a day for men and about 2.7 liters a day for women.

4. Prioritizing Protein Without Neglecting Carbs And Fat

Another strategy for achieving a calorie deficit is to prioritize your protein intake (from whole foods) because protein is the most satiating macronutrient so it can help to keep you full for longer and minimize cravings.

Additionally, consuming enough protein is important for ensuring that you are preserving lean muscle mass while in a calorie deficit.

However, this does not mean that the other 2 macronutrients (carbohydrates and fat) should be neglected.

Having a source of protein, carbs, fat, and fruits or veggies at each meal will help to maintain essential body functions such as optimal energy, hormone production, and maintaining optimal nutrient levels in the body.

If you are someone who gets very hungry while trying to lose weight, then make sure you’re getting at least 30 grams of protein at every meal and at least one snack containing 10 to 20 grams of protein.

5. Increasing Your Physical Activity

You can also create a calorie deficit by increasing your activity level rather than decreasing your calorie intake.

A calorie deficit will result in fat loss whether it comes from reducing your calorie intake or increasing your calorie burn through exercise and movement. 

You could increase your physical activity simply by creating more opportunities to move your body throughout the day, such as taking the stairs every day instead of the elevator, or parking further away in a parking lot so that you have a farther distance to walk to the store.

My favorite way to do this is to set a step goal for the day so that I can quantify whether I’ve moved enough that day or if I need to get out and get some more movement in.

Another way to increase your physical activity is to deliberately increase the time and intensity of your workouts.

For example, if you normally do 10 minutes of cardio after a weight training session, you could increase this to 15 or 20 minutes for an extra calorie burn.

You could also try combining both an increase in physical activity and a decrease in calories in order to achieve your desired calorie deficit of around 250-500 calories.

6. Hiring A Nutrition Coach

One of the most effective weight loss strategies that you can implement is to hire a nutrition coach that can help you to develop a personalized plan to help you reach your goals. 

Unlike a generic protein shake fast, a nutrition coach is able to assess your current diet, mindset, activity levels, and the timeline for your goal and develop an effective plan based on that data.

A nutrition coach is also a great tool if you are someone who does better with more accountability and support with your diet. You can find out more information on working with one of our highly skilled nutrition coaches by clicking this link here.


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About The Author

Colby Roy

Colby Roy is a holistic health and nutrition coach. She is certified through Precision Nutrition and has a passion for all things nutrition and healing the body. More specifically, Colby likes to work with clients who want to optimize their gut health and energy levels.

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