Fasting and Protein Shakes: Can You Drink A Protein Shake While Fasting

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Written By Nicolette
Nicolette has been a certified dietician and nutritionist for over ten years, whose work has been featured in the likes of Reader’s Digest, Eat This, Not That, Everyday Health, and Shape. She believes in emphasizing a holistic approach toward food and nutrition.

Fasting and protein shakes – but can you drink a protein shake while fasting, let’s explore the science, the pros and cons as well as some helpful considerations.

Can You Drink Protein Shakes While Fasting?

Although protein shakes can contain amino acids that cause insulin levels to spike and break a fast, consuming them during the restricted fasting window may be acceptable if done carefully, with the right timing and types of shakes. However, protein shakes do contain calories and may be considered breaking your fast.

The Effect Of Protein Shakes On Insulin Levels

For those looking to lose weight, or those simply wanting to maintain general health protein shakes are a popular option.

But how do they affect the body when consumed while fasting?

First, it’s essential to understand that certain types of protein can raise insulin levels in the body, meaning that consuming a protein shake during fasting could potentially break the fast. (1)

For instance, whey proteins have been found to increase insulin secretion more so than other types of proteins. (2)

On the other hand, casein proteins take longer to digest and absorb which can help keep glucose levels stable for longer periods and reduce overall spikes in blood sugar throughout the day. (3)

While plant-based proteins like soy or pea don’t contain as much leucine (an amino acid responsible for stimulating muscle growth), they still offer a sustained release of nutrients into your digestive tract without abrupt glucose surges when compared with animal-sourced proteins like whey.

The Importance Of Timing

When it comes to protein shakes while fasting, timing is key.

Consuming a protein shake without understanding the circumstances may result in insulin levels surging and breaking a fast state.

Although most forms of fasting allow for intakes of non-caloric liquids such as broth and herbal tea or even calorie-free sweeteners, most do not permit consuming any calories with high sugar content — including those found in many commercial protein powders.

This means that if you are planning on an extended period of fasting or want to achieve maximum benefits from your intermittent fasting protocols, then it is critical to understand the implications associated with taking a protein shake at specific times throughout your routine.

The general consensus is that having wheat-based proteins before bed cannot break prolonged fasts due to their low glycaemic index which minimizes the effect their digestion has on blood glucose levels and subsequent increases in insulin production by the body’s cells. (4)

Possible Risks Of Drinking Protein Shakes During Fasting

Consuming protein shakes during fasting is controversial.

Studies suggest that drinking protein shakes may cause an insulin spike in the body, resulting in potential disruption to the fasting period and a reduction in its health benefits [5].

Additionally, depending on how much protein you consume and what type of fast you are undertaking, these drinks may not be beneficial for achieving any weight loss goals.

Furthermore, some people in these studies reported experiencing negative side effects such as digestive issues when consuming large amounts of liquid proteins during fasting.

Generally speaking, most experts and research agree on one fundamental point: when you consume a protein shake, you are breaking a fast as it contains calories. Despite it being in liquid form.

You need to view a protein shake in the same light as you would view a turkey breast, both are low in calories, high in protein, and both are considered food.

Should You Have A Protein Shake After Fasting?

Although having a protein shake during fasting is still up for discussion, having one after breaking your fast has some well-documented health benefits.

Protein shakes designed specifically for consumption post-fasting tend to work best as they are typically low in carbohydrates and fats, but high in quality proteins which are essential for muscle repair and growth.

Research also suggests that protein shakes consumed shortly after waking may enhance fat burning following an overnight fast by stabilizing insulin levels. (6)

Not only could this help with fat loss goals, but it could also potentially reduce cravings later in the day and support hormone balance – all great health advantages.

Additionally, many types of active ingredient found within certain brands of replacements meals enables easy digestion while providing ample amounts of nutrition which can nourish the body faster than other dietary sources following hunger restriction such as caloric restriction or intermittent fasting windows.

Types Of Protein Powders For Fasting With Pros And Cons

When it comes to fasting and protein shakes, the type of powder is key.

Let’s explore the different types of protein powders for fasting- whey protein, casein protein, and plant-based proteins – along with their associated pros and cons.

Whey Protein

Whey protein is one of the most common forms of supplemental protein on the market. It comes in the form of a powder that can be mixed with water or milk, and it provides all nine essential amino acids you need to build muscle plus other beneficial components like calcium, magnesium, phosphorus and B-12 vitamins.

Many people drink whey protein shakes as part of their intermittent fasting regimen because it’s easy to prepare and helps them maintain healthy weight management goals.

However, though some believe that due to its high levels of leucine—an essential branched chain amino acid needed for muscle repair and growth—whey will break your fasted state, studies have shown that this isn’t fully accurate provided you supplement wisely by spreading out the timing between fasted conditions. (7)

There are also potential risks associated with consuming too much whey including digestive upset such as nausea or bloating when consumed in large quantities.

Read more: Do Protein Shakes Make You Poop?

Casein Protein

Casein protein is derived from milk and is a slow-digesting source of protein with anti-catabolic properties, making it a staple supplement for bodybuilders and athletes.

Casein releases amino acids into the bloodstream more slowly than its counterpart whey, providing sustained nutrition over several hours.

Casein may be the preferred choice for those fasting or going to sleep due to its slower rate of digestion that can provide steady energy throughout the night or while intermittently fasting.

The optimal timing for consuming casein protein in relation to intermittent fasting depends on individual goals.

Plant-Based Protein

When choosing a source of protein for fasting, plant-based proteins are often the best option. Unlike animal products such as whey protein powder derived from milk or other dairy sources, plant-based proteins are easily digestible and made from natural ingredients like pea, hemp, brown rice, chia seeds, and flaxseeds.

Plant-based protein powders have a higher content of essential amino acids than their animal-based counterparts while containing less fat and cholesterol. Further, several studies suggest that consuming plant proteins increases post-prandial concentrations of key amino acid precursors when compared with other forms of important dietary proteins. (8)

Additionally, certain types of plant-based supplements contain additional nutrition which is beneficial for individuals who may be on a fast; including chlorophylls – beneficial phytonutrients found in leafy greens which aid in digestion – complex carbs – essential fats – and added minerals such as calcium– all furthering the health benefits associated with this alternative form of supplemental nutrition during intermittent fasting periods.

Best Intermittent Fasting Protein Shakes

It is important to choose the right intermittent fasting protein shake for you, especially considering the different intermittent fasting protocols.

After A Morning Workout

During a fasted morning workout, consuming a protein shake right afterward will not be beneficial as the amino acids in these shakes cause insulin levels to spike and break a fast state.

This prevents your body from entering into ketosis and using stored fat for energy – one of the key elements in achieving weight loss with intermittent fasting.

Instead, post-workout snacks or meals should include fibrous carbs along with healthy forms of fat to maintain blood sugar balance. But you must be aware, this will break your fast completely.

Before Bed

Protein shakes can provide many benefits when taken before bed during fasting. For example, the amino acids contained in protein shakes can help to repair muscle tissue that has been damaged by exercise or other activities throughout the day.

Besides helping with recovery, consuming some carbs and protein before bed can also keep your metabolism going through the night, as well as prepare your body for repair while you’re asleep.

The amount and type of proteins are essential considerations when taking a shake pre-bedtime fast. Casein and certain plant proteins might slow digestive processes down.

Alternatives To Protein Shakes While Fasting

You don’t have to consume protein shakes to get your recommended daily allowance of protein. Opting for whole foods, natural sources of protein, and plant-based proteins such as grains, nuts, and seeds, may be a healthy alternative.

Whole Foods

Whole foods provide a form of nourishment that is difficult to replace, even with protein shakes. Whole foods contain essential vitamins and minerals, plus complex carbohydrates and healthy fats, which are all integral for overall health during fasting periods.

They also help regulate blood sugar levels and keep stomachs fuller for longer through their high fiber content, providing an ideal way to get the nutrition needed while avoiding any hunger or cravings associated with intermittent fasting.

Natural Sources Of Protein

Consuming natural protein sources has become increasingly popular in recent years due to the potential health benefits including improved digestion, muscle development and weight management.

Natural sources of protein include lean meats such as chicken and fish, dairy products like yogurt and cottage cheese, eggs, beans, nuts and seeds. These proteins provide the body with essential building blocks that help promote healthy tissue development.

Additionally, these food items are rich in vitamins and minerals which can aid in regulating blood sugar levels.

Proteins gained from natural sources generally have a slower breakdown rate than those found in supplements or shakes making them a better choice for maintaining energy levels throughout the day or during periods when food is not available such as fasting for religious purposes.

Protein Shake Intermittent Fasting Do’s And Don’ts

– Do consume a low-calorie, high-protein shake during your eating window.

– Don’t eat anything while fasting that contains calories, like protein shakes.


When it comes to using protein shakes while incorporating intermittent fasting into your diet, there are several “dos” that one should keep in mind. First, it is important to ensure that the protein shake chosen contains no sweeteners or added sugars; otherwise, this will break the fast and leave you with unwanted calories.

It is also recommended to take a low-calorie option during feeding windows when insulin sensitivity is high (e.g., shortly after exercising).

Additionally, if calorie restriction is necessary for weight loss purposes, then swapping out meals for drinks such as protein shakes may be beneficial in helping keep hunger at bay–as long as they contain fewer calories than those skipped solid meals would have provided.

Longer-duration fasts tend to require more carbohydrates than intermittent ones due to increased levels of hunger hormones; in these cases, carefully choosing drinks like higher-carbohydrate meal replacements instead of just water might be beneficial since all food sources contribute significantly towards daily nutrient requirements.


When fasting, it’s important to be mindful of what you eat and drink. Protein shakes can provide beneficial proteins but can also interrupt the fast if not consumed properly.

Avoid drinking protein shakes during your fasting window, as these products contain calories that will break your fast and cancel out its benefits.

You should also continue to drink lots of water throughout your day while intermittent fasting with a protein shake – dehydration can have severe consequences for body functions such as digestion.

Additionally, consuming any snacks or other food items in addition to a protein shake during fasting hours can quickly lead into overconsuming calories and breaking the fast too soon.

Common Misconceptions About Drinking Protein Shakes While Fasting

Many people have misconstrued protein shakes and fasting, believing them mutually exclusive. To understand the truth behind these misconceptions, it’s important to dive deeper into how a protein shake affects your fast and if any potential risks are involved in drinking one while fasting.

It’s A Form Of Cheating

Some people believe that drinking protein shakes while fasting is a form of cheating and goes against the fundamental principles of fasting.

This belief comes from the idea that consuming any source of calories, such as those contained in an average protein shake, defeats the purpose of fasting for having adequate nutrition for proper body function.

It’s Necessary For Muscle Building

Consuming protein shakes during fasts can tremendously benefit muscle growth and repair. Protein is an essential macronutrient in the body, playing a key role in maintaining muscle formation and helping muscles to recover faster after strenuous exercise.

When selecting a protein shake to use while fasting, it is important to consider not only the type of powder used, but also when it should be consumed to achieve optimal results.

The best time for drinking a protein shake during intermittent fasting would vary depending on individual goals—for instance, if one’s goal is fat loss or building lean mass then having a high-protein meal before or shortly after ending your fast could maximize these results.

It’s Essential For Meeting Daily Protein Requirements

Consuming a healthy amount of protein during a fast will help maintain existing muscle mass while maximizing fat burning potential with minimal risk of developing nutrient deficiencies.


Whether it is about a specific type of fast, meal replacement shakes, or the importance of timing – these questions offer a deep dive into the most common questions about fasting and protein shakes, to help you make an informed decision on what to do when considering protein shakes during fasting.

How Much Protein Do You Need Per Day?

The amount of protein you need each day depends on several factors, such as age, gender, body size and activity level. Generally speaking, the Recommended Dietary Allowance (RDA) for adults is 0.8 grams per kilogram of body weight in healthy individuals.

For those looking to build muscle or burn fat through exercise, protein intake needs increase significantly due to increased demands from physical activity. For active people such as powerlifters and athletes trying to gain muscle mass or improve athletic performance, 1-2 g / kg body weight may be needed depending on their goal(s).

Do You Need Protein While Intermittent Fasting?

Research has found that people who meet their recommended intakes of protein benefit from improved muscle mass and recovery time after exercise compared to those who skip out on the nutrient.

During longer fasts (24 hours or more), increased levels of stress hormones can lead to catabolism, whereby stored muscles could be broken down if enough dietary protein isn’t eaten regularly over three days or more.

It’s important to note that although too little protein intake causes problems such as poor recovery after physical activity and impaired body composition, large doses may also promote excess insulin release, which would result in breaking a fast temporarily since insulin spikes signal an end to the post-absorptive state required for prolonged periods of fasting.

How To Get Enough Protein While Intermittent Fasting?

Intermittent fasting may be a great way to lose weight and gain energy. But it is essential to make sure you are getting enough protein while doing so, as protein provides numerous health benefits and is important for maintenance of muscles as well as aiding in healthy digestion.

Eating meals high in protein but low in calories is an ideal way to get all the nutrition your body needs without exceeding your calorie goals during periods of intermittent fasting.

Ideally, meals should include at least 20-30 grams of lean proteins such as chicken breasts, fish or eggs while avoiding excess processed carbs like breads and pastas.

For example, scrambled eggs with mushrooms on whole wheat toast make a good breakfast option that’s both tasty and nutritious.

Other options could include oatmeal with grilled salmon or almonds & berries with yogurt parfait for lunch or dinner, respectively – these also provide sufficient amounts of carbohydrates needed to help maintain muscle mass throughout the day.

Can Protein Shakes Help With Weight Loss During Fasting?

Fasting is a popular method for weight loss. However, some individuals may have concerns about how to maintain adequate protein intake while fasting. Protein shakes can be used during intermittent fasts as an alternative source of lean protein.

Research has suggested that increasing dietary protein intake may lead to more significant fat/weight loss when combined with proper diet and exercise regimens. (9)

Can Protein Shakes Break A Fast Completely?

Yes, protein shakes can completely break a fast. Protein contains amino acids that cause an initial rise in insulin levels when consumed because your body needs to process the proteins.

This spike in insulin causes your body to end its fasted state and starts breaking down glycogen stores, rather than drawing on fat to fuel itself. During intermittent fasting, this could mean that you’re not getting the full benefits of being in a fasted state.

What Can I Drink During Intermittent Fasting?

Intermittent fasting involves cycling between periods of eating and periods of not-eating. During the ‘not-eating’ phase, you need to ensure that your body is still getting all the vital nutrients it needs – and one of those nutrients is proper hydration.

Water intake should always be high during fasting, as water helps us feel fuller while aiding in healthy digestion and nutrient absorption.

Other beverages like unsweetened tea or coffee can help retain alertness without breaking a fast due to their lack of calories; however, keep an eye on caffeine intake if this affects your health negatively.

Can You Snack On Protein Shakes While Fasting?

Snacking on protein shakes while fasting is not recommended due to their tendency to spike insulin levels and thus, break the fast. Consuming a protein shake during a window of fasting has the potential to interfere with the metabolic processes that occur for those benefits associated with intermittent fasting diets.

Is Intermittent Fasting Suitable For Everyone?

Intermittent fasting is an increasingly popular dieting strategy that reduces calories for part or whole of the day, usually through restricted eating windows.

While there are potential metabolic and mental health benefits associated with following a structured fasting plan like intermittent fasting, it’s important to note that individuals who have hypoglycemia, high blood pressure or are pregnant should steer clear of fasting diets completely without consulting a doctor first due to possible nutritional deficiencies.

Even if considering trying out intermittent fasting in its more flexible forms, such as time-restricted eating (eating within a specific window) one should make sure their body weight remains stable during this period and overall nutrition intake still meets everyday needs like vitamins & minerals.

Final Verdict: Don’t consume protein Shakes during fasting as they contain calories

As mentioned throughout, the consumption of protein shakes during periods of fasting can break a fast due to the presence of amino acids, which trigger an increase in insulin levels.

Protein shakes, contain calories and will break a fast when consumed within its duration.

Supporting Research

  • Nuttall, F. Q., & Gannon, M. C. (2018). The metabolic response to ingestion of proline with and without glucose. Metabolism Open, 1, 2-11.
  • Frid, A. H., Nilsson, M., Holst, J. J., & Björck, I. M. (2005). Effect of whey on blood glucose and insulin responses to composite breakfast and lunch meals in type 2 diabetic subjects. The American journal of clinical nutrition, 82(1), 69-75.
  • Nilsson, M., Holst, J. J., & Björck, I. M. (2007). Metabolic effects of amino acid mixtures and whey protein in healthy subjects: studies using glucose-equivalent drinks. American Journal of Clinical Nutrition, 85(4), 996-1004.
  • Attinà, A., Leggeri, C., Paroni, R., Pivari, F., Dei Cas, M., Mingione, A., Dri, M., Marchetti, M., & Di Renzo, L. (2021). Fasting: How to Guide. Nutrients, 13(5).
  • Manders, R. J., Koopman, R., Sluijsmans, W. E., van den Berg, R., Verbeek, K., Saris, W. H., … & van Loon, L. J. (2006). Co-ingestion of a protein hydrolysate with or without additional leucine effectively reduces postprandial blood glucose excursions in Type 2 diabetic men. Journal of Nutrition, 136(5), 1294-1299.
  • Jakubowicz, D., Wainstein, J., Landau, Z., Ahren, B., Barnea, M., Bar-Dayan, Y., & Froy, O. (2015). A high-protein breakfast induces greater insulin and glucose-dependent insulinotropic peptide responses to a subsequent lunch meal in individuals with type 2 diabetes. Journal of Nutrition, 145(3), 452-458.
  • Aird, T. P., Davies, R. W., & Carson, B. P. (2018). Effects of fasted vs fed-state exercise on performance and post-exercise metabolism: a systematic review and meta-analysis. Scandinavian Journal of Medicine & Science in Sports, 28(5), 1476-1493.
  • Gorissen, S. H. M., & Witard, O. C. (2018). Plant proteins: Assessing their nutritional quality and effects on health and physical function. Nutrients, 10(12), 1841.
  • Leidy, H. J., Clifton, P. M., Astrup, A., Wycherley, T. P., Westerterp-Plantenga, M. S., Luscombe-Marsh, N. D., Woods, S. C., & Mattes, R. D. (2015). The role of protein in weight loss and maintenance. The American Journal of Clinical Nutrition, 101(6), 1320S-1329S.

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Written By


Nicolette has been a certified dietician and nutritionist for over ten years, whose work has been featured in the likes of Reader’s Digest, Eat This, Not That, Everyday Health, and Shape. She believes in emphasizing a holistic approach toward food and nutrition.