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Can I drink a protein shake after a fast?


Intermittent fasting has become an increasingly popular diet and lifestyle choice. It involves cycling between periods of fasting and eating. Many people wonder if it’s okay to drink a protein shake during the eating window or immediately at the end of a fast. There are a few things to consider when deciding whether a post-fast protein shake is right for you.

What is Intermittent Fasting?

Intermittent fasting (IF) is an eating pattern that involves regular fasting periods. Some popular approaches include:

  • 16/8 method: Fast for 16 hours per day, eat during the remaining 8 hours.
  • 5:2 diet: Eat normally 5 days per week, restrict calories to 500–600 per fast day on 2 days.
  • Alternate day fasting: Fast every other day.
  • The Warrior diet: Eat small amounts of raw fruits and vegetables during the day, one large meal at night.

IF has been associated with benefits like weight loss, improved metabolism, reduced inflammation, and increased longevity. The fasting period triggers ketosis, fat burning, and other favorable changes. However, how you break your fast is also important.

Benefits of Protein Shakes

Here are some of the top benefits of protein shakes:

Muscle Growth and Recovery

Protein is essential for building and repairing muscles. Consuming protein shortly after exercise helps restore damaged muscle fibers. Protein shakes provide a convenient way to get high-quality protein.


Protein is the most filling macronutrient. Drinking a protein shake can help satisfy hunger and prevent overeating. One study found that intermittent fasters who had a protein shake 90 minutes before their main meal ate 20% fewer calories when mealtime arrived.

Weight Loss

Due to its effects on fullness and muscle growth, protein is the king of weight loss nutrients. Numerous studies show that high-protein diets boost metabolism and promote fat burning. Protein shakes provide an easy way to increase daily protein intake.


Protein powders offer a quick, portable way to get protein on-the-go. They require minimal prep and can be consumed anywhere. Protein shakes are easy to drink during busy mornings or post-workout.

Is It OK to Drink a Protein Shake While Fasting?

Technically, anything other than plain water (or black coffee/tea) breaks a fast. However, a small number of calories, especially from protein, won’t interfere dramatically with fasting benefits.

Here are a few points to consider:

  • Aim to keep calories under 50. Opt for a shake with 100 calories or less.
  • Choose a pure protein powder without added sugars, fat, or excessive carbs.
  • Only have 1 serving. Don’t overdo protein intake.
  • Wait until at least 16 hours of fasting. During shorter fasts, stick to water.

While a small protein shake won’t sabotage your fast, it’s ideal to wait until your eating window if possible.

Benefits of a Post-Fast Protein Shake

Here are some of the biggest benefits of having a protein shake immediately or shortly after ending a fast:

Stimulates Muscle Protein Synthesis

During the post-absorptive state of a fast, muscle protein synthesis drops while muscle protein breakdown increases. Consuming protein flips this switch. Leucine, an amino acid found in protein powders, is particularly effective at stimulating muscle protein synthesis.

Replenishes Lost Amino Acids

Prolonged fasting leads to the breakdown of muscle proteins into individual amino acids for fuel. A post-fast protein shake provides amino acids to help restore depleted protein stores.

Boosts Metabolism

Protein has a high thermic effect. Your body burns calories breaking down and digesting protein. Having a protein shake after a fast helps counter the drop in resting metabolism that can occur with fasting.

Reduces Cravings and Overeating

Blood sugar and insulin tend to drop during fasting. This can lead to cravings, hunger, and impulse eating when the fast ends. A post-fast protein shake helps stabilize blood sugar and insulin, reducing the urge to binge.

Time of Protein Intake Benefits
During the Fast
  • Provides nutrients to preserve muscle
  • Blunts drop in metabolism
  • Eases hunger pains
Immediately After the Fast
  • Boosts muscle protein synthesis
  • Replenishes amino acid stores
  • Stabilizes blood sugar
  • Reduces cravings and appetite
30-60 Minutes Post-Fast
  • Maximizes muscle protein synthesis
  • Avoids spike and crash in blood sugar
  • Provides satiety before a meal

Optimal Time to Drink a Protein Shake

Based on the available research, the ideal time to have a protein shake is 30-60 minutes after ending your fasting period.

Here’s why this timing is best:

  • Allows maximal muscle protein synthesis. Muscle protein synthesis peaks around 1 hour post-protein ingestion.
  • Provides satiety before a meal, which reduces calorie intake.
  • Preventsblood sugar spikes and crashes.
  • Has minimal impact on ketosis for those following keto intermittent fasting.

Drinking a shake immediately after a fast offers some benefits, but waiting 30-60 minutes allows more time for protein absorption.

How Much Protein Should You Consume After Fasting?

Most research onprotein intake during intermittent fasting is based on amounts of around 20-30 grams. here are some general protein intake guidelines following a fast:

  • Women: 20-25 grams
  • Men: 25-30 grams
  • Athletes/Bodybuilders: Up to 40 grams

Aim for a moderate serving of high-quality protein. Going overboard on protein can suppress autophagy and ketosis.

Best Protein Powders to Break a Fast

The type of protein you choose matters too. Here are some of the best options:

Whey Protein

Wheyprotein, particularly whey isolate, is quickly digested and absorbed. It rapidly elevates muscle protein synthesis and amino acid levels.

Casein Protein

Casein protein coagulates in the gut, resulting in a slower release of amino acids. This makes itideal for maximizing muscle protein synthesis over several hours.

Collagen Protein

In addition to muscle protein, collagen supplementationcan help rebuild connective tissues impaired by fasting. It provides types 1 and 3 collagen.

Pea Protein

For those who can’t or prefer not to eat dairy, pea protein is a plant-based option. It’s rich in muscle-building branched-chain amino acids.

Hemp Protein

Hemp protein delivers protein along with fiber, omega-3s, and minerals. The fiber helps controlblood sugar when breaking a fast.

Type of Protein Key Benefits
Whey Rapidly digested, quickly increases amino acids and stimulates MPS
Casein Slow release provides sustained elevation in amino acids
Collagen Repairs connective tissues damaged by fasting
Pea Vegan protein high in muscle-building BCAAs
Hemp Plant protein with fiber, omega-3s, minerals

Sample Post-Fast Protein Shakes

Here are a few simple protein shake recipes to try after ending a fast:

Chocolate Peanut Butter Shake

  • 1 scoop chocolate whey protein
  • 1 tablespoon peanut butter
  • 1 cup unsweetened almond milk
  • 1/2 banana
  • Ice cubes

Vanilla Collagen Shake

  • 1 scoop unflavored collagen peptides
  • 1 scoop vanilla whey protein
  • 1 cup coconut milk
  • 1/4 cup blueberries
  • 1 teaspoon cinnamon
  • Stevia to taste

Matcha Protein Smoothie

  • 1 scoop unflavored whey protein
  • 1 cup unsweetened almond milk
  • 1 tablespoon matcha powder
  • 1 frozen banana
  • 1 handful baby spinach
  • 1/4 avocado

Precautions with Post-Fast Protein

While protein is beneficial after fasting, there are a few precautions to keep in mind:

  • Don’t overdo protein intake. Too much protein can suppress muscle building and fat burning.
  • Avoid adding extra carbs, sugars, and fat.
  • Time your protein shake properly, starting 30-60 minutes after your fast.
  • Stay hydrated and spread protein intake throughout the day.
  • If you feel nauseous or ill after protein, reduce the amount or wait longer between your fast and protein shake.

Should You Workout Before or After Breaking a Fast?

You can exercise during or after a fasting period. Here is a comparison:

Benefits of Exercising Before Eating

  • Burns more fat for fuel when glycogen stores are depleted
  • Increases metabolic rate for up to 24 hours
  • Doesn’t require pre-workout nutrition

Benefits of Exercising After Eating

  • Better workout performance and strength
  • Increased muscle protein synthesis from pre-workout protein
  • Reduced risk of overtraining, fatigue, or dizziness

If doing intense training, consuming 20-40 grams of protein before your workout is recommended. For lighter exercise, working out in a fasted state can be beneficial.


Having a protein shake after ending a fast can help stimulate muscle growth, restore depleted amino acids, boost metabolism, and reduce cravings.

Aim for 20-40 grams of a fast-absorbing protein like whey or casein around 30-60 minutes after finishing your fast for optimal results. This feeding timing, along with proper protein intake, allows you to reap the most benefits from your fasting periods.