Fasting on Protein Shakes (Don’t Make This Mistake)

Does fasting on protein shakes work? It might sound like a good idea to have protein shakes during your fast, but you’ll want to check this out first.

Intermittent fasting has become an very popular dieting style in recent years. Basically, you cycle between periods of eating and fasting. Intermittent fasting is a great way to burn stubborn fat, lose weight and improve your health.

It can be confusing knowing what exactly will break your fast. One of the most common mistakes is drinking or eating certain foods or beverages that break the fast. The last thing you want to do is unknowingly ruin your fast by eating or drinking the wrong thing.

To get the best results with intermittent fasting, you’ll need to know what exactly breaks or boosts your fast. Here you’ll discover if you can fast on protein shakes or if it’ll ruin your results.

Can You Drink Protein Shakes While Intermittent Fasting

The short answer is no, you can’t drink protein shakes when intermittent fasting. Drinking a protein shake will break your fast because it’ll spike your insulin levels. 

Consuming anything that causes an insulin spike in your body will effectively break you fast. The goal of intermittent fasting is to drive your insulin levels low, so your body has to start utilizing your fat stores for fuel. 

Insulin is the hormone that helps your body absorb sugar from carbohydrates, and when it spikes it can cause your blood sugar levels to rise quickly and result in fat storage. When fasting, you want to minimize insulin spikes so your body can better utilize stored fat for energy.

Let’s say you exercise in the morning in the middle of your intermittent fasting window. Would it be okay to have a protein shake in the morning while still fasting?

Having a protein shake anytime during your fast will increase insulin and thus break it. The post-workout protein window can extend for many hours after and you don’t need to follow the old school “anabolic window” of 300-60 minutes post-workout.

Water Fast vs Protein Shake Fast

A pure water fast is a form of intermittent fasting in which only water is strictly consumed during the fast. With a water fast, no other food or beverages are allowed, not even tea or coffee making it difficult for many to make it through the fast.

Water fasting will maximize the results you get with intermittent fasting, but for many it’ll be tough to make it through the fast due to the hunger pangs. So if your goal is mainly to lose weight then you can use a modified “dirty fast” instead.

Dirty fasting allows you to have some beverages that don’t spike your insulin and are less than 50 calories in total. Drinking coffee and tea would be approved and will still allow you to get results from fasting without ruining it.

In some ways, a modified dirty fast can even produce better results. For example, the caffeine in coffee and teas can boost your metabolism, enhancing weight loss. They’ll also reduce hunger, making it easier to get through your fasting window and increasing adherence.

My favorite trick is to add C8-MCTs to your morning coffee when fasting. These particular type of MCTs are quickly converted into ketones and help to flip the metabolic switch and jumpstart your body’s fat burning.

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Another modified form of fasting is a protein shake fast. This is when you’re fasting but you are consuming nothing other than protein shakes. Protein can help you feel fuller for longer and reduce muscle loss from extended fasts.

Protein shake diet fasting won’t be as effective as a pure water fast or even as much as a dirty fast with coffee, tea, and MCTs. Since protein does spike insulin, it’ll take away some of the benefits of fasting. But if it allows you to go longer with fasting, then the calorie reduction will result in weight loss, especially if you use it as a meal replacement over eating a higher-calorie meal.

Protein Shakes During Fasting

If weight loss is your primary goal, then you can strategically use protein shakes during fasting for better results. For instance, you could use a low-calorie protein shake to replace one of your meals during your feeding window.

Adding a protein shake to your daily diet plan can quickly and easily boost your protein intake. A high-protein diet effectively burns fat, loses weight, and builds lean muscle to tone the body. Most have trouble meeting the recommended daily protein intake, so drinking protein shakes can be a simple solution.

How much protein should you have daily? Ideally, you’ll consume 0.8 grams of protein per pound of body weight. So if you weigh 150 pounds, you should consume 120 grams of protein (150 x 0.8).

If you’re having trouble making it through your fasting window, adding a protein shake can help. You’ll be able to give your body some leeway to fight the hunger pangs while still not eating a meal. While it will spike your insulin and thus break your fast, you’ll still be training your body to fast for longer.

The main reason many give up on intermittent fasting is the hunger. It’s better to have a protein shake and still fast for 16 hours a day than to binge eat because you get too hungry. By just having a protein shake, your stomach will start to shrink, and your body will have an easier time adapting to eating less.

Best Protein Shake for Intermittent Fasting

While you don’t technically need protein shakes they do make it easier and faster to meet your daily protein needs. Protein shakes are essentially just the macronutrient protein that your body utilizes to build muscle.

It’s no different if you ate a chicken breast for the protein content. Protein shakes can help you lose weight by boosting metabolism, increasing satiety, and improving lean body composition (less fat, more lean muscle mass).

But don’t worry about becoming a giant muscle-bound bodybuilding from drinking protein shakes. Bodybuilders lift a high volume of heavier weights, consume a lot of calories, and use other means to bulk up.

But there are many protein shakes on the market that are rather high calorie, high carb, and use a lot of artificial fillers. So it’s important only to use a high-quality protein so you’re not sabotaging your results and health.

Here are some criteria to look for in protein shakes:

  • ~25 grams of protein per serving (max your body can absorb at one time)
  • low calorie
  • low carb and low sugar
  • cold-processed and micro-filtered to prevent denaturing
  • blend of time-released proteins to vary the absorption rate
  • no artificial fillers or flavorings
  • sourced from non-GMO, hormone-free, grass-fed cows

My pick is BioTrust’s Low-Carb Protein. It contains 24 grams of protein per serving, it’s only 150 calories, 1 gram of sugar, and less than 4 grams of net carbs.

This protein contains a blend of four premium proteins that delay absorption, lowering any insulin release and making you feel fuller for longer. It’s certified hormone and antibiotic free from pasture-raised cows. Lab-tested to ensure there’s nothing artificial. And it’s a cold-processed, microfiltered, and non-denatured protein.

Oh, and it’s the best-tasting protein powder I’ve had. It tastes delicious and is a big plus considering how many protein powders taste like chalk. It also contains ingredients making it easier to digest and absorb nutrients.

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  • gut friendly prebiotics + digestive enzymes for maximum protein absorption and easy digestion


If you drink protein shakes outside your intermittent fasting eating window, then it will technically break your fast. A pure water fast only allows you to consume strictly water, and doesn’t even allow black coffee.

But if weight loss is your main goal with fasting, then a dirty fast will still produce great results while allowing you to consume protein shakes. You can add in a protein shake break towards the end of your fast if the hunger is overwhelming. It’ll be better than binge eating, and it’ll help your body adapt to more extended periods without eating.

Not all protein shakes are good for you though. Many are high in calories, carbs, sugars, and artificial fillers. When consuming protein shakes it’s best to find a protein powder that is high quality while also tasting good so you’ll continue drinking it.

A quality protein powder can make getting more protein into your intermittent fasting plan much easier. You can lower your daily calorie intake and increase weight loss by replacing a meal you’d otherwise eat. So it’s best to consume the protein outside your fasting period, but if you have to then it’s better than going hunger crazy and giving up your fast completely.