Protein Shakes & Diarrhea: Causes + Fixes Explained

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Protein shakes can be a convenient way to meet your daily protein requirements, but not if you end up experiencing diarrhea as a result.

Why do protein shakes cause diarrhea?  The most common reasons for protein shakes to cause diarrhea are lactose intolerance, sensitivity to sugar alcohols or other additives, sensitivity to higher amounts of fiber, or drinking the shake too quickly.  Rarely, a milk allergy is the culprit for diarrhea after drinking a protein shake.

In this article, I’ll go into more depth on the common reasons protein shakes cause diarrhea.  

Then, I’ll share six simple steps to help you choose a protein powder that doesn’t cause diarrhea.  

This will allow you to enjoy your shake symptom-free, making it easier to get all the protein you need to achieve your health and fitness goals.

6 Reasons Whey Protein Shakes Can Cause Diarrhea

Here are the six reasons why whey protein shakes can cause diarrhea:

  • You have a lactose intolerance
  • The sugar alcohol content is too high
  • There are additives you’re not used to digesting
  • The fiber content is too high
  • You are drinking the protein shake too quickly
  • You have a milk allergy

1. You Have A Lactose Intolerance

Up to 65% of the world’s population is intolerant to lactose, the naturally-occurring form of sugar in dairy milk from cows and goats.  

People who are lactose intolerant do not make the enzyme lactase in their bodies.  This means that they have a harder time digesting lactose and symptoms can include pain, bloating, diarrhea, gas and nausea.  

While whey protein isolate has little or no lactose, whey protein concentrate can have several grams of lactose per serving.  

Depending on severity of the lactose intolerance, even a small amount of lactose in a scoop of whey protein isolate could cause problems.

How to Fix

If you are lactose intolerant, switch to a lactose-free whey protein powder.  Note that even pure whey isolate can still have a small amount of lactose remaining, so if you are extremely sensitive, it is important to look for “lactose-free” in the label.  I recommend VitPro 100% Whey Protein Isolate, Sugar-Free and Lactose-Free.

When buying whey protein, also check the ingredients carefully for whey protein concentrate; this version of whey protein is less costly to manufacture, so supplement companies often make whey protein blends with both isolate and concentrate to keep their costs down.

You can expect to pay more for pure whey protein isolate than a whey protein blend, but having a shake that doesn’t give you diarrhea is well worth it.

2. The Sugar Alcohol Content Is Too HIgh

Sugar alcohols such as sorbitol or mannitol are commonly found in protein shakes because they provide sweetness for a fraction of the calories of sugar.  

The downside is that they can cause digestive upset in sensitive individuals.  

How to Fix

If you are sensitive to sugar alcohols, look for unsweetened protein powders, or protein powders sweetened with sugar or high-intensity sweeteners such as Sucralose, acesulfame potassium or stevia instead.

I also recommend VitPro 100% Whey Protein Isolate, Sugar-Free and Lactose-Free for this reason because it is sweetened only with Sucralose.

3. There Are Additives You’re Not Used To Digesting

Food additives in the form of gums, thickeners and emulsifiers are common in protein powders and ready-made protein shakes to give them a smooth, creamy texture.  

Common examples are acacia, arabic, carob bean, guar, gellan or xanthan gums, carrageenan, and soy and sunflower lecithin.

In sensitive individuals, any one or more of the ingredients above can result in intestinal discomfort including diarrhea.

How to Fix

If you suspect that additives in your protein shake are causing diarrhea, read labels carefully and switch to a brand with little to no added ingredients beyond protein powder.  I recommend Iconic Protein Powder with only four ingredients: milk protein isolate, natural vanilla flavor, monkfruit extract, and sea salt.

This brand is sugar-free, lactose-free, gluten-free, non-GMO and kosher and contains no unwanted additives.

4. The Fiber Content Is Too High 

Both too much and too little fiber have been linked to diarrhea.  Fiber absorbs water and adds bulk to stool, slowing down digestion time and keeping food from moving through the intestines too quickly.  

For people who do not consume enough fiber in their daily diet, missing out on this bulk can mean diarrhea caused by food moving too quickly through the digestive tract.  If their protein shake also does not contain fiber, the problem can be even worse because it adds to the liquids they are consuming.

On the other hand, too much fiber can result in stools that are too soft, which also move too quickly through the digestive tract.  For people facing this problem, a protein shake with added fiber would exacerbate this issue.

How to Fix

If you suspect fiber intake is causing diarrhea, aim for a total daily intake of 25g-28g of fiber for women and 31-34g of fiber for men

Make sure that your protein shake helps you to achieve this target, either by adding fiber to help you reach the minimum, or looking for a brand with no added fiber to avoid exceeding the maximum recommended amounts.

5. You Are Drinking The Protein Shake Too Quickly

Drinking a protein shake too quickly can cause digestive upset including diarrhea by causing your body to send a lot of liquid to the stomach and small intestine all at once to start digesting the large amount of nutrients that were ingested.  

Drawing water into the small intestine can soften stool to the point of diarrhea. 

How to Fix

If you’re drinking your protein shake quickly, slow down and take a break between each mouthful.  Aim for it to take at least 5 minutes for each cup (250mL) of shake, e.g. a 500mL shake should take about 10 minutes to drink.

  • Related Article: Does Creatine Make You Poop? If you are taking whey protein with creatine, the creatine might be the reason why you have diarrhea, not the protein.

6. You Have A Milk Allergy

A milk allergy is different from lactose intolerance: the allergy is an adverse reaction to one or more of the whey proteins in dairy milk.  Only about 0.4% of the adult population in the US has a milk allergy, making it much less common than lactose intolerance.  

How to Fix

If you are allergic to milk, avoid all forms of whey protein and switch to alternative protein powders instead such as egg white or plant-based protein powders (e.g. rice, pea or hemp). An excellent option is Drink Wholesome Unflavored Egg White Protein Powder (only egg whites) which is easy to digest and gut-friendly.

If you have an egg allergy or prefer a plant-based option, check out Vega Protein Made Simple, a pea protein powder naturally sweetened with real organic cane sugar.  It is free of lactose, sugar alcohols, additives and does not contain milk.

6 Simple Steps for Choosing A Whey Protein That Doesn’t Cause Diarrhea

6 simple steps for choosing a whey protein that doesn’t cause diarrhea

Follow the six simple steps below to choose a whey protein that doesn’t cause diarrhea.

Step 1: Mix With Water

First, try mixing your protein powder with just water and no other ingredients to ensure that your reaction truly is to the whey protein powder and not to the liquid it is mixed with or any other added ingredients.

Step 2: Drink Your Shake Slowly

Next, drink your protein shake slowly, taking time between each small sip versus chugging it down in big gulps after your workout.  Slowing down the consumption of your shake could be enough to alleviate your symptoms.

Step 3: Switch to Whey Protein Isolate

If you’re still experiencing issues, the problem could be that you are actually lactose intolerant.  

Whey protein isolate contains little to no lactose, but whey protein concentrate and protein powder blends containing whey protein concentrate will still have lactose.  

Switch to 100% whey protein isolate or look for brands that are explicitly lactose-free.

Step 4: Skip Sugar Alcohols

Be sure your protein powder is unsweetened, or sweetened only with high-intensity sweeteners such as sucralose, acesulfame potassium or stevia instead of sugar alcohols.  

High-intensity sweeteners are so sweet that only a few milligrams are needed to achieve the same sweetness as several grams of sugar or sugar alcohols.  

Step 5: Avoid Additives

Beyond sweeteners, if your whey protein powder is still causing issues, steer clear of any additives such as acacia gum, carrageenan, soy or sunflower lecithin, xanthan gum, etc.  This will let you know if it’s actually an additive that is causing the problem.

Step 6: Try Plant-Based Protein Powder

Although true allergies to dairy milk (an allergy to the whey proteins in milk versus intolerance to lactose, the sugar in milk) are very rare in adults, if the first five steps do not improve your diarrhea, then you could try a plant-based protein powder such as hemp, rice, or pea protein powder.

What To Do If You Still Get Diarrhea After Implementing These Tips

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If you still get diarrhea after implementing these tips, take a break from protein powder and focus on getting your protein from whole foods instead.  It’s also wise to consult with your healthcare provider to rule out other causes of your diarrhea.

Frequently Asked Questions

Is It Common For People To Get Diarrhea After Drinking Whey Protein?

Yes, diarrhea is a common issue after drinking whey protein for people who are lactose-intolerant or allergic to whey protein.  Diarrhea is also common for people who are sensitive to sugar alcohols and/or other food additives such as thickeners or emulsifiers.  Diarrhea also occurs when drinking whey protein too fast.

If I Have Diarrhea After Drinking Whey Protein Does The Protein Go To Waste?

No, not all of the protein goes to waste. The amount of protein that is lost due to diarrhea depends on the type of diarrhea as well as its frequency, severity, and duration.  The effects vary greatly from person to person but rarely does diarrhea cause a complete loss of the calories and nutrients consumed.

Can Drinking Too Much Protein At Once Cause Diarrhea?

Yes, drinking too much protein at once can cause diarrhea, especially if the protein powder contains lactose (common in whey protein concentrate), has been sweetened with sugar alcohols, contains other additives, or is consumed too quickly.  A large serving will increase the amount of offending ingredients.

Why Do Meal Replacement Shakes Cause Diarrhea?

Meal replacement shakes can cause diarrhea for a variety of reasons, depending on their ingredients.  Common culprits include lactose, sugar alcohols, liquid oils, fiber, and food additives such as thickeners and emulsifiers.  The effects are greater for sensitive individuals with allergies or intolerances, or IBS. 

Can You Drink Protein Shakes When You Have Diarrhea?

Yes, you can drink protein shakes when you have diarrhea.  If you have a stomach bug that is causing diarrhea, chances are that you could be experiencing nausea too, which can make it hard to eat solid food and keep it down, and both cause dehydration.  Protein shakes can help provide needed nutrients and hydration.

Other Whey Protein Resources

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About The Author

Lauren Graham

Lauren Graham is a Precision Nutrition Level 1 certified nutrition coach. She focuses on helping busy professionals balance healthy eating and purposeful movement.  Lauren has a background in competitive swimming and is currently competing as a CrossFit athlete.  She has a passion for training, teaching, and writing.