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5 Reasons Protein Powder Can Mess With Your Digestion & What To Do

Melissa Boufounos, CHN
Author: Expert reviewer:
April 24, 2023
Melissa Boufounos, CHN
Certified holistic nutritionist
By Melissa Boufounos, CHN
Certified holistic nutritionist
Melissa Boufounos is a certified holistic nutritionist, nutrition writer, and lifelong athlete in the greater Ottawa, Ontario, Canada area. She specializes in sports nutrition and works with teen hockey players and competitive obstacle course race athletes in her virtual private practice MB Performance Nutrition.
Lauren Torrisi-Gorra, M.S., RD
Expert review by
Lauren Torrisi-Gorra, M.S., RD
Registered Dietitian
Lauren Torrisi-Gorra, MS, RD is a registered dietitian, chef, and writer with a love of science and passion for helping people create life-long healthy habits. She has a bachelor’s degree in Communication and Media Studies from Fordham University, a Grand Diplôme in Culinary Arts from the French Culinary Institute, and master's degree in Clinical Nutrition and Dietetics from New York University.
April 24, 2023
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Protein is an essential macronutrient that plays a role in maintaining various bodily functions, including muscle growth and repair, hormone production, and immune function. While adequate protein intake is important for optimal health, some people report that consuming protein powder makes them poop more, makes them constipated, or causes other digestive issues.

We reached out to nutrition and gut health experts to explore the potential effects of protein on bowel movements and how protein powder may impact digestion. 

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How your body digests protein

When you eat food, your body has to break it down into smaller, usable forms that can be moved around the body. Proteins are broken down into amino acids.

Digestion begins in the mouth as you chew food into smaller pieces. From there, digestive enzymes in your saliva start to break down carbohydrates and fats. Protein digestion begins in the stomach, where pepsin is secreted to break down protein into smaller peptides. 

"The stomach produces hydrochloric acid (HCl) and pepsinogen, an inactive form of the enzyme pepsin. The acidic environment of the stomach activates pepsinogen to pepsin, which starts breaking down proteins into smaller peptides (short chains of amino acids)," explains Ashley Sauvé, CHN, a certified holistic nutritionist and herbalist specializing in digestive health.

"Adequate stomach acid is very important for protein digestion, and low stomach acid can slow down protein digestion," she adds. 

Protein powder is generally digested in the same way as dietary protein. However, the absorption rate may differ depending on the type of protein powder and what it's mixed with.

For example, whey protein is absorbed faster than casein protein. And since liquids digest faster than whole foods, a protein powder consumed without additional fat or fiber will be absorbed faster than dietary protein. 

Why protein powder can cause diarrhea/constipation

Depending on the ingredients or your potential intolerances, you could experience constipation or loose stools when you consume protein powder. Here are a few things reasons protein may make you poop more or less often and what to do about them:

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You're not eating enough fiber.

"Fiber has so many roles in the gut," says Sauvé. "It improves gut motility (helps keep things moving in the gut) and feeds beneficial bacteria." 

Consuming a high-protein diet may crowd out other macronutrients, like carbohydrates, which provide beneficial fiber, vitamins, and minerals. So it's not what you're eating that's the problem (protein); it's what you're not eating (fiber) that can lead to constipation. 

"If less fiber is consumed to make more room for protein, then there is a higher chance of constipation, which can also lead to more gas," notes nutritionist and gut health expert Kim Kulp, RDN.

Daily fiber needs for adults range from 21 to 38 grams, depending on age, gender, and life stage. Unfortunately, the average American only consumes1 about 17 grams of dietary fiber daily, with people following low-carbohydrate diets eating even less. 

What to do

Ensure you're getting enough fiber by eating plenty of berries, citrus, whole grains, legumes, nuts, and seeds and supplementing with a fiber powder if needed.
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It contains more fiber than you're used to.

On the flip side, plant-based protein powders like hemp protein are higher in fiber, which can affect digestion differently than animal-based protein powders that contain no fiber. 

"Since more than 95% of the American population does not consume enough dietary fiber, there is a chance that excess hemp protein powder could result in a quick jump in dietary fiber intake, which could lead to gastrointestinal issues, like bloating and gas," Nichole Dandrea-Russert, M.S., RDN, author of The Fiber Effect, previously told mindbodygreen.

For people with chronic constipation or bowel diseases, an increased fiber intake can worsen constipation2 and its associated symptoms. 

What to do

If plant proteins aggravate your stomach, try a protein powder that is lower in fiber like whey.
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You're lactose intolerant.

"Protein powder can have many different sources, and if someone has a food intolerance, they might experience gastrointestinal upset when consuming protein powder derived from that food," says Sauvé. "For example, individuals with a lactose intolerance might experience loose stools after consuming whey or casein protein." 

It is estimated that 65 to 75% of the world's adult population is lactose intolerant3, many of which are undiagnosed. Common signs of lactose intolerance include diarrhea, bloating, and gas. 

"Whey is a popular protein powder and does contain lactose, which some people may have an issue with," says gut health nutritionist Amanda Sauceda, M.S., RDN.

While whey protein powders typically have few added ingredients, vegan protein powders could contain a blend of different plant sources and other herbs or ingredients you might not realize are causing a reaction.  

What to do

If you have issues with whey protein powder, try a whey isolate powder that is lower in lactose or a plant protein powder with a clean ingredient list.
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It contains artificial sweeteners.

Many protein powders contain sweeteners (low-calorie sugar substitutes) that are considered safe for consumption, but that doesn't mean they come without side effects.

The effects of sweeteners on gut microbiota need to be further studied; however, in a review of experimental studies and clinical trials, only saccharine, sucralose, and stevia changed the composition of the gut microbiota4

"Some protein powders contain polyols, such as sorbitol or erythritol, to add sweetness without adding sugar," says Kristin Draayer, M.S., RDN, CPT. "These artificial sweeteners can have a laxative effect5 if consumed in large amounts, potentially leading to loose stools." 

What to do

Switch to a protein powder that does not contain artificial sweeteners like sorbitol or erythritol.

It's disrupting your gut microbiome.

The gut microbiome is the collection of microorganisms that reside in your digestive tract and play a critical role in health. Protein can affect the gut microbiome6 in various ways, both positively and negatively. 

"A healthy gut includes a greater diversity of microbes," says Kulp. "These microbes protect the lining of the intestines, improve immune function, and can reduce inflammation7, which can decrease the risk of heart disease, diabetes, and cancer."

One study that investigated the effects of a protein supplement on the gut microbiota8 of endurance athletes found that it led to a decrease in health-promoting bacteria like Blautia, Roseburia, and Bifidobacterium longum. These bacteria are associated with improved immune function, gut barrier function, and anti-inflammatory properties. However, the long-term consequences of the decrease in these bacteria for gut health are unknown. 

In another study, dietary protein intake and exercise were associated with a higher diversity of gut microbiota in professional rugby players9. More research is needed to determine how altering gut microbiota diversity affects gut health and overall health outcomes10

The source of the protein can also influence the gut microbiome. Plant-based proteins likely have more effect on microbiota11 than animal proteins because of their fiber content. Some protein powders, such as whey protein isolate, contain lactoferrin and immunoglobulins that can act as prebiotics12

What to do

Overall, the effects of protein powder on the gut microbiome are complex and may vary depending on the type of protein powder you use, your overall diet and lifestyle, and other factors. So try a few protein powders before choosing the one that feels best to your system.

You have low stomach acid.

Pepsin is the main enzyme involved in protein digestion13, requiring an acidic environment to be activated. Not having enough stomach acid to break down protein can lead to digestive issues like gas or bacterial overgrowth

According to Sauvé, low stomach acid is quite common and can be triggered by stress or nutrient deficiencies. She recommends taking a tablespoon of apple cider vinegar in a little water before meals to help maintain an acidic stomach environment, which is optimal for protein digestion.

What to do

Introduce foods into your diet that help maintain an acidic stomach environment—like apple cider vinegar—if you suspect this is an issue for you.

Digestibility of plant vs. animal protein powders

In general, animal proteins are more easily digested than plant proteins.

However, evidence suggests14 that some plant-based proteins, like hemp, have protein digestibility scores equal to or greater than other grains, nuts, and pulses. In another study15, the protein digestion of eight protein sources was compared. Whey protein isolate and pigeon peas had the highest amino acid release. 

"Whey protein is considered a fast-digesting protein16, which means that the protein can be broken down quickly and then used by the body," explains Sauceda. "Plant-based protein powders are more likely to also have fiber that may slow down digestion, but that isn't necessarily a bad thing. Fiber helps you stay fuller longer and your body will still get the amino acids you need." 


Animal protein is usually easier to digest than plant protein (as long as you're not lactose intolerant). Of the plant proteins, hemp and pea are typically the easiest to digest.

Safe ways to eat a higher protein diet

While most active people should aim to consume at least 100 grams of protein per day for optimal health, increasing your protein intake shouldn't come at the expense of digestive discomfort. 

Here are some tips to help you consume protein powder and whole food proteins in a way that won't cause stomach upset: 


Experiment with different types of protein powders.

There are so many different types of protein powder available on the market. If the one you're using hurts your stomach, try another brand or protein source. 

"If you're having 'protein poops' from a protein powder supplement, try switching to a different source to rule out an intolerance to the one you're using now," says Sauvé. "Be sure to check for sugar alcohols and other additives, which could be triggering digestive issues." 


Add fiber to your protein shake.

Sauvé suggests consuming protein powder alongside fiber to prevent loose stools (for example, in a smoothie with high-fiber ingredients like blackberries). "Most people overestimate the fiber content of foods, so it can be helpful to track the foods you're eating for a few days to ensure you're hitting your target."

Adding fiber to protein shakes is a simple and effective way to increase dietary fiber intake and reduce the risk of digestive problems associated with protein powder consumption. 


Eat a balanced diet.

Athletes and fitness enthusiasts might inadvertently follow dietary strategies that adversely impact the gut microbiota17.

Eating adequate dietary fiber, a variety of protein sources, healthy fats, and a wide range of vitamins and minerals has shown promising results in optimizing gut and overall health. 

"While we need protein for our muscles, cells, and immune systems, we also need plant nutrients. It's the antioxidants and fibers that are in fruits, vegetables, whole grains, nuts, seeds, and legumes that work as prebiotics, feeding our good gut microbes so they can improve our health," says Kulp. "The combination of protein and a variety of plant foods will give you and your microbes the food needed for a healthy gut and healthy poops." 


Drink enough water.

When you consume a lot of protein, excess nitrogen is flushed with fluids and water. If you aren't drinking enough water, this could lead to mild dehydration, which can affect your bowel movements. 

Adequate hydration also helps fiber do its job properly. Fiber absorbs water as it passes through your digestive tract to soften your stools and prevent constipation. If you are increasing your fiber intake or consuming plant-based protein powders high in fiber, drinking enough water is essential.


Follow serving instructions.

It's always best practice to follow the serving instructions and directions of the supplements you are using. The proper ratio of liquid to powder could help you avoid gastrointestinal distress.

On that note, don't dry-scoop your supplements. (Dry-scooping is a popular TikTok trend where people consume powder supplements like pre-workout or protein powder without liquid.) Along with the risk of aspiration (getting powder in your lungs), dry-scooping your protein powder can cause digestive problems.


Does protein affect bowel movements?

Consuming protein in moderation as part of a balanced diet is generally beneficial for gut health. Still, some people may experience changes in bowel movements when using certain types of protein powder or when eating excess dietary protein.  

Why does protein make me poop more?

Some people may experience protein poops when consuming protein powder, mainly if they are sensitive to the ingredients in the product. Artificial sweeteners and sugar alcohols added to protein powder can irritate the gut and make you poop more.

What are the signs of too much protein?

Insufficient evidence supports the myth that excess protein damages the kidneys or that protein negatively impacts health. High-protein foods may be higher in total fat and saturated fat, which can lead to high blood cholesterol lipids and heart disease. Excessive protein can mean you are not making enough room in your diet for whole plant foods that provide different vitamins and minerals, fiber, and antioxidants. Healthy adults can tolerate eating 2g/kg protein per day and up to 3.5 g/kg for a prolonged period. There's no consensus on a safe upper limit of supplemental protein intake, but one to two servings per day are unlikely to cause harm. 

The takeaway

Protein in and of itself shouldn't cause digestive problems for most people. Certain types of protein powder or ingredients in protein powder can lead to digestive issues such as bloating, constipation, or diarrhea in some people.

To minimize these side effects, consume protein powder in moderation alongside a well-balanced diet, stay well hydrated, and choose protein powders that don't contain artificial sweeteners or other ingredients you might be sensitive to.