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

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.

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.

"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.

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.

"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.

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. 

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. 

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. 

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. 

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. 

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. 

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."

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. 

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. 

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.

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.