According to Gram Research analysis, eating poorly digestible bovine plasma protein produces 44% more p-cresyl sulfate in your blood compared to easily digestible whey protein isolate, along with higher levels of other protein fermentation products. This randomized controlled trial of 13 healthy adults found that different protein sources create different amounts of waste products when gut bacteria break them down, even when the total protein amount is identical. The differences appear to come from the amino acid composition of the proteins rather than just how easy they are to digest.
A new study compared how your body handles two different types of protein powder: bovine plasma protein (a less digestible option) and whey protein isolate (a highly digestible option). Researchers found that when people ate the less digestible protein, their bodies produced higher levels of certain waste products from protein breakdown in their blood and urine. These metabolites come from how bacteria in your gut ferment undigested protein. The study suggests that the type of protein you consume matters for what happens in your digestive system, even when you eat the same amount of protein overall.
Key Statistics
A randomized controlled trial of 13 healthy adults published in the American Journal of Clinical Nutrition in 2026 found that bovine plasma protein consumption increased blood p-cresyl sulfate levels by 44% compared to whey protein isolate (41.0 versus 28.5 units).
According to research reviewed by Gram, consuming poorly digestible bovine plasma protein for 7 days increased urinary p-cresyl sulfate by 22% and phenylacetyl-L-glutamine by 32% compared to easily digestible whey protein isolate in a crossover dietary intervention.
A 2026 controlled dietary intervention found that protein source affected plasma concentrations of four different fermentation metabolites, with bovine plasma protein producing 33-44% higher levels of p-cresyl sulfate, phenyl sulfate, phenylacetyl-L-glutamine, and indoxyl sulfate compared to whey protein isolate.
In a randomized crossover trial, bovine plasma protein consumption tended to prolong colonic transit time compared to whey protein isolate, suggesting that harder-to-digest proteins spend more time in the large intestine where bacteria ferment them.
The Quick Take
- What they studied: Whether different types of protein powder create different waste products when your body breaks them down, and how this affects what shows up in your blood and urine.
- Who participated: Fifteen healthy adults (13 completed the study) who tried eating two different protein sources for one week each, with a break in between.
- Key finding: Bovine plasma protein (harder to digest) produced 44% more p-cresyl sulfate in the blood compared to whey protein isolate (easier to digest), along with higher levels of other protein breakdown products.
- What it means for you: The type of protein you eat affects how your gut bacteria process it and what waste products end up in your body. While this study is small and preliminary, it suggests choosing easily digestible proteins might reduce certain metabolites that could potentially affect your health over time.
The Research Details
This was a randomized controlled crossover trial, which is a strong research design. Fifteen healthy adults participated, and each person tried both protein sources in random order. For 7 days, participants ate 30 grams of either bovine plasma protein (a protein that’s hard for your body to digest) or whey protein isolate (a protein that’s easy to digest). They then took a 7-day break and switched to the other protein. Researchers collected blood, urine, and stool samples to measure what happened to the protein in each person’s body.
The crossover design is powerful because each person serves as their own comparison, researchers can see how the same person’s body responds to each protein type. This reduces the effect of individual differences between people. The study measured specific waste products that form when bacteria in your large intestine ferment undigested protein, which is the main focus of this research.
Understanding how different proteins affect your gut is important because some of these waste products might influence your long-term health. When protein reaches your large intestine undigested, bacteria ferment it and create metabolites (chemical byproducts). Some of these metabolites, like p-cresyl sulfate, have been studied in relation to kidney and heart health. By comparing two proteins with different digestibility levels, researchers can understand whether the type of protein matters for these processes.
This study has several strengths: it’s a controlled trial where participants ate measured amounts of protein, it used a crossover design so each person was their own control, and it measured actual biomarkers in blood and urine rather than just asking people what they ate. However, the sample size is small (13 people completed it), which means results might not apply to everyone. The study was also short (only 7 days per protein), so we don’t know what happens with longer-term consumption. All participants were healthy adults, so results might differ for people with digestive issues or other health conditions.
What the Results Show
When people ate bovine plasma protein (the harder-to-digest type), their blood contained significantly higher levels of several protein fermentation products. Specifically, p-cresyl sulfate was 44% higher (41.0 versus 28.5 units), phenyl sulfate was 17% higher, phenylacetyl-L-glutamine was 35% higher, and indoxyl sulfate was 33% higher. These same patterns appeared in urine samples as well, with p-cresyl sulfate 22% higher, phenyl sulfate 40% higher, and phenylacetyl-L-glutamine 32% higher during bovine plasma protein consumption.
Interestingly, the researchers initially expected these differences because bovine plasma protein is harder to digest. However, when they tested how well each protein was broken down in laboratory conditions, the digestibility was actually quite similar between the two proteins (32.6% versus 26.3%). This suggests the differences in fermentation products came from the different amino acid composition of the proteins, not just from how easy they are to digest.
The study also found that bovine plasma protein tended to slow down how quickly food moved through the colon (the large intestine), though this difference wasn’t quite statistically significant. Other measures like fecal ammonia levels and the diversity of gut bacteria didn’t differ between the two protein sources.
The researchers measured several secondary outcomes to understand the full picture. Gut microbiome diversity (the variety of bacteria in your intestines) didn’t change between the two protein sources, suggesting that one week of different protein consumption doesn’t dramatically alter your bacterial community. Fecal ammonia, another waste product from protein fermentation, also didn’t differ significantly. However, colonic transit time (how long food takes to move through your large intestine) showed a trend toward being longer with bovine plasma protein, which could explain why more undigested protein reached the bacteria in the colon.
This research builds on existing knowledge that protein fermentation in the colon produces metabolites that enter the bloodstream. Previous studies have suggested that some of these metabolites, particularly p-cresyl sulfate and indoxyl sulfate, may have effects on kidney and cardiovascular health. However, most previous research didn’t carefully compare how different protein sources affect these specific metabolites. This study is one of the first to directly test whether protein digestibility and amino acid composition matter for these fermentation products. The findings align with the theory that harder-to-digest proteins lead to more bacterial fermentation, but add the important detail that amino acid composition may be equally or more important than digestibility itself.
The study is small with only 13 participants who completed it, which limits how much we can generalize the findings to larger populations. All participants were healthy young adults, so results might not apply to older adults, people with digestive disorders, or those with kidney or heart disease. The intervention was only 7 days long, so we don’t know if these effects persist with longer-term consumption or if the body adapts over time. The study used isolated protein powders rather than whole foods, so results might not apply to eating protein from chicken, beans, or other natural sources. Additionally, while the study measured fermentation products, it didn’t directly measure whether these products caused any health effects, it only showed that different proteins produce different amounts of these chemicals.
The Bottom Line
Based on this research, there’s moderate evidence that choosing easily digestible proteins (like whey protein isolate) over poorly digestible proteins (like bovine plasma protein) may reduce certain fermentation metabolites in your blood and urine. However, this is a single small study, so these findings should be considered preliminary. If you’re concerned about protein fermentation products, particularly if you have kidney disease or cardiovascular concerns, discussing protein choices with your doctor or dietitian would be wise. For most healthy people, the practical difference from this study is unclear, and protein quality, total protein intake, and overall diet quality remain more important factors.
People with kidney disease or those at risk for cardiovascular disease may want to pay attention to this research, as some of these fermentation products have been associated with these conditions in other studies. Athletes and fitness enthusiasts who consume protein powders regularly might find this relevant. However, this study doesn’t provide enough evidence to make strong recommendations for these groups yet. Healthy people without digestive issues probably don’t need to change their protein choices based on this single study. People with inflammatory bowel disease or other gut conditions should consult their healthcare provider before making changes based on this research.
If you were to switch from a poorly digestible to a highly digestible protein, the changes in blood and urine metabolites would likely appear within days based on this study’s 7-day timeframe. However, whether these changes would produce noticeable health benefits would take much longer to determine, likely weeks to months for any effects on digestion or energy, and years to see impacts on long-term health markers.
Frequently Asked Questions
Does the type of protein powder I drink matter for my health?
Research suggests it may matter for what waste products your gut bacteria create. A 2026 study found that poorly digestible proteins like bovine plasma produce 44% more p-cresyl sulfate in your blood than easily digestible whey protein. However, whether this affects your actual health requires more research.
What is p-cresyl sulfate and why should I care about it?
P-cresyl sulfate is a waste product created when bacteria in your large intestine ferment undigested protein. Some research suggests high levels may be associated with kidney and heart health concerns, though this connection needs more study. This research shows different proteins produce different amounts of it.
Is whey protein better than other proteins for digestion?
This study suggests whey protein isolate produces fewer fermentation metabolites than bovine plasma protein because it’s easier to digest. However, this is one small study, and ‘better’ depends on your individual goals and health status. Consult your doctor for personalized advice.
How long does it take to see differences between protein types?
This study found measurable differences in blood and urine metabolites within 7 days of switching protein sources. However, whether these changes produce noticeable health effects would take much longer, likely weeks to months for digestive changes and years for long-term health impacts.
Should I stop eating poorly digestible proteins based on this research?
Not necessarily. This is a single small study in healthy people. While it shows poorly digestible proteins create more fermentation products, we don’t yet know if this causes health problems for most people. Discuss protein choices with your doctor if you have kidney disease or heart concerns.
Want to Apply This Research?
- Track which protein sources you consume daily and note any changes in digestive symptoms (bloating, gas, constipation, or diarrhea) over 2-4 weeks when switching between easily digestible proteins (whey, casein) and harder-to-digest options (plant-based, bovine plasma).
- If you currently use protein powders, try switching to a whey protein isolate for one week and track how you feel, then switch to a different protein source for comparison. Note any differences in digestion, energy levels, or bloating to see if you personally respond differently to different protein types.
- Create a weekly log comparing protein type consumed with digestive comfort, energy levels, and any other symptoms you notice. Over 4-8 weeks, you’ll develop a personal profile of which protein sources work best for your body, since individual responses may vary from the research findings.
This research is preliminary and based on a small study of 13 healthy adults over 7 days. The findings should not be considered medical advice. Protein choice should be based on your individual health status, dietary needs, and goals. If you have kidney disease, cardiovascular disease, digestive disorders, or other health conditions, consult your healthcare provider or registered dietitian before making changes to your protein intake or protein sources based on this research. This study measured biomarkers but did not demonstrate that these biomarkers cause health problems. Individual responses to different proteins vary significantly.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.
