The shake tastes good. The ingredient list looks clean. You drink it after your workout, same as always. Then, somewhere between changing clothes and heading home, it starts: a low rumble, pressure in your stomach, sometimes worse.
Most people blame the protein. But protein itself is the last thing that causes bloating. The actual mechanism runs deeper, and it explains why plant-based protein sources challenge your digestion more than whey does, and what enzymes have to do with it.
This article breaks down the mechanism from start to finish, evaluates the current research on digestive enzymes, and gives you concrete recommendations. Not promises, but measurable outcomes from the available studies.
Key Takeaways
- Bloating after a protein shake is not caused by protein itself. It is caused by undigested peptides and oligosaccharides that ferment in the colon.
- Pea protein concentrate scores a DIAAS of roughly 64, compared to about 109 for whey isolate. Lower digestibility means more undigested material reaching the colon.1
- Protease supplementation significantly increased postprandial EAA availability from pea protein in a crossover RCT (total plasma amino acids over 5 hours, p = 0.010).4
- Simple adjustments -- keeping portions under 30 g, drinking enough water, sipping slowly -- often reduce GI discomfort without any enzyme supplement.
- DigeZyme contains 5 enzymes (protease, amylase, cellulase, lipase, lactase) involved in digesting all three macronutrient groups.
Contents
Why does protein cause bloating in the first place?
Protein itself does not cause bloating. The culprit is undigested peptides and carbohydrates that bacteria ferment in the colon, producing hydrogen, carbon dioxide, and sometimes methane. A comparative study of 8 protein sources found that the standardized ileal amino acid digestibility of pea protein concentrate was significantly lower than that of whey isolate for nearly every essential amino acid.1
The mechanism has two main channels. First: antinutrients. Legumes like peas and fava beans contain trypsin inhibitors and phytates that bind digestive enzymes and reduce their efficiency. Processing (heat treatment, isolation) reduces these factors substantially in finished protein powders, but it does not eliminate them entirely.
Second: oligosaccharides. Peas contain raffinose and stachyose, sugar chains that the human small intestine cannot break down. They pass intact into the colon and become a rich substrate for bacterial fermentation. The process runs faster than with whey because, simply put, more undigested material arrives.
None of this is an argument against plant protein. It is an argument for understanding the difference and responding accordingly.
Mathai et al. compared 8 protein sources using DIAAS (Digestible Indispensable Amino Acid Score) and standardized ileal amino acid digestibility in a porcine model. Pea protein concentrate scored a DIAAS of ~64; whey isolate scored ~109. Digestibility of essential amino acids -- particularly methionine and lysine -- was significantly lower for pea protein across nearly all EAAs. The authors also demonstrated that the PDCAAS system systematically overestimates the quality of plant proteins.1
A lower DIAAS translates directly: a larger fraction of peptides reaches the colon before being fully absorbed. That is exactly where fermentation begins.
Pea protein concentrate scores a DIAAS of roughly 64, versus roughly 109 for whey isolate. The gap is driven primarily by lower ileal digestibility of essential amino acids such as methionine and lysine. The more undigested peptides that reach the colon, the higher the fermentation potential. (Mathai et al., British Journal of Nutrition, 20171)
Plant protein and digestion -- what is different from whey?
Whey protein is highly soluble and absorbed quickly and almost completely in the small intestine. Van der Heijden et al. compared six plant protein sources in 2024 and found that pea protein had the highest EAA availability among the tested plant proteins, but individual variability between subjects was substantial and the gap to whey remained significant.2
Two factors account for most of the difference:
Solubility and gastric emptying. Whey reaches the small intestine faster, where the bulk of absorption occurs. Plant proteins, especially in their native structure, have a more compact protein matrix that takes longer to break down.
Physical processing. How aggressively a plant protein is processed changes its digestibility dramatically. West et al. (2024) showed that in the gastric phase, in-vitro protein availability from highly extruded plant protein was roughly 590 mg/mL, compared to over 2,150 mg/mL for less processed material. That is a 1:4 ratio, measured before the small intestine even gets involved.3
Van der Heijden et al. tested 6 plant protein sources (pea, mycoprotein, spirulina, chlorella, lupin, and one more) in 22 participants each (young and older adults). Pea protein yielded the highest postprandial plasma EAA availability of the group. Differences between sources were statistically significant (p < 0.001). Between-subject variability was large, underscoring the difficulty of one-size-fits-all recommendations.2
Worth noting: plant protein is not inherently hard to digest. With adequate total daily intake and a combination of pea and fava bean protein, the amino acid gaps of individual sources can be closed. Our article on pea protein and fava bean protein explains in detail why this works and how the combination addresses the methionine limitation.
In a head-to-head comparison of six plant protein sources, pea protein delivered the highest postprandial EAA availability. Yet individual differences between subjects were larger than the differences between protein sources -- no one-size-fits-all. (Van der Heijden et al., British Journal of Nutrition, 20242)
How digestive enzymes address the problem -- the mechanism behind DigeZyme
Digestive enzymes intervene where the problem originates: in the stomach and small intestine, before peptides reach the colon. A double-blind, placebo-controlled crossover RCT with 24 participants (Paulussen et al., 2024) showed that a microbial protease blend co-ingested with 25 g pea protein significantly increased total plasma amino acids over 5 hours versus placebo (p = 0.010), with especially strong effects on EAA, BCAA, and leucine in the early postprandial phase (0-2 h, all p < 0.05).4
What do the individual enzymes actually do?
Protease cleaves protein molecules into shorter peptide chains and amino acids. Fewer peptides in the colon means less substrate for fermentation. It does not get more direct than that.
Amylase breaks down starch and carbohydrates, including polysaccharides from the legume matrix that can physically encase protein molecules.
Cellulase is the uncommon one: it breaks down plant cell walls. Humans do not produce cellulase endogenously. For plant protein derived from legume cell structures, this matters. It opens up the protein matrix for better breakdown.
Lipase handles fat digestion, relevant because many people mix their shakes with milk or milk alternatives. Lactase covers lactose -- useful when mixing with cow's milk.
Paulussen et al. tested a microbial protease blend (P3) with 25 g pea protein in 24 healthy adults (27 ± 4 y). Result: total plasma amino acids significantly higher over 0-5 h (p = 0.010), EAA, BCAA, and leucine in the 0-2 h phase all p < 0.05 vs. placebo. Independent research group (University of Illinois).4
Huang et al. replicated the design using 24 g whey protein instead of pea. The same protease blend increased EAA by 14 % and BCAA by 15 % in iAUC over 60 minutes (both p < 0.025). Ghrelin dropped 12 % lower (p < 0.001). The takeaway: enzymes do not only improve digestion of plant proteins.5
Here it pays to stay differentiated. Deutz et al. (2026) tested a 6-enzyme complex with a mixed meal in 30 middle-aged and older adults. Leucine reached its plasma peak 20 minutes earlier with the enzyme supplement (p = 0.047). But for total amino acids, there was no statistically significant group difference -- the benefit varied considerably by BMI, body composition, and habitual macronutrient intake.6
This is the point that most marketing messages miss: enzymes help, but not equally for everyone, not at every dose, and not measurably in every study design. Rathi et al. (2024) found statistically significant improvements for only two out of many amino acids in a pilot study (n = 15) using an enzyme-probiotic complex with pea protein.7
The reframe: the mechanism is biologically plausible and supported by solid independent RCTs. The people most likely to benefit are those consuming larger portions of plant protein, those with lower individual digestive efficiency, or those with GI sensitivity.
DigeZyme contains enzymes (protease, amylase, cellulase, lipase, lactase) involved in digesting all three macronutrient groups. There are no EFSA-approved health claims for enzyme complexes -- the evidence comes from independent RCTs, not product promises.
For completeness: the only human RCT specifically investigating the DigeZyme complex was conducted by Majeed et al. (2018). 40 patients with functional dyspepsia received 50 mg DigeZyme three times daily for 60 days; all five dyspepsia scores improved significantly versus placebo.8 The key caveat: the lead author and co-authors are founders and employees of Sabinsa Corporation, the manufacturer of DigeZyme. And: functional dyspepsia patients are not healthy athletes. Whether these results transfer to a normal shake context is unproven. The findings are plausible, but the conflict of interest must be factored into any interpretation.
Microbial protease supplementation increased EAA availability from whey protein by 14 % and BCAA by 15 % (iAUC 60 min, both p < 0.025) in a double-blind crossover RCT. The effect is not limited to plant protein. (Huang et al., Journal of Nutrition, 20255)
What you can do: dosing, timing, and hydration
Bloating after a shake is often not about protein quality but about portion size. You can improve protein powder digestion through simple adjustments long before enzyme supplements become necessary. The small intestine has a limited absorption capacity per unit of time -- single servings above 30-40 g of protein increase the amount of undigested peptides reaching the colon. Schoenfeld and Aragon recommend 0.4 g protein per kg body weight per meal as a practical guideline in their widely cited review (2018).9
Here are the five most effective adjustments:
1. Portion size. Aim for 25-30 g protein per shake instead of 40 g. At 80 kg body weight and 0.4 g/kg, that is 32 g. In practice, 25-28 g works for most people without crossing the bloating threshold.
2. Hydration. Use at least 250-300 mL of water per serving. Concentrated shakes with too little liquid slow gastric emptying. More water means thinner consistency and faster passage into the small intestine.
3. Drinking speed. Sip slowly instead of downing the shake in two gulps. Fast drinking pulls air into the stomach -- a standalone bloating factor that has nothing to do with protein.
4. Gradual introduction. If you are new to plant protein powder or restarting after a break, begin with half a serving during the first week. Your gut microbiome needs time to adapt to the new substrate.
5. Digestive enzymes. If available, take them at the same time as your shake -- not 30 minutes later. Enzymes need to be present in the stomach alongside the protein to work.
The optimal protein amount per meal is roughly 0.4 g/kg body weight, according to Schoenfeld & Aragon (2018). For a 75 kg person, that is about 30 g protein per shake. Larger single servings increase the amount of undigested peptides reaching the colon and, with it, fermentation potential. (Journal of the International Society of Sports Nutrition, 20189)
One thing many people overlook: temperature matters. Cold shakes marginally slow enzymatic activity in the stomach, but shakes made with very hot liquid denature any added enzymes. Room temperature or cold is optimal.
And one more thing: if you have been dealing with significant bloating every day for weeks, it is worth talking to a doctor. Lactose intolerance, irritable bowel syndrome, or sensitivity to certain carbohydrates (FODMAPs) can be independent causes that are only tangentially related to protein powder.
FAQ: Common questions about protein shakes and digestion
Whey protein is highly soluble and absorbed quickly and almost completely in the small intestine -- very little reaches the colon. Plant protein from peas has a lower ileal digestibility (DIAAS ~64 vs. ~109 for whey). This means a larger fraction of peptides and oligosaccharides from legumes reaches the colon, where bacteria ferment them.
On top of that, peas and fava beans contain oligosaccharides like raffinose and stachyose that the small intestine simply cannot break down -- humans do not produce the alpha-galactosidase enzyme needed for that. These sugars are a direct fermentation substrate. In well-processed protein powder (isolated, heat-treated), these compounds are reduced but not eliminated.
Research shows that protease supplementation significantly improves postprandial amino acid availability from pea protein (Paulussen et al., 2024). More amino acids absorbed in the small intestine means fewer peptides for colon fermentation -- logically, that means less gas production.
However, there is no large-scale RCT that measures bloating as a primary endpoint while specifically testing sports-nutrition enzyme complexes in healthy athletes. The best available DigeZyme study was conducted in patients with functional dyspepsia, by researchers with a conflict of interest. The principle is well supported; the specific claim "DigeZyme reduces bloating" is not scientifically validated for healthy individuals.
Practical take: digestive enzymes are a useful tool, not a silver bullet. Optimizing portion size and hydration often does as much or more than any supplement.
Most people report noticeably better tolerance after 2 to 4 weeks of regular use. The mechanism: your gut microbiome adapts to the new substrate and shifts its composition. Bacterial strains that aggressively ferment oligosaccharides become less dominant or relocate to different sections of the gut with sustained exposure.
Starting with half a serving during the first week speeds up this adaptation and significantly reduces initial discomfort. If you still experience strong symptoms after four weeks at normal dosing, it is worth considering other causes (IBS, FODMAP intolerance).
The role of digestive enzymes in protein powder -- and why DigeZyme covers all five enzyme classes -- is explored in greater depth in our dedicated article on digestive enzymes in protein powder.
The Bottom Line
Bloating after a protein shake is a solvable problem. The mechanism is well understood: undigested peptides and oligosaccharides from plant protein ferment in the colon because pea protein is structurally less digestible than whey. Digestive enzymes can improve this process -- independent RCTs show that clearly. But the biggest difference often comes from the simplest adjustments: keeping portions under 30 g, drinking enough water, sipping slowly, and easing in during the first week.
References
- Mathai, J. K., Liu, Y. & Stein, H. H. (2017). Values for digestible indispensable amino acid scores (DIAAS) for some dairy and plant proteins may better describe protein quality than values calculated using the concept for protein digestibility-corrected amino acid scores (PDCAAS). British Journal of Nutrition, 117(4), 490-499. doi:10.1017/S0007114517000125 (PMID: 28382889)
- van der Heijden, I. et al. (2024). The effect of dietary protein source on postprandial plasma amino acid availability across the adult lifespan. British Journal of Nutrition, 132(1), 1-14. doi:10.1017/S0007114524000163 (PMID: 38220222)
- West, S. et al. (2024). Processing method affects postprandial plasma amino acid availability from plant-based proteins. Journal of Nutrition, 154(7), 2145-2157. doi:10.1016/j.tjnut.2024.05.018 (PMID: 38797481)
- Paulussen, K. J. M. et al. (2024). A microbial protease mixture increases postprandial essential amino acid availability of a plant-based protein blend in healthy young adults. Journal of Nutrition, 154(5), 1572-1583. doi:10.1016/j.tjnut.2024.03.009 (PMID: 38467279)
- Huang, J. et al. (2025). Microbial protease supplementation improves early postprandial amino acid bioavailability and attenuates appetite from whey protein in healthy adults. Journal of Nutrition, 155(9), 2589-2600. doi:10.1016/j.tjnut.2025.07.006 (PMID: 40675336)
- Deutz, N. E. P. et al. (2026). A multi-enzyme supplement accelerates leucine appearance but does not increase overall postprandial plasma amino acid availability in healthy middle-aged and older adults. Journal of Nutrition, online ahead of print. doi:10.1016/j.tjnut.2026.101400 (PMID: 41662956)
- Rathi, P. et al. (2024). Pea protein with enzyme-probiotic blend: a pilot randomized crossover study on amino acid availability and gut microbiome. Frontiers in Nutrition, 11, 1307734. doi:10.3389/fnut.2024.1307734 (PMID: 38321993)
- Majeed, M. et al. (2018). A pilot, randomized, double-blind, placebo-controlled trial to assess the safety and efficacy of a novel Digest-Ease formulation in subjects with functional dyspepsia. Journal of Medicinal Food, 21(11), 1120-1128. doi:10.1089/jmf.2017.4172 (PMID: 30156436) Conflict of interest: lead author and co-authors affiliated with Sabinsa Corporation (manufacturer of DigeZyme).
- Schoenfeld, B. J. & Aragon, A. A. (2018). How much protein can the body use in a single meal for muscle-building? Implications for daily protein distribution. Journal of the International Society of Sports Nutrition, 15, 10. doi:10.1186/s12970-018-0215-1 (PMID: 29497353)
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