Research shows that protein digestibility depends on both the food and the person eating it. A 2026 laboratory study found that the widely used pH-stat method overestimated plant protein digestion by up to 92% compared with LC-MS, a precise measurement tool. Digestion dropped to 30 to 60% in simulated older-adult conditions.
According to research reviewed by Gram, how well your body can use protein depends on more than how much protein a food contains. In this 2026 laboratory study, scientists used a model that mimics human digestion to compare six animal and plant proteins across three simulated body types: adult men, adult women, and adults aged 70 and older. The team tested four measurement methods and found that one common method, the pH-stat test, overestimated plant protein digestibility. It gave soy a reading of 124.8%, while the more precise LC-MS method measured 64.9%. Digestion appeared to slow considerably under simulated older-adult conditions, dropping to 30 to 60%. Simulated female digestion also released more essential amino acids from oat protein. Because this work was done in a lab rather than in people, it mainly improves how protein quality is tested and does not yet show exactly what happens in a real body.
Key Statistics
A 2026 laboratory study published in Food Research International found that the pH-stat method gave soy protein a digestibility reading of 124.8%, compared with 64.9% measured by the more precise LC-MS method.
A 2026 in vitro study of six animal and plant proteins found that protein digestion fell to between 30% and 60% under simulated senior digestive conditions.
The 2026 study compared digestion across three simulated profiles, including adult males, adult females, and adults aged 70 and older, using four different measurement methods.
The Quick Take
- What they studied: The researchers wanted to know how easily the body breaks down and absorbs protein from different foods, and whether that changes with sex and age. They also wanted to find out which lab methods give the most accurate answer.
- Who participated: No people took part in this study. Instead, the researchers used lab models that copy human digestion. They tested six protein sources, including animal and plant foods, under three simulated conditions: adult male, adult female, and senior (age 70 and older). The study did not report a participant count.
- Key finding: The most accurate lab method, LC-MS, showed that digestion of protein from plant foods was much lower than a common cheaper test suggested. For example, soy protein read 124.8% with the pH-stat test but 64.9% with LC-MS. Under simulated senior digestion, protein breakdown fell to between 30% and 60%.
- What it means for you: Plant proteins may be less fully digested than some test numbers suggest, and older adults may get less usable protein from the same food. These findings come from lab work, so they are best used to guide food science research. They do not yet tell you how much protein to eat or which foods to choose.
The Research Details
This was an in vitro study, which means it was carried out in a lab rather than in living people. The researchers built a multi-step model that copies the stomach and intestines by using acids, enzymes, and bile salts to break down food. They changed these conditions to match three profiles: an adult male, an adult female, and an older adult aged 70 or more. This let them see how digestion might differ for each group.
The team tested six protein sources, mixing animal and plant foods such as soy and oat. They measured how much protein broke down using four different methods. Two were chemical tests that track changes in acidity or reactive groups, one used a color-based test, and the last used a precise instrument called liquid chromatography-mass spectrometry, or LC-MS, which counts individual amino acids. The researchers then compared each method’s results to see which gave the most reliable answers.
The team also calculated a score called the digestible indispensable amino acid ratio, or DIAAR. This score shows how well a food supplies the essential building blocks of protein that the body cannot make on its own. Comparing these scores across methods and body profiles helped the authors judge where lab tests can go wrong.
Protein quality scores are used to label foods and guide nutrition advice, so the measuring tools behind those scores need to be accurate. By testing several methods side by side, this study showed that some common tests can overstate how much plant protein the body can use. Testing across different simulated body types also shows that a single number may not fit everyone.
The study compared several measurement methods against each other, which is a strength because it reveals where individual tests disagree. It used a precise instrument, LC-MS, as a reference point. However, lab models cannot fully reproduce the living human gut, which includes gut bacteria, immune responses, and differences between individuals. The paper also did not report how many separate tests were run for each condition, so the consistency of the results is harder to judge. Findings should be treated as early evidence that needs confirmation in people.
What the Results Show
For animal proteins, the different lab methods gave closely matching results. This suggests that animal protein digestion is easier to measure reliably with standard tools.
Plant proteins told a different story. The pH-stat method overestimated how well plant proteins were digested, with results running up to 92% higher than the LC-MS values. The researchers suggested that substances other than protein, such as soluble fibers, phytic acid, and polyphenols, may interfere with the test and make plant protein look more digestible than it is. For soy, the pH-stat reading was 124.8%, compared with 64.9% from LC-MS. A reading above 100% is not possible for true digestion, which signals that the test was picking up something other than protein breakdown.
The study also found that the OPA color-based test overestimated results under simulated senior digestive conditions. The authors suggested this may come from the breakdown of the food and gut material itself, along with nitrogen from non-protein sources. LC-MS, by contrast, tracked amino acids directly in the digestive fluid and showed a clear drop in digestion for older adults, to between 30% and 60%.
Sex-based differences also appeared. Simulated female digestive conditions released significantly more essential amino acids from oat proteins, and most other plant proteins showed a similar upward trend. The authors concluded that protein quality depends on both the food and the body it enters.
The authors suggested that OPA and LC-MS are useful tools for avoiding measurement bias, meaning that they give more trustworthy results than the pH-stat test for plant foods. This matters for food companies and researchers who label or compare protein quality. The senior-condition results also point to a practical concern: older adults may get less usable protein from the same food, which may matter for muscle maintenance. Because these are lab findings, they highlight questions to test in future human studies rather than offering final answers.
Earlier work has shown that plant proteins often score lower than animal proteins on protein quality measures, and that fiber and other food components can affect how well protein is absorbed. This study adds evidence that some lab tests can exaggerate plant protein digestibility and that age and sex may change digestion in the lab model. It supports the broader view that a single protein score may not capture how the body handles different foods.
This study was done in a lab model, not in people, so it cannot show exactly how much protein a real person absorbs from a meal. Lab models simplify digestion and do not include gut bacteria, hormones, or differences in health between individuals. The study did not report how many repeated tests were run, which makes it harder to judge how consistent the results are. The simulated senior and female conditions are based on general patterns, not on a group of real people. The authors also note that some lab methods are affected by non-protein substances in food, which means the choice of method strongly shapes the answer.
The Bottom Line
Based on this lab evidence, food researchers and labs may want to avoid relying on the pH-stat method alone when testing plant proteins, and to use LC-MS or the OPA method for more reliable results. Confidence in this recommendation is moderate, since it comes from a single laboratory study. Consumers should not change their diets based only on this research. People who eat mostly plant proteins may still benefit from varied foods and enough total protein, as supported by broader nutrition guidance.
Food scientists, nutrition researchers, and food labelers will find these results most relevant because they affect how protein quality is measured. Adults aged 70 and older, and those who rely heavily on plant proteins, may find the age-related findings worth discussing with a healthcare provider or registered dietitian. People without specific concerns about protein intake do not need to change their habits based on this study alone.
Changes in lab testing practices can take months to years as researchers compare methods and update standards. For individuals, this research does not offer a short-term change to expect. Any real-world effects on protein intake or muscle health would need to be confirmed in human studies, which typically take months to years to complete.
Frequently Asked Questions
Does the body digest plant protein as well as animal protein?
A 2026 lab study suggests plant protein may be digested less completely than some common tests indicate. Using the precise LC-MS method, soy protein measured 64.9%, while the pH-stat test gave 124.8%. Results come from lab models, not people.
Do older adults digest protein less efficiently?
Lab simulations of senior digestion showed protein breakdown falling to between 30% and 60%. The study suggests older digestive conditions may limit how much protein the body can use. Researchers say human studies are needed to confirm these effects in real people.
Which method is most accurate for measuring protein digestibility?
According to research reviewed by Gram, the LC-MS method was the most reliable in this study because it directly measures individual amino acids. The pH-stat method overestimated plant protein digestion, likely due to fiber, phytic acid, and polyphenols interfering with the test.
Does biological sex affect how protein is digested?
In this lab study, simulated female digestive conditions released significantly more essential amino acids from oat protein than male conditions did. Other plant proteins showed similar upward trends. These findings come from lab models and are not yet confirmed in human participants.
Want to Apply This Research?
- Track daily protein intake in grams and note the main protein sources at each meal, such as soy, oats, dairy, or meat. Aim to log at least 5 days per week so you can see patterns over time. Record your total protein for the day and the share that comes from plant foods.
- Encourage users to include a variety of protein sources across meals, such as combining legumes with grains, and to check that each day includes some animal or complementary plant proteins. Suggest that users who are 70 or older talk with a healthcare provider about their protein needs before making major changes.
- Over several months, review weekly protein totals and the balance between plant and animal sources. For users in older age groups, consider adding notes on energy levels, appetite, and any changes in strength or weight, and share these trends with a clinician during regular checkups.
This article summarizes a laboratory study that used models of human digestion rather than testing people directly. Results may not apply to how individuals digest food in real life. This content is for general information only and is not medical or nutritional advice. Please consult a doctor or registered dietitian before making changes to your diet, especially if you are older, have a health condition, or follow a restricted diet.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.