Habitual soy food intake is linked to healthier kidneys in people with type 2 diabetes. In a 2026 cross-sectional study of 4,922 Japanese adults, Gram Research analysis found that frequent natto eaters had about half the odds of reduced kidney filtration (adjusted odds ratio 0.49) compared with those who ate it least.
According to research reviewed by Gram, Japanese adults with type 2 diabetes who often ate soy foods were less likely to have signs of weakened kidneys. Researchers in the Fukuoka Diabetes Registry studied 4,922 people and asked about their eating habits with a diet questionnaire. People who frequently ate natto, a fermented soybean dish, miso soup, or tofu had lower rates of reduced kidney filtering. Natto eaters also showed fewer signs of protein leaking into their urine, an early warning sign of kidney damage. Higher intake of isoflavones, natural plant compounds found in soy, was linked to lower odds of both problems. Because the study looked at a single snapshot in time, it cannot prove that soy protects the kidneys. Still, the results suggest that regularly eating soy foods may be a helpful part of a diabetes-friendly diet.
Key Statistics
A 2026 cross-sectional study of 4,922 Japanese adults with type 2 diabetes found that people who ate natto most often had 49% lower odds of reduced kidney filtration than those who ate it least.
In the same 2026 Fukuoka Diabetes Registry analysis, frequent miso soup drinkers had 37% lower odds of reduced kidney filtration, and frequent tofu eaters had 48% lower odds compared with the lowest eating groups.
The Quick Take
- What they studied: Researchers wanted to know whether eating soy foods, such as natto, miso soup, and tofu, is linked to better kidney health in people with type 2 diabetes. They also looked at isoflavones, plant compounds found in soy.
- Who participated: The study enrolled 4,922 adults in Japan who had type 2 diabetes. They were part of the Fukuoka Diabetes Registry, a long-running database that tracks people with diabetes in the Fukuoka area.
- Key finding: People who ate natto most often had about half the odds of reduced kidney filtration compared with those who ate it least (odds ratio 0.49, meaning roughly 51% lower odds). Frequent miso soup and tofu eaters also had lower odds, at 0.63 and 0.52.
- What it means for you: If you have type 2 diabetes, adding soy foods like natto, tofu, or miso soup to your regular meals may be associated with better kidney health. This study cannot prove soy causes the difference, so it should be viewed as one supportive piece of a broader plan that your doctor helps you manage.
The Research Details
This was a cross-sectional study, which means researchers took a snapshot of people at one point in time rather than following them over many years. Each participant completed a self-administered diet history questionnaire, a form that asks how often they eat various foods over a set period. This allowed the team to estimate how much soy, including natto, miso soup, tofu, and isoflavones, each person usually consumed.
Kidney health was measured in two main ways. The first was estimated glomerular filtration rate (eGFR), a number that shows how well the kidneys filter waste from the blood. The team calculated it using a blood marker called cystatin C. The second was albuminuria, which means protein leaking into the urine. It was defined as a urinary albumin-to-creatinine ratio of 30 mg/g or higher, a common sign of early kidney stress.
To compare groups, the researchers used a statistical method called logistic regression. It estimates the odds that a person has a kidney problem based on their soy intake, while adjusting for other factors that could affect results, such as age, blood sugar control, and body weight.
Snapshot studies like this one are useful for spotting patterns across large groups of people. Because the study included nearly 5,000 participants, it can show whether eating habits and kidney health tend to appear together. Adjusting for other factors also helps separate the effect of soy from things like age or weight, which can influence kidney health on their own.
The approach has a clear limit, though. Since everything was measured at the same time, the study cannot show which came first or prove that soy directly protects the kidneys. It can only show that the two are connected. Long-term studies and controlled trials would be needed to test whether changing soy intake actually changes kidney outcomes.
The study used a large group of participants, which strengthens confidence that the patterns are real rather than due to chance. The statistical results include 95% confidence intervals, which show the range the true value likely falls within. For natto, that range was 0.37 to 0.65, which is fairly narrow and suggests a consistent pattern.
Several factors limit how much weight to place on the results. Diet questionnaires rely on memory and can be inaccurate. The design cannot prove cause and effect. The study also focused on people in one region of Japan who already had type 2 diabetes, so results may not apply to everyone. Note that the abstract reports 4,922 enrolled participants, while the sample size listed for this summary is 922. Readers who want the exact number analyzed should check the full paper.
What the Results Show
The clearest finding involved kidney filtration. Participants who frequently ate natto had about half the odds of having reduced kidney filtration compared with those who ate it least. The adjusted odds ratio was 0.49, meaning the odds were roughly 51% lower in the highest eating group. This was the strongest association in the study.
Frequent miso soup and tofu consumption also showed lower odds of reduced kidney filtration. For miso soup, the odds ratio was 0.63, and for tofu it was 0.52. Taken together, these results suggest that the people who ate soy foods most often were less likely to have weaker kidney filtering, even after accounting for many other differences between them.
The picture was more mixed for protein in the urine. Only frequent natto consumption was inversely associated with albuminuria. Miso soup and tofu did not show the same link for this measure. Higher isoflavone intake, however, was associated with lower odds of both reduced kidney filtration and albuminuria.
Isoflavones appeared to matter for both kidney measures, which is notable because it points to a possible mechanism. Isoflavones are plant compounds that act somewhat like weak plant-based estrogens in the body and have antioxidant properties. Researchers often study them for heart and bone health, and this study adds a possible kidney connection. Still, the study did not measure how isoflavones act inside the body, so this remains a hypothesis.
The fact that natto showed the strongest links across both kidney measures is also worth noting. Natto is a fermented food, and fermentation can change how soy proteins and compounds are absorbed. This may help explain why it stood out, though the study was not designed to test this idea.
Earlier research on soy and kidney health has been limited, which the authors themselves note. Many studies on soy have focused on heart disease, cholesterol, or bone health. This study adds to a smaller body of work examining soy specifically in people with diabetic kidney disease. Its large sample from a Japanese population, where soy is a traditional staple, makes it a useful addition. Because the evidence is still developing, these findings should be seen as a promising lead rather than a settled conclusion.
The most important limitation is that this was a snapshot study. It shows that soy eating and better kidney health tend to occur together, but it cannot prove that soy causes better kidney function. People who eat more soy may also differ in other ways, such as overall diet quality, activity level, or healthcare habits, even though the researchers adjusted for many factors.
Diet was measured using a self-reported questionnaire, which depends on people remembering and estimating what they ate. These estimates can be off, which could weaken the results. The study also included only people in one region of Japan who already had type 2 diabetes, so the findings may not apply to other populations, to people without diabetes, or to people eating very different diets.
Finally, the results for miso soup and tofu were not consistent across both kidney measures, so they should be interpreted with more caution than the natto findings.
The Bottom Line
Based on this study, eating soy foods regularly may be a reasonable, low-risk habit for people with type 2 diabetes who want to support kidney health. The evidence is moderate at best. It comes from one cross-sectional study, so confidence is higher that the pattern exists than that soy is the cause. Natto showed the most consistent results, followed by tofu and miso soup. People should continue following any kidney and diabetes treatment plan their doctor recommends, since diet alone cannot replace medical care.
People with type 2 diabetes, especially those who already eat Japanese-style foods or who are looking for diet changes to support kidney health, may find these results useful. Dietitians and healthcare providers who counsel diabetes patients may also want to know about this research.
People with kidney disease who need to limit potassium or phosphorus should check with their care team first, since soy foods contain these minerals. People with soy allergies, or those taking medications that interact with diet, should also speak with a doctor before making changes. People without diabetes can still eat soy as part of a healthy diet, but this study does not directly address their kidney health.
This study cannot show how long it takes for soy intake to affect kidney health. Kidney changes in diabetes usually develop slowly over years, so any benefit from dietary changes would likely be gradual and measured over months to years, not weeks. Readers should not expect quick or noticeable changes in how they feel. Kidney function is typically tracked with regular blood and urine tests, which a doctor can order to monitor progress.
Frequently Asked Questions
Does eating soy help protect kidneys in people with diabetes?
A 2026 study of 4,922 Japanese adults with type 2 diabetes linked frequent soy eating to better kidney filtration. The link was strongest for natto, where the highest eaters had 49% lower odds of reduced filtration. Because the study was a single snapshot, it cannot prove soy caused the difference.
What is natto and why is it linked to kidney health?
Natto is a fermented soybean dish popular in Japan. In this study, frequent natto eaters showed the strongest associations with both better kidney filtration and less protein in the urine. Fermentation may influence how soy compounds are absorbed, but the study did not test this directly.
What are isoflavones and do they help the kidneys?
Isoflavones are plant compounds found mainly in soy foods. In this study, higher isoflavone intake was associated with lower odds of both reduced kidney filtration and albuminuria, which is protein leaking into the urine. These are observational associations, so they do not prove isoflavones protect the kidneys.
Should people with diabetes eat more tofu or miso to protect their kidneys?
Frequent tofu and miso soup eaters had 48% and 37% lower odds of reduced kidney filtration, respectively, in this study. Those links did not appear consistently for protein in urine. Anyone with kidney disease should check with their doctor before changing their diet, since soy contains potassium and phosphorus.
Want to Apply This Research?
- Log the number of servings of soy foods you eat each week, counting natto, tofu, miso soup, soy milk, and edamame separately. Aim to track at least 4 weeks to see your typical pattern. Record a weekly count, such as 3 servings of tofu and 2 servings of natto, so you can compare your intake over time.
- Try adding one soy food to a meal you already eat several times a week. For example, add tofu to a stir-fry, swap a snack for edamame, or have miso soup with lunch. Set a simple goal, such as eating soy at least three times per week, and mark each day you meet it in the app. If natto is not to your taste, start with tofu or miso and try natto later.
- Review your soy intake log monthly and pair it with your regular diabetes and kidney check-ups. Ask your doctor to track eGFR and urine albumin tests, and bring the results to your monthly review so you can see whether changes in diet align with lab values over time. Update your goals every three months, and share your log with your care team so they can advise on any dietary adjustments.
This article summarizes a cross-sectional study, which shows associations between soy intake and kidney health at one point in time but cannot prove cause and effect. It is for general information only and is not medical advice. Anyone with type 2 diabetes or kidney concerns should talk with a doctor, registered dietitian, or kidney specialist before changing their diet, especially if they have kidney disease, take medications, or have soy allergies.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.