Researchers followed nearly 40,000 adults in South Korea for over 8 years to see how much soy they ate and whether it affected how long they lived. People who ate more soy products and compounds called isoflavones (which come from soy) had lower chances of dying from any cause during the study period. The benefits seemed to level off at moderate amounts of soy intake, suggesting that some soy is good, but more isn’t necessarily better. This research is particularly relevant for people in countries where soy is a common part of the diet.

The Quick Take

  • What they studied: Whether eating different amounts of soy products and soy compounds affects how long people live and what diseases they develop
  • Who participated: 39,286 Korean adults aged 19 and older who were part of a national health survey between 2007 and 2015
  • Key finding: People who ate moderate to higher amounts of soy had about 25-28% lower risk of dying from any cause compared to those eating very little soy. The benefits appeared strongest at medium intake levels rather than the highest amounts.
  • What it means for you: If you eat soy products, you may be supporting your long-term health. However, this study was done in Korea where soy is very common in the diet, so results may differ in other populations. Talk to your doctor about whether adding soy to your diet makes sense for you personally.

The Research Details

This was a cohort study, which means researchers followed a large group of people over time and tracked what they ate and what happened to their health. The researchers used data from South Korea’s national health survey, which is like a big health checkup program for the country. They asked people what they ate in the previous 24 hours and recorded this information. Then they followed these people for an average of 8.5 years to see who got sick or died and from what causes.

The researchers used a statistical method called Cox proportional hazards models to figure out if eating more soy was connected to living longer. They divided people into five groups based on how much soy they ate—from the lowest amount to the highest amount. Then they compared death rates between these groups to see if there was a pattern.

They also looked at whether the relationship between soy and death was linear (a straight line) or curved (like a hill), which helped them figure out if there’s an ideal amount of soy to eat.

This research approach is important because it follows real people in their everyday lives rather than just testing soy in a lab. By studying a large population in Korea, where soy is eaten regularly, the researchers could see how soy affects people who actually consume it as part of their normal diet. This makes the findings more relevant to understanding soy’s real-world health effects.

This study has several strengths: it included a very large number of people (nearly 40,000), followed them for a long time (8.5 years), and tracked actual deaths rather than just asking people how they felt. However, the study only tracked what people ate once or twice, so we don’t know if their eating habits changed over time. Also, the study was done in Korea, so the results might not apply exactly the same way to people in other countries with different diets and genetics.

What the Results Show

People who ate even small amounts more soy than the lowest group had about 28% lower risk of dying from any cause. This benefit was consistent across the second, third, fourth, and fifth groups—meaning that eating a little more soy helped, but eating much more didn’t help significantly more.

When the researchers looked at specific diseases, they found that soy was particularly helpful for preventing deaths from heart disease and respiratory diseases (like lung problems). For heart disease deaths, people eating medium amounts of soy had the most protection. For respiratory disease deaths, people eating the highest amounts of soy had the best protection—their risk was cut in half compared to those eating the least soy.

For cancer deaths, people eating the most soy had about 23% lower risk compared to those eating the least. The pattern wasn’t as strong as for other diseases, but it still showed a benefit.

Interestingly, the researchers found that the benefits of soy didn’t keep increasing with more and more consumption. Instead, there was a sweet spot—around 9 milligrams of isoflavones per day (the active compound in soy), or about 4 grams of soy protein per day, or about 33 grams of soy foods per day—where the benefits were strongest.

The study also looked at different types of soy intake separately: isoflavones (the plant compounds), soy protein, and whole soy foods. All three showed similar patterns—moderate intake was better than very low intake, but extremely high intake didn’t provide extra benefits. This consistency across different measures of soy consumption strengthens the findings.

Previous research has suggested that soy might be good for heart health and bone health, but most studies were done in Western countries where soy isn’t eaten as much. This study confirms those benefits in a population that eats soy regularly as part of their traditional diet. The finding that moderate amounts are better than very high amounts is new and suggests that soy is beneficial but not in unlimited quantities.

The main limitation is that researchers only asked people what they ate once or twice during the study, so they couldn’t track whether eating habits changed over the 8+ years of follow-up. The study was also done only in Korea, so the results might not apply the same way to people of other ethnicities or in countries where soy is eaten differently. Additionally, the researchers couldn’t prove that soy directly caused the longer lifespan—only that people who ate more soy tended to live longer, which could be due to other healthy habits those people had.

The Bottom Line

If you enjoy soy products, eating moderate amounts (around 30-40 grams of soy foods daily, or about one serving) appears to be associated with health benefits. This could include tofu, tempeh, edamame, soy milk, or miso. You don’t need to eat large amounts—moderate consumption seems to be the sweet spot. Confidence level: Moderate. This is based on a large, well-designed study, but it was done in one country, so results may vary.

This research is most relevant for people of Asian descent or those living in countries where soy is part of the traditional diet. It’s also useful for anyone considering adding soy to their diet for health reasons. People with soy allergies or those taking certain medications that interact with soy should talk to their doctor. Pregnant women and people with hormone-sensitive cancers should also consult their healthcare provider before significantly increasing soy intake.

This study followed people for 8.5 years, so the health benefits of soy appear to develop over months and years, not days or weeks. You shouldn’t expect to feel dramatically different after eating soy for a few days. Instead, think of soy as part of a long-term healthy eating pattern that supports your health over time.

Want to Apply This Research?

  • Track daily soy intake in grams (aim for 30-40g daily) by logging soy foods consumed: tofu servings, soy milk cups, tempeh portions, edamame servings, or miso soup bowls. Record the type and amount to monitor whether you’re hitting the optimal intake range.
  • Set a goal to include one soy-based food at lunch or dinner most days of the week. Start with easy options like adding tofu to stir-fries, drinking soy milk, or snacking on edamame. Track which soy foods you enjoy most to build sustainable habits.
  • Monitor weekly soy intake averages rather than daily amounts, since intake naturally varies. Track alongside other health markers like energy levels and digestion over 2-3 months to see if you notice personal benefits. Use the app to identify patterns between soy consumption weeks and overall wellness scores.

This research suggests an association between soy consumption and lower mortality risk in a Korean population, but it does not prove that soy directly causes longer life. Individual results may vary based on genetics, overall diet, lifestyle, and health conditions. People with soy allergies, those taking blood thinners or hormone-related medications, pregnant women, and those with hormone-sensitive cancers should consult their healthcare provider before significantly changing soy intake. This information is for educational purposes and should not replace personalized medical advice from your doctor.