Pooled Study of Half a Million People Clears Soy of Bladder Cancer Link, but Raises Questions About Soybean Oil

A new study published in the journal Nutrients on 22 September 2026 has found that eating soy in general is not linked to a higher or lower risk of bladder cancer. However, the researchers did notice that people who consume soybean oil had higher rates of the disease — a finding the authors themselves describe as preliminary and in need of further research.

A large study across three continents

The study was carried out by a team from the School of Public Health at Southeast University in Nanjing, China, together with Maastricht University in the Netherlands. The researchers pooled data from 12 long-term studies in 10 countries across Europe, Asia and the Americas, covering 549,458 people. Participants were followed for years, and 3,164 of them developed bladder cancer during that time — fewer than 6 in every 1,000.

What did the researchers find?

• Soy overall: No link between how much soy a person eats and their risk of bladder cancer.
• Soybeans, soy milk and soy paste: No clear link.
• Soybean oil: People who consumed it had a roughly 50% higher risk than those who did not, rising to between about 50% and 70% at moderate and high intake.
• Men and women differ: In men, the link with soybean oil was clearer. In women who ate moderate amounts of soybeans, the risk was about half that of women who ate none.

Why soybean oil?

Soybean oil is rich in linoleic acid, an omega-6 fatty acid. This acid oxidises easily when cooked at high temperatures or when oil is reheated several times, producing compounds that may be harmful.

But the researchers offered another explanation that is just as important: soybean oil may simply be a marker of an overall diet heavy in fried and processed foods, rather than the cause itself. They also noted that soybean oil contains almost none of the isoflavones found in soybeans — the compounds thought to have a protective role against cancer.

No cause for alarm — here's why

The researchers stressed that the results show an association, not proven cause and effect, and pointed to several reasons for caution:

• The study did not account for important factors such as body weight, physical activity, income level and chemical exposure at work.
• It also did not include well-known risk factors such as arsenic in drinking water and schistosomiasis (bilharzia) infection.
• More than 99% of participants were of European descent with very low soy intake, so the results may not apply to other populations.
• Diet was recorded only once, at the start of the study, while eating habits change over the years.
• The separate results for men and women rest on a relatively small number of cases.

The main causes are well known

Smoking remains the biggest risk factor for bladder cancer, along with exposure to arsenic in drinking water and bilharzia infection. Bladder cancer is one of the most common cancers worldwide, and about 75% of cases occur in men.

The bottom line

According to this study, soy as a food is not to blame. Soybean oil needs more precise research that looks at cooking methods, how often oil is reheated and the whole diet. Until then, the general advice stands: cut back on deep frying, don't reuse cooking oil, and vary the sources of fat in your diet.

Source: Nutrients, Vol. 18, Issue 19, 2026