Low-carb, animal fat/protein-heavy diet poses increased bladder cancer risk

A low-carbohydrate diet (LCD), particularly when its fat and protein sources are predominantly animal-based, may contribute to increased risk of bladder cancer among Chinese Singaporeans, according to new research.

Analysis of large data from the Singapore Chinese Health Study showed that compared with participants in the lowest quartile of animal-based LCD score, those in the second, third, and fourth quartiles had bladder cancer risk that was higher by 9 percent (hazard ratio [HR], 1.09, 95 percent confidence interval [CI], 0.76–1.56), 17 percent (HR, 1.17, 95 percent CI, 0.81–1.70), and 53 percent (HR, 1.53, 95 percent CI, 1.09–2.17), respectively (p=0.01 for trend). [BJUI Compass 2025;6:e70033]

Each standard deviation-increase in the animal-based LCD score corresponded to a 16-percent higher risk (HR, 1.16, 95 percent CI, 1.02–1.32; p=0.01 or trend).

Conversely, there was no association observed between plant-based LCD score and the risk of bladder cancer (per SD increment: HR, 1.08, 95 percent CI, 0.91–1.28; p=0.78 for trend).

“To our knowledge, the current analysis was the first study evaluating the association between LCD scores and risk of bladder cancer in the Chinese population,” the authors said.

The findings stand in contrast with data from the Japan Public Health Center (JPHC)-based Prospective Study Group, which involved 90,171 Japanese and 247 incident cases of bladder cancer with a median follow-up of 17.0 years. In the JPHC cohort, total LCD (Q5 vs Q1: HR, 1.00, 95 percent CI, 0.72–1.39; p=0.81 for trend), animal-based LCD (Q5 vs Q1: HR, 1.03, 95 percent CI, 0.75–1.41; p=0.81 for trend), and plant-based-LCD (Q5 vs Q1: HR, 0.78, 95 percent CI, 0.58–1.07; p=0.15 for trend) scores showed null associations with the risk of bladder cancer.

“The discrepancy between our results and those in the JPHC cohort study might be due to differences in dietary patterns and lifestyle characteristics between Chinese Singaporeans and the Japanese population. For instance, the Chinese Singaporeans have higher consumption of animal protein (mean intake [Q5], 45 g/day) and carbohydrate (mean intake [Q1], 250 g/day) than those in the Japanese population (animal protein: mean intake [Q5], 11.3 g/day; carbohydrate: mean intake [Q1], 66 g/day),” the authors explained. [Cancer Sci 2022;113:744-755]

How animal-based LCD contributes to the risk-increase for bladder cancer may be related to a diet with high protein and fat from animal sources, but low total carbohydrate. The authors noted that such is especially true for high intake of processed meat, considering that cooking and/or processing meats generate carcinogens such as heterocyclic amines (HCAs), polycyclic aromatic hydrocarbons (PAHs), or N-nitroso compounds (NOCs)—all of which may lead to cancer development.

“The findings suggest that dietary modification with more plant food and less animal food may be a potential strategy for primary prevention against the development of bladder cancer,” they said.

The present analysis included 63,275 Chinese Singaporeans between 45 and 74 years of age who completed semi-quantitative food frequency questionnaire at baseline. Bladder cancer occurred in 250 participants over a mean follow-up of 17.6 years. The mean age at cancer diagnosis was 60.8 years.

Compared with those who remained cancer-free, those who had bladder cancer were older, more likely to be male and ever smokers, and less likely to be physically active (p<0.05). Participants with incident bladder cancer also had a lower intake of vitamin A.