A diet high in whole grain, bran and cereal fiber lowers the risk of liver cancer, a new study found.
But an increased intake of fruit or vegetable fiber did not have an effect, US scientists found.
Those who ate the most whole grains in their diet had a 37 percent lower risk than those whose diets were sparse of the healthy grains.
A high bran diet also reduced the risk by 30 percent while germ reduced it by 11 percent.
US researchers tracked 77,241 women and 48,214 men in their 50s and 60s for 24 years. Those with higher intake of whole grains, bran and cereal fiber had a lower risk of liver cancer
Added bran reduced the risk by 31 percent but added germ actually increased the risk by 22 percent.
They added whole grains, bran and cereal fiber reduces insulin resistance, hyperinsulinemia, and inflammation – all known hallmarks of cancer.
Each year over 40,000 Americans and 5,500 Britons are diagnosed with primary liver cancer, or hepatocellular carcinoma – HCC – and it affects more men than women because liver disease in general is more common in men.
It’s more likely to affect people over the age of 65 and is rare below the age of 45.
Dr Xuehong Zhang, Associate Epidemiologist at Brigham & Women’s Hospital and Assistant Professor at Harvard Medical School said: ‘Increased intake of whole grains and possibly cereal fiber and bran could be associated with reduced risk of HCC among adults in the United States.’
He explained: ‘Whole grains are a major source of dietary fiber and consist of bran, germ, and endosperm, compared with refined grains that contain only the endosperm.
‘The whole grains are good sources of dietary fiber, vitamins, minerals, phytonutrients, and other numerous nutrients, which are removed during the refining process.
‘Consumption of whole grains and dietary fiber, especially cereal fiber, has been associated with lower risk of obesity, type 2 diabetes, and nonalcoholic fatty liver disease,which are known predisposing factors for HCC.
‘In addition to improving insulin sensitivity and metabolic regulation and decreasing systemic inflammation, intake of whole grains and dietary fiber may improve gut integrity and alter gut microbiota composition, thereby leading to increased production of microbiota-related metabolites, including short-chain fatty acids, particularly butyrate.
‘Gut integrity, the composition of gut microbiota, and metabolites may play an important role in the development of liver diseases, including HCC.’
So the study followed 77,241 women and 48,214 men with a mean age of 63.4 taking part in the Nurses’ Health Study and the Health Professionals Follow-up Study.
Their intake of whole grains, their subcomponents (bran and germ), and dietary fiber (cereal, fruit, and vegetable) were assessed every four years over an average follow-up of 24.2 years.
Those in the highest tertiles of whole grain and dietary fiber intake were slightly older, had lower BMI, exercised more, drank less, did not smoke, more likely to take aspirin and had higher intake of fruits, vegetables, total folate, multivitamin, and dietary vitamin D, but less fat compared with those in the lowest tertiles.
A total of 141 patients were diagnosed with HCC.
Dr Zhang said: ‘Interestingly, compared with fruit or vegetable fiber, cereal fiber has been shown in our study and other cohort studies to be more consistently associated with lower risk of total mortality, cardiovascular disease, type 2 diabetes, and colorectal cancer.
‘However, our results on the association of cereal fiber with HCC risk could have been due to chance.
‘Alternatively, a potential explanation is that fruits and vegetables, particularly fruit juice, contain sugar or added sugar such as fructose and sucrose, which may lead to hepatic damage and nonalcoholic fatty liver disease, thereby masking the potential benefit of fruit- or vegetable-fiber intake.
‘Overall, the exact reasons for such a difference remain unknown and require further investigation.’
He added while more research was needed he concluded: ‘If our findings are confirmed, increasing whole grain consumption may serve as a possible strategy for prevention of primary HCC.’
The study was published in JAMA Oncology.