So, maybe all that dietary fiber isn’t as healthy as you thought

Fiber-enriched foods have gotten popular to encourage weight loss and protect against chronic diseases. But a recent study suggests that a diet high in processed fiber could increase some people’s risk of developing liver cancer.

The risk of liver cancer may be highest with people who have a silent vascular deformity called a portosystemic shunt, which allows bile acid to leak into the bloodstream.

The findings, reported in the journal “Gastroenterology,” add to the growing body of evidence that gut health plays an important role in disease.

Liver core biopsy showing liver disease with Steatosis on the left and Mallory hyaline on the right. These are major risk factors for the most common form of liver cancer - hepatocellular carcinoma.

Researchers found that about one in 10 otherwise healthy lab mice got liver cancer after consuming a diet high in inulin, a refined, plant-based fermentable fiber that is sold in supermarkets as a health-promoting prebiotic and is often found in processed foods. The finding was surprising since liver cancer is rare in mice, according to a report in SciTech Daily.

“Dietary inulin is good in subduing inflammation, but it can be subverted into causing immunosuppression, which is not good for the liver,” said Beng San Yeoh, a postdoctoral fellow and a study author, in an interview with the University of Toledo.

The study found that mice with excess bile acid in their blood were predisposed to liver injury, but only those fed inulin developed hepatocellular carcinoma, a deadly primary liver cancer. In fact, 100% of the mice with high bile acids in their blood developed cancer when fed inulin. None of the mice with low bile acids developed cancer when fed the same diet.

The link between bile acid in the bloodstream and liver cancer appears to apply to humans.

The test team checked bile acid levels in serum samples collected between 1985 and 1988 as part of a large cancer prevention study. They found that, in the 224 men who developed liver cancer, baseline blood bile acid levels were twice the level of those of men who did not develop liver cancer.

Beyond the laboratory, this research might help clinicians identify people who are at higher risk of liver cancer years in advance of any tumors forming. It would require adding blood serum screens to standard blood panels conducted routinely.

Such screenings could identify people who are at higher risk of liver cancer – which could be prevented by a more cautious consumption of fiber, according to the study’s report.

Researchers found high total fiber intake reduced the risk of liver cancer by 29% in men whose serum bile acid levels were in the lowest quartile of their sample. But, in men whose blood bile acid levels were in the top quarter, high fiber intake translated into a 40% increased risk of liver cancer.

It suggests that fiber – though generally thought to be healthy – could pose its own risks in some people.