Nonstarch polysaccharides may be chemopreventive against colorectal cancer

Dietary intake of nonstarch polysaccharides (NSPs) appears to be beneficial in reducing the risk of colorectal cancer (CRC) in Chinese Singaporeans, as reported in a study.

There was an inverse, dose-dependent relationship between dietary NSP and the risk of CRC, such that higher intakes were associated with a greater risk reduction relative to the lowest intake (Q2: hazard ratio [HR], 0.99, 95 percent confidence interval [CI], 0.88–1.11; Q3: HR, 0.98, 95 percent CI, 0.87–1.11; Q4: HR, 0.84, 95 percent CI, 0.73–0.95; p_trend=0.006). [Cancer Res Commun 2022;2:1304-1311]

Notably, the chemopreventive effect of dietary NSP was more pronounced for colon cancer (Q4 vs Q1: HR, 0.79, 95 percent CI, 0.67–0.93; p_trend=0.003) than rectal cancer (Q4 vs Q1: HR, 0.92, 95 percent CI, 0.74–1.13; p_trend=0.53).

Meanwhile, dietary fibre intake had no significant effect on the risk of CRC overall or histologic subtypes.

“To our knowledge, this is the first prospective cohort study that evaluated the association of both dietary fibre and NSP with colorectal cancer risk in Chinese adults. Previous studies focus on dietary fibre in Western populations,” according to the investigators, adding that the lack of studies evaluating the effect of dietary NSP on CRC risk might be due to the difficulties of differentiating between fibre and NSP.

NSPs are complex carbohydrates that are naturally present in many foods. They make up most of the diet’s fibre and contain cellulose, chitin glucans, gums, inulin, mucilages, and pectins. The insoluble NSP (cellulose and hemicellulose) in wheat, maize, and rice has laxative properties; on the other hand, the soluble NSP (mixed-link β-glucans) in oats, barley, rye, and beans helps lower cholesterol levels and maintain healthy glucose and insulin levels. [Crit Rev Food Sci Nutr 2012;52:899-935; Front Pediatr 2021;8:620189; Br J Cancer 1994;69:937-942]

“We found the inverse association for NSP intake was primarily for colon cancer, but not for rectal cancer. The biology behind the protective effect of NSP is not fully understood, but undigested NSP, when partially fermented by colon bacteria, produces short-chain fatty acids (propionate, acetate, and butyrate) and increases the stool weight and decreases the transit time of faeces in the colon, all thought to be protective against CRC,” the investigators explained.

“[Conversely,] dietary fibre was not protective against the development of CRC, which is consistent with the null results by the clinical trial studies,” they added. [N Engl J Med 2000;342:1156-1162; N Engl J Med 2000;342:1149-1155; J Natl Cancer Inst 1995;87:1760-1766]

The current analysis used data from the Singapore Chinese Health Study and included 61,321 cancer-free middle-aged or older Chinese Singaporeans. All participants completed a validated semi-quantitative food frequency questionnaire coupled with the Singapore Food Composition Database to provide information regarding fibre and NSP intakes at baseline.

A total of 2,140 participants developed CRC (1,355 colon cancer and 785 rectal cancer) over an average follow-up of 17.5 years. The mean baseline age was 59.5 years for colorectal cancer cases and 56.3 years for those free of colorectal cancer. Participants who developed colorectal cancer tended to be older, male, ever smokers, heavy drinkers, or to have a family history of CRC (p<0.05 for all).

In addition, participants who developed colorectal cancer, on average, had a lower intake of dietary fibre and NSP compared with those who remained free of colorectal cancer (p≤0.01 for all).

The findings, according to the investigators, suggest that NSP may play an important role in primary prevention of CRC. “The potential protective effect of NSP, independent of dietary fibre, on CRC development warrants further study.”