**2.1 Dietary fiber**

Dietary fiber refers to carbohydrate polymers of plant origin that may or may not be associated to plant lignin [7]. There is convincing evidence that consuming wholegrains and foods containing dietary fiber decrease the risk of developing CRC [8]. A meta-analysis of prospective studies noted a 10% reduction in CRC risk for every 10 g of total dietary fiber consumed on a daily basis [9]. An analysis of specific sources of dietary fiber found that cereal fiber was associated with a dosedependent reduction in risk of 10% for every 10 g consumed; however, fruit fibers, vegetable fibers, and legume fibers were not associated with a significant reduction in risk. A meta-analysis of case-control studies and cohort studies on dietary fiber intake and the incidence of CRC adenoma reported similar findings [10].

The European Prospective Investigation into Cancer and Nutrition (EPIC) supports the protective effect of dietary fiber, as the consumption of cereal fiber was significantly and inversely associated with colorectal cancer, colon cancer, and rectal cancer [11]. A significant inverse association was also noted between colon cancer and combined fruit and vegetable fiber intake, although the study was limited by dietary intake assessment conducted at baseline [12].

The HELGA prospective study agrees with previous studies, as a 26% reduction in colon cancer risk in men was reported for every 10 g of dietary fiber consumed on a daily basis. However, the association was not significant in women, thereby suggesting that dietary fiber may be protective against CRC, but other factors such as phytochemicals, energy intake, body weight, and genetics may be equally influential, as is general dietary pattern [13]. This finding serves to demonstrate that consuming dietary fiber from a variety of sources (cereals, fruits, and vegetables)

**11**

*Effectivity and Modulating Pathways for the Prevention of Colorectal Cancer: Diet, Body Fatness…*

protects against the development of CRC in a dose-dependent manner. Based on the convincing evidence available, it would be reasonable to recommend an increased

Dietary fiber found in wholegrains may protect against the development of CRC by increasing fecal bulk through binding water and decreasing colonic transit time, thereby reducing the potential for fecal mutagens to interact with the colon mucosa, lowering the concentration of potential carcinogens, and exposing the colon mucosa to potential carcinogens for shorter period of time [4, 12, 14–17]. In addition, dietary fiber is fermented by intestinal microbiota into short-chain fatty acids (SCFAs) such as butyrate, which in experimental studies was shown to have antiproliferative and pro-apoptosis properties [4, 14–18]. SCFAs also lower fecal pH in the colon, thus providing a healthy intestinal environment [18], as well as inhibit chronic inflammation and cancer cell migration/invasion in the colon. However, these activities are only effective within certain physiological concentration ranges of SCFAs [18]. Other mechanisms include a reduction in secondary bile acid production [14], as well as enhancing the health of colonocytes [12] by modifying the composition of gut microbiota that can enhance immunity [18]. High-fiber diets may also reduce insulin resistance, a risk factor for CRC [7, 8, 14–16], by decreasing insulin growth factor (IGF)-1 activity, decreasing systemic inflammation via the production of SCFAs, and enhancing levels of colonic microbiota, thereby strengthening the intestinal barrier [4, 15, 16]. The anticarcinogenic properties of wholegrains also include being a source of antioxidants such as vitamin E, selenium, copper, zinc, and phytochemicals, as well as decreasing body adiposity [4, 14]. Wholegrains are also sources of lignans, phytoestrogens, and phenolic compounds [14], with many of these bioactive compounds being largely found in the bran and germ of the grain. To illustrate the plausible anticarcinogenic properties of several phenolic acids, experimental studies have showcased their ability to stimulate anti-oxidative activity [19].

Dairy products include milk (whole or skim milk), cheese (fresh, cottage, and hard cheese), and yogurt [17]. There is strong probable evidence that consuming dairy products, i.e., total dairy, milk, cheese, and dietary calcium, decreases the risk of CRC [8]. Dose-response meta-analyses of dairy products, milk, and dietary calcium were statistically significant with little or no heterogeneity. However, the evidence for cheese was not as strong as for other dairy products, with prospective studies finding no association between cheese intake and CRC risk, thus qualifying the level of evidence as not conclusive [7]. A pooled analysis reported significant inverse associations when comparing the highest with the lowest levels of milk intake and dietary calcium. Hence, there is evidence of plausible mechanisms in humans [8]. As there is probable evidence that milk consumption protects against CRC, it may be reasonable to encourage the consumption of milk for the prevention of CRC [4].

Dairy products contain a variety of bioactive compounds that could be related to simultaneous positive or negative effects on carcinogenesis. The overriding theory underpinning the possible protective effect of dairy products against cancer risk is related to their calcium and to a lesser extent, their vitamin D, lactoferrin, and fermentation products [4, 20, 21]. In addition, dairy products have the ability to

*DOI: http://dx.doi.org/10.5772/intechopen.84764*

*2.1.1 Mechanism*

**2.2 Dairy products**

*2.2.1 Mechanism*

intake of wholegrains to help reduce the risk of CRC [4].

protects against the development of CRC in a dose-dependent manner. Based on the convincing evidence available, it would be reasonable to recommend an increased intake of wholegrains to help reduce the risk of CRC [4].
