Abstract IA12: Food and nutrition and colorectal cancer: Patterns for prevention
Authors: Lampe Johanna W. 
Published: March 2017

Abstract
Diet is a complex environmental exposure. Evidence from epidemiologic studies and experimental studies in animal models has indicated that diet and components of diet have an important role in modulating risk of colorectal cancer (CRC). The WCRF/AICR Continuous Update Project Report routinely evaluates epidemiologic studies of diet and cancer risk. In the 2011 report on diet and CRC, the reviewers determined that the evidence was convincing that consumption of foods containing dietary fiber protect against CRC and intake of red meat, processed meat, ethanol from alcoholic beverages are causes of CRC. The evidence that physical activity protects against colon cancer and that body fatness and abdominal fatness (consequences of diet and inactivity) contribute to CRC was also labeled as convincing. Consumption of garlic, milk, and calcium was reported as probably protective, while the evidence was limited that non-starchy vegetables, fruits and foods containing vitamin D protect against CRC, or that foods containing iron, and also cheese, foods containing animal fats, and foods containing sugars are causes of CRC. Experimental studies in animals and randomized controlled trials in humans have helped to expand our understanding of the wide array of mechanisms by which dietary constituents may cause or prevent CRC, including through modulation of inflammation and immune function, carcinogen metabolism, hormone and growth-factor regulation, DNA repair capacity, cell-cycle control, and proliferation and apoptosis. Increasingly, the importance of diet-gut microbe interactions are being recognized; diet can influence the amount and types of microbes present in the gut, and gut microbial metabolism of dietary constituents produces compounds that may have positive or adverse effects on CRC risk.
In the past decade, there has been a growing emphasis on identifying dietary patterns associated with lower cancer risk, with the recognition that, although many dietary constituents have been suggested to have preventive effects, they are not consumed in isolation and the role of diet in cancer prevention might be maximized when dietary patterns are considered versus any one single component. Diet quality has been studied using statistical clustering or factor analysis within a data set, an agnostic approach that can potentially identify new patterns important to CRC risk. Another approach is to use diet quality scoring systems defined a priori. These are derived based on emerging evidence of diet and disease risk, have algorithms that can be applied across multiple data sets, and provide the potential for more direct translation to public health messages. A variety of diet quality indices have been developed, including Healthy Eating Index (HEI-2005; HEI-2010), Alternative Healthy Eating Index 2010 (AHEI), the Dietary Approaches to Stop Hypertension (DASH) index, and indices based on the Mediterranean diet. A role for diet quality in CRC risk has been reported in the context of several prospective cohort studies. Reedy et al. (Am. J. Epidemiol., 2008), testing associations between scores on 4 diet quality indices and CRC risk in the National Institutes of Health-AARP (NIH-AARP) Diet and Health Study, reported that higher scores on all 4 indices were associated with a lower risk of CRC in men, but that, in women, only the HEI-2005 score showed an association. In the same NIH-AARP population, 4 different methods of indexing adherence to the DASH diet were associated with lower risk of CRC in men, but only 2 of the DASH indexing methods were associated with a significantly lower CRC risk in women (Miller et al, Am. J. Clin Nutr., 2013). Recently, in the Women's Health Initiative Observational Study, a cohort of postmenopausal US women, higher HEI-2010 diet quality index scores were associated with lower risk of CRC and, similarly, higher DASH diet quality index scores were associated with a 22%–28% lower risk of CRC (Vargas et al, Am. J. Epidemiol., 2016). In these studies, indices of Mediterranean-diet adherence have been less consistently associated with CRC risk. Future use of experimental diets in animal studies that capture the complexity of the human diets may help to further characterize the effectiveness of these diet patterns and the components of them. Understanding the impact of the totality of complex diet patterns is needed further inform approaches for CRC prevention.
Citation Format: Johanna W. Lampe. Food and nutrition and colorectal cancer: Patterns for prevention. [abstract]. In: Proceedings of the AACR Special Conference on Colorectal Cancer: From Initiation to Outcomes; 2016 Sep 17-20; Tampa, FL. Philadelphia (PA): AACR; Cancer Res 2017;77(3 Suppl):Abstract nr IA12.