Dietary fiber and whole-grain consumption in relation to colorectal cancer in the NIH-AARP Diet and Health Study.
ABSTRACT Whether the intake of dietary fiber can protect against colorectal cancer is a long-standing question of considerable public health import, but the epidemiologic evidence has been inconsistent.
The objective was to investigate the relation between dietary fiber and whole-grain food intakes and invasive colorectal cancer in the prospective National Institutes of Health-AARP Diet and Health Study.
The analytic cohort consisted of 291 988 men and 197 623 women aged 50-71 y. Diet was assessed with a self-administered food-frequency questionnaire at baseline in 1995-1996; 2974 incident colorectal cancer cases were identified during 5 y of follow-up. The Cox proportional hazards model was used to estimate the relative risks (RRs) and 95% CIs.
Total dietary fiber intake was not associated with colorectal cancer. The multivariate RR for the highest compared with the lowest intake quintile (RR(Q5-Q1)) was 0.99 (95% CI: 0.85, 1.15; P for trend = 0.96). In analyses of fiber from different food sources, only fiber from grains was associated with a lower risk of colorectal cancer (multivariate RR(Q5-Q1): 0.86; 95% CI: 0.76, 0.98; P for trend = 0.01). Whole-grain intake was inversely associated with colorectal cancer risk: the multivariate RR(Q5-Q1) was 0.79 (95% CI: 0.70, 0.89) for the whole cohort (P for trend < 0.001). The association with whole grain was stronger for rectal than for colon cancer.
In this large prospective cohort study, total dietary fiber intake was not associated with colorectal cancer risk, whereas whole-grain consumption was associated with a modest reduced risk.
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ABSTRACT: Intake of wholegrain foods has been associated in large prospective cohort studies with decreased rates of diseases such as type 2 diabetes, ischaemic heart disease and hypertension. Multiple mechanisms for the protectiveness of wholegrain foods have been reported. Health authorities in western countries recommend wholegrains as one of the major food sources in a healthy diet, otherwise rich in vegetables, legumes and low-fat dairy. However, the existing evidence for the intake of wholegrains is highly subject to confounding. Many of the results seen in the prospective cohort studies have not been borne out in randomised controlled trials or good-quality meta-analyses. The recommended intake of wholegrains suggested in some countries is well above what there is evidence for. Products labelled wholegrain have variable quantities of the intact grain and differ widely in their effect on blood glucose. Excessive quantities may add to glycaemic load, and anti-nutrients in wholegrains may have adverse health consequences. With the rate of diabetes and obesity increasing, some researchers have questioned the role of grains as part of a healthy diet. Palaeolithic diets, those that are more in keeping with our evolutionary legacy, contain no grains or dairy, but are rich in vegetables, meat, fish and eggs, with the inclusion of some tubers. Smaller trials in animals and humans comparing a palaeolithic diet to a grain-based diet show improved metabolic profiles in the former.Food and Nutrition Sciences 01/2012; 03(08). DOI:10.4236/fns.2012.38152
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ABSTRACT: Previous epidemiological studies on the relation between dietary legume consumption and risk of colorectal cancer (CRC) remain controversial. We conducted a meta-analysis based on prospective cohort studies to investigate the association between dietary legume consumption and risk of CRC. Fourteen cohort studies were finally included, containing a total of 1903459 participants and 12261 cases who contributed 11628960 person-years. We found that higher legume consumption was associated with a decreased risk of CRC (RR, relative risk = 0.91; 95% CI, confidence interval = 0.84-0.98). Subgroup analyses suggested that higher legume consumption was inversely associated with CRC risk in Asian (RR = 0.82; 95% CI = 0.74-0.91) and soybean intake was associated with a decreased risk of CRC (RR = 0.85; 95% CI = 0.73-0.99). Findings from our meta-analysis supported an association between higher intake of legume and a reduced risk of CRC. Further studies controlled for appropriate confounders are warranted to validate the associations.