Dietary fiber and the risk of colorectal cancer and adenoma in women.

Fuchs CS, Giovannucci EL, Colditz GA, et al.: N Engl J Med 340 (3): 169-76, 1999. 
Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA.

BACKGROUND: A high intake of dietary fiber has been thought to reduce the risk of colorectal cancer and adenoma. METHODS: We conducted a prospective study of 88,757 women, who were 34 to 59 years old and had no history of cancer, inflammatory bowel disease, or familial polyposis, who completed a dietary questionnaire in 1980. During a 16-year follow-up period, 787 cases of colorectal cancer were documented. In addition, 1012 patients with adenomas of the distal colon and rectum were found among 27,530 participants who underwent endoscopy during the follow-up period. RESULTS: After adjustment for age, established risk factors, and total energy intake, we found no association between the intake of dietary fiber and the risk of colorectal cancer; the relative risk for the highest as compared with the lowest quintile group with respect to fiber intake was 0.95 (95 percent confidence interval, 0.73 to 1.25). No protective effect of dietary fiber was observed when we omitted, adjustment for total energy intake, when events during the first six years of follow-up were excluded, or when we excluded women who altered their fiber intake during the follow-up period. No significant association between fiber intake and the risk of colorectal adenoma was found. CONCLUSIONS: Our data do not support the existence of an important protective effect of dietary fiber against colorectal cancer or adenoma.

Lack of effect of a low-fat, high-fiber diet on the recurrence of colorectal adenomas. Polyp Prevention Trial Study Group.

Schatzkin A, Lanza E, Corle D, et al. N Engl J Med 342 (16): 1149-55, 2000.  National Cancer Institute, Bethesda, MD, USA.

BACKGROUND: We tested the hypothesis that dietary intervention can inhibit the development of recurrent colorectal adenomas, which are precursors of most large-bowel cancers. METHODS: We randomly assigned 2079 men and women who were 35 years of age or older and who had had one or more histologically confirmed colorectal adenomas removed within six months before randomization to one of two groups: an intervention group given intensive counseling and assigned to follow a diet that was low in fat (20 percent of total calories) and high in fiber (18 g of dietary fiber per 1000 kcal) and fruits and vegetables (3.5 servings per 1000 kcal), and a control group given a standard brochure on healthy eating and assigned to follow their usual diet. Subjects entered the study after undergoing complete colonoscopy and removal of adenomatous polyps; they remained in the study for approximately four years, undergoing colonoscopy one and four years after randomization. RESULTS: A total of 1905 of the randomized subjects (91.6 percent) completed the study. Of the 958 subjects in the intervention group and the 947 in the control group who completed the study, 39.7 percent and 39.5 percent, respectively, had at least one recurrent adenoma; the unadjusted risk ratio was 1.00 (95 percent confidence interval, 0.90 to 1.12). Among subjects with recurrent adenomas, the mean (+/-SE) number of such lesions was 1.85+/-0.08 in the intervention group and 1.84+/-0.07 in the control group. The rate of recurrence of large adenomas (with a maximal diameter of at least 1 cm) and advanced adenomas (defined as lesions that had a maximal diameter of at least 1 cm or at least 25 percent villous elements or evidence of high-grade dysplasia, including carcinoma) did not differ significantly between the two groups. CONCLUSIONS: Adopting a diet that is low in fat and high in fiber, fruits, and vegetables does not influence the risk of recurrence of colorectal adenomas.

Low-Fat Dietary Pattern and Risk of Invasive Breast Cancer  The Women's Health Initiative Randomized Controlled Dietary Modification Trial

Ross L. Prentice, PhD; et al JAMA. 2006;295:629-642.

Context  The hypothesis that a low-fat dietary pattern can reduce breast cancer risk has existed for decades but has never been tested in a controlled intervention trial. Objective  To assess the effects of undertaking a low-fat dietary pattern on breast cancer incidence.  Design and Setting  A randomized, controlled, primary prevention trial conducted at 40 US clinical centers from 1993 to 2005.  Participants  A total of 48 835 postmenopausal women, aged 50 to 79 years, without prior breast cancer, including 18.6% of minority race/ethnicity, were enrolled.  Interventions  Women were randomly assigned to the dietary modification intervention group (40% [n = 19 541]) or the comparison group (60% [n = 29 294]). The intervention was designed to promote dietary change with the goals of reducing intake of total fat to 20% of energy and increasing consumption of vegetables and fruit to at least 5 servings daily and grains to at least 6 servings daily. Comparison group participants were not asked to make dietary changes.

Results  Dietary fat intake was significantly lower in the dietary modification intervention group compared with the comparison group. The difference between groups in change from baseline for percentage of energy from fat varied from 10.7% at year 1 to 8.1% at year 6. Vegetable and fruit consumption was higher in the intervention group by at least 1 serving per day and a smaller, more transient difference was found for grain consumption. The number of women who developed invasive breast cancer (annualized incidence rate) over the 8.1-year average follow-up period was 655 (0.42%) in the intervention group and 1072 (0.45%) in the comparison group (hazard ratio, 0.91; 95% confidence interval, 0.83-1.01 for the comparison between the 2 groups). Secondary analyses suggest a lower hazard ratio among adherent women, provide greater evidence of risk reduction among women having a high-fat diet at baseline, and suggest a dietary effect that varies by hormone receptor characteristics of the tumor.

Conclusions  Among postmenopausal women, a low-fat dietary pattern did not result in a statistically significant reduction in invasive breast cancer risk over an 8.1-year average follow-up period. However, the nonsignificant trends observed suggesting reduced risk associated with a low-fat dietary pattern indicate that longer, planned, nonintervention follow-up may yield a more definitive comparison.

Low-Fat Dietary Pattern and Risk of Colorectal Cancer  The Women's Health Initiative Randomized Controlled Dietary Modification Trial

Shirley A. A. et al JAMA. 2006;295:643-654.

Context  Observational studies and polyp recurrence trials are not conclusive regarding the effects of a low-fat dietary pattern on risk of colorectal cancer, necessitating a primary prevention trial. Objective  To evaluate the effects of a low-fat eating pattern on risk of colorectal cancer in postmenopausal women. Design, Setting, and Participants  The Women’s Health Initiative Dietary Modification Trial, a randomized controlled trial conducted in 48 835 postmenopausal women aged 50 to 79 years recruited between 1993 and 1998 from 40 clinical centers throughout the United States. Interventions  Participants were randomly assigned to the dietary modification intervention (n = 19 541; 40%) or the comparison group (n = 29 294; 60%).The intensive behavioral modification program aimed to motivate and support reductions in dietary fat, to increase consumption of vegetables and fruits, and to increase grain servings by using group sessions, self-monitoring techniques, and other tailored and targeted strategies. Women in the comparison group continued their usual eating pattern.

Results  A total of 480 incident cases of invasive colorectal cancer occurred during a mean follow-up of 8.1 (SD, 1.7) years. Intervention group participants significantly reduced their percentage of energy from fat by 10.7% more than did the comparison group at 1 year, and this difference between groups was mostly maintained (8.1% at year 6). Statistically significant increases in vegetable, fruit, and grain servings were also made. Despite these dietary changes, there was no evidence that the intervention reduced the risk of invasive colorectal cancer during the follow-up period. There were 201 women with invasive colorectal cancer (0.13% per year) in the intervention group and 279 (0.12% per year) in the comparison group (hazard ratio, 1.08; 95% confidence interval, 0.90-1.29). Secondary analyses suggested potential interactions with baseline aspirin use and combined estrogen-progestin use status (P = .01 for each). Colorectal examination rates, although not protocol defined, were comparable between the intervention and comparison groups. Similar results were seen in analyses adjusting for adherence to the intervention.

Conclusion  In this study, a low-fat dietary pattern intervention did not reduce the risk of colorectal cancer in postmenopausal women during 8.1 years of follow-up.