Low-fat dietary pattern and risk of colorectal cancer: the Women's Health Initiative Randomized Controlled Dietary Modification Trial.
BACKGROUND
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.


METHODS
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.


METHODS
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.


METHODS
Invasive colorectal cancer incidence.


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.


CONCLUSIONS
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.


BACKGROUND
ClinicalTrials.gov Identifier: NCT00000611.
Beresford
Shirley A A
SA
Department of Epidemiology, University of Washington, Seattle, WA 98195-7236, USA. beresfrd@u.washington.edu
Johnson
Karen C
KC
Ritenbaugh
Cheryl
C
Lasser
Norman L
NL
Snetselaar
Linda G
LG
Black
Henry R
HR
Anderson
Garnet L
GL
Assaf
Annlouise R
AR
Bassford
Tamsen
T
Bowen
Deborah
D
Brunner
Robert L
RL
Brzyski
Robert G
RG
Caan
Bette
B
Chlebowski
Rowan T
RT
Gass
Margery
M
Harrigan
Rosanne C
RC
Hays
Jennifer
J
Heber
David
D
Heiss
Gerardo
G
Hendrix
Susan L
SL
Howard
Barbara V
BV
Hsia
Judith
J
Hubbell
F Allan
FA
Jackson
Rebecca D
RD
Kotchen
Jane Morley
JM
Kuller
Lewis H
LH
LaCroix
Andrea Z
AZ
Lane
Dorothy S
DS
Langer
Robert D
RD
Lewis
Cora E
CE
Manson
JoAnn E
JE
Margolis
Karen L
KL
Mossavar-Rahmani
Yasmin
Y
Ockene
Judith K
JK
Parker
Linda M
LM
Perri
Michael G
MG
Phillips
Lawrence
L
Prentice
Ross L
RL
Robbins
John
J
Rossouw
Jacques E
JE
Sarto
Gloria E
GE
Stefanick
Marcia L
ML
Van Horn
Linda
L
Vitolins
Mara Z
MZ
Wactawski-Wende
Jean
J
Wallace
Robert B
RB
Whitlock
Evelyn
E
D000236:Adenoma / Q000453:epidemiology / Q000517:prevention & control; D000368:Aged; D001241:Aspirin / Q000627:therapeutic use; D003111:Colonic Polyps / Q000453:epidemiology / Q000517:prevention & control; D015179:Colorectal Neoplasms / Q000453:epidemiology / Q000517:prevention & control*; D018752:Diet, Fat-Restricted; D015914:Estrogen Replacement Therapy; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D016013:Likelihood Functions; D008875:Middle Aged; D017698:Postmenopause; D011322:Primary Prevention; D016016:Proportional Hazards Models; D012306:Risk; D012307:Risk Factors
D001241:Aspirin