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


METHODS
A randomized, controlled, primary prevention trial conducted at 40 US clinical centers from 1993 to 2005.


METHODS
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.


METHODS
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.


METHODS
Invasive breast cancer incidence.


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.


BACKGROUND
ClinicalTrials.gov Identifier: NCT00000611.
Prentice
Ross L
RL
Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, Wash 98109, USA. rprentice@whi.org
Caan
Bette
B
Chlebowski
Rowan T
RT
Patterson
Ruth
R
Kuller
Lewis H
LH
Ockene
Judith K
JK
Margolis
Karen L
KL
Limacher
Marian C
MC
Manson
JoAnn E
JE
Parker
Linda M
LM
Paskett
Electra
E
Phillips
Lawrence
L
Robbins
John
J
Rossouw
Jacques E
JE
Sarto
Gloria E
GE
Shikany
James M
JM
Stefanick
Marcia L
ML
Thomson
Cynthia A
CA
Van Horn
Linda
L
Vitolins
Mara Z
MZ
Wactawski-Wende
Jean
J
Wallace
Robert B
RB
Wassertheil-Smoller
Sylvia
S
Whitlock
Evelyn
E
Yano
Katsuhiko
K
Adams-Campbell
Lucile
L
Anderson
Garnet L
GL
Assaf
Annlouise R
AR
Beresford
Shirley A A
SA
Black
Henry R
HR
Brunner
Robert L
RL
Brzyski
Robert G
RG
Ford
Leslie
L
Gass
Margery
M
Hays
Jennifer
J
Heber
David
D
Heiss
Gerardo
G
Hendrix
Susan L
SL
Hsia
Judith
J
Hubbell
F Allan
FA
Jackson
Rebecca D
RD
Johnson
Karen C
KC
Kotchen
Jane Morley
JM
LaCroix
Andrea Z
AZ
Lane
Dorothy S
DS
Langer
Robert D
RD
Lasser
Norman L
NL
Henderson
Maureen M
MM
D000368:Aged; D015415:Biomarkers / Q000097:blood; D001835:Body Weight; D001943:Breast Neoplasms / Q000453:epidemiology / Q000517:prevention & control*; D008078:Cholesterol, LDL / Q000097:blood; D015930:Diet Records; D018752:Diet, Fat-Restricted; D005260:Female; D005500:Follow-Up Studies; D012739:Gonadal Steroid Hormones / Q000097:blood; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D017698:Postmenopause; D011322:Primary Prevention; D016016:Proportional Hazards Models; D012306:Risk; D012738:Sex Hormone-Binding Globulin / Q000032:analysis
D015415:Biomarkers; D008078:Cholesterol, LDL; D012739:Gonadal Steroid Hormones; D012738:Sex Hormone-Binding Globulin