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Evid Based Nurs 9:112-113 doi:10.1136/ebn.9.4.112
  • Treatment

A low fat dietary pattern intervention did not reduce breast cancer, colorectal cancer, or CVD in postmenopausal women


 
 Q Does a dietary modification intervention promoting a low fat dietary pattern reduce risk of breast cancer, colorectal cancer, or cardiovascular disease (CVD) in postmenopausal women?

METHODS

GraphicDesign:

3 reports of different outcome measures of a randomised controlled trial (Women’s Health Initiative [WHI]).

GraphicAllocation:

{concealed}.*

GraphicBlinding:

blinded (physician adjudicators verifying outcomes, {data collectors, data analysts, and monitoring committee}*).

GraphicFollow up period:

mean 8.1 years.

GraphicSetting:

40 clinical centres in the US.

GraphicParticipants:

48 835 postmenopausal women 50–79 years of age (mean age 62 y) with baseline fat intake ⩾32% of total calories. Exclusion criteria were previous cancer (except for non-melanoma skin cancer) in the past 10 years, medical conditions with predicted survival <3 years, type 1 diabetes, adherence concerns such as alcoholism or dementia, or frequent consumption of meals prepared away from home.

GraphicIntervention:

low fat dietary pattern intervention (n = 19 541) or no dietary intervention (n = 29 294). The dietary modification intervention promoted dietary change with the goals of reducing total fat to 20% of energy intake and increasing fruits and vegetables to ⩾5 servings per day and grains to ⩾6 servings per day. A specially trained nutritionist led 18 group sessions in the first year and quarterly sessions thereafter. Each participant received her own fat gram goal according to her height. Participants self monitored their fat, fruit, and vegetable intake and also engaged in individual interview sessions that used reflective listening techniques, targeted message campaigns, and personalised feedback on fat intake. Control group participants received Dietary Guidelines for Americans and other health related materials but were not asked to make dietary changes.

GraphicOutcomes:

invasive breast cancer; invasive colorectal cancer; coronary heart disease (CHD) (myocardial infarction [MI] or CHD death); a composite of CHD and revascularisation; stroke; total CVD (MI, CHD death, revascularisation, and stroke); and a global index (first occurrence of invasive breast cancer, invasive colorectal cancer, CHD, or death from other causes).

GraphicPatient follow up:

44 351 women (91%) were alive with outcome data submitted at study end; all women were included in the intention to treat analysis. {As implemented, the study had 60% power to detect a 14% reduction in breast cancer, 40% power to detect a 14% reduction in colorectal cancer, and 40% power to detect a 14% reduction in CHD with dietary modification intervention compared with control}.*

MAIN RESULTS

The dietary modification and control groups did not differ for invasive breast cancer, invasive colorectal cancer, or any CVD outcomes (table). Secondary analyses showed that the intervention led to a greater reduction in breast cancer among women with higher baseline percentage of energy from fat (hazard ratio [HR] 0.78, 95% CI 0.64 to 0.95) and a greater reduction in CHD risk among women who achieved the lowest intake of saturated fat (HR 0.81, CI 0.69 to 0.96). The intervention had no adverse effects on concentrations of triglycerides, high density lipoprotein cholesterol, or insulin. Mean reductions in percentage of energy from fat were lower in the intervention group than the control group (mean difference between groups at 6 y –8.2, CI –8.3 to –8.0), but only 14% of women met the dietary target of 20% energy from fat.

CONCLUSION

A dietary modification intervention promoting a low fat dietary pattern did not reduce risk of breast cancer, colorectal cancer, or cardiovascular disease in postmenopausal women.

A modified version of this abstract appears in ACP Journal Club.

Commentary

  1. Catherine Goetz-Perry, RN, MN
  1. Victorian Order of Nurses, Grey-Bruce
 Owen Sound, Ontario, Canada

      The WHI Dietary Modification Trial evaluated the effects of a low fat dietary pattern intervention with increased fibre intake on primary outcomes of colorectal cancer and invasive breast cancer and secondary outcome of CVD in postmenopausal women. Previous studies linking risk of breast and colorectal cancer to dietary fat intake had observational, cohort, and case-control study designs. A recent review found a small but significant reduction in CV risk in trials of reduced or modified fat intake lasting 2 years, but the analysis did not target postmenopausal women.1

      Strengths of the WHI study include a randomised controlled design, long term follow up, a large number and diversity of participants, and high retention rates. Limitations include heterogeneity among effects, which may have been caused by differences in settings or population characteristics; overestimation of reductions in dietary intake because of self report; underestimation of first occurrence of outcomes because of self report or lack of specific diagnostic tests; low power; and underestimation of treatment effects because few participants achieved or sustained intervention goals for reduced fat and increased fibre, fruit, and vegetable intake. Furthermore, differences between the intervention and control groups may have been minimised by changes in US national dietary guidelines for type and reduction of fat intake to total energy intake and recommendations for increased fibre and fruit and vegetable intake during the study. Generalisability is limited to populations with dietary patterns similar to those in the US.

      The study findings are relevant to nurses involved in population health strategies in public health and primary healthcare settings and to advanced practitioners and nurses working with youth and women in health promotion / disease prevention in primary health care, acute care, and community care settings.

      Results suggest that a single dietary pattern approach (eg, lower fat intake as percentage of total energy intake) may not lend itself to specific risk reduction for cancers and CVD in postmenopausal women. A need exists to target dietary fat intake counselling and intervention based on risk or presence of specific disease. Subgroup analyses showed a possible trend to lower low density lipoprotein concentrations and CHD rates through very low levels of saturated and trans fat or very high levels of fruit and vegetable intake. To reduce individual CVD disease risk, aggressive and targeted dietary fat reduction would be required, including replacement of saturated and trans fat with monounsaturated and polyunsaturated fat, consumption of fish for θ fatty acids, and adoption of a Mediterranean style diet combined with regular exercise.2 There was also evidence for breast cancer reduction in women who had a high percentage of energy from fat at baseline. Therefore, women with diets routinely high in fat should be targeted to adopt a low fat dietary pattern combined with high fibre intake to reduce breast cancer risk.3,4

      If reductions in fat intake and increases in fruit, vegetable, and fibre intake are expected to reduce risk of cancers and CVD in women, dietary changes must begin well before mid-life and be sustained over the long term. It is likely that adherence to and maintenance of dietary changes benefit from an aggressively introduced high intensity, long term intervention. Further research is required to identify the duration of dietary change required.

      References

      Low fat dietary pattern intervention v no diet intervention in postmenopausal women at mean 8.1 years*

      
 
 Q Does a dietary modification intervention promoting a low fat dietary pattern reduce risk of breast cancer, colorectal cancer, or cardiovascular disease (CVD) in postmenopausal women?

      Footnotes

      • * Information provided by authors.

      • For correspondence: Dr R L Prentice, Fred Hutchinson Cancer Research Center, Seattle, WA, USA. rprentice{at}whi.org Dr S A Beresford, University of Washington, Seattle, WA, USA. beresfrd{at}u.washington.edu Dr B V Howard, MedStar Research Institute, Hyattsville, MD, USA. Barbara.v.howard{at}medstar.net

      • Source of funding: National Heart, Lung, and Blood Institute.

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