Diet Does Not Affect Breast Cancer?


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The objective of The Women’s Healthy Eating and Living (WHEL) Randomized Trial 1 was to:

Assess whether a major increase in vegetable, fruit, and fiber intake and a decrease in dietary fat intake reduces the risk of recurrent and new primary breast cancer and all-cause mortality among women with previously treated early stage breast cancer.

The conclusion of this “controlled trial of dietary change in 3088 women previously treated for early stage breast cancer” was:

Among survivors of early stage breast cancer, adoption of a diet that was very high in vegetables, fruit, and fiber and low in fat did not reduce additional breast cancer events or mortality during a 7.3-year follow-up period.
The study was a randomized controlled trial of dietary change in 3088 women previously treated for early stage breast cancer who were 18 to 70 years old at diagnosis.

The intervention group consisted of 1,537 women randomly assigned to receive a telephone counselling program supplemented with cooking classes and newsletters that promoted daily targets of 5 vegetable servings plus 16 oz (470 ml) of vegetable juice; 3 fruit servings; 30 g of fiber; and 15% to 20% of energy intake from fat.

The comparison group consisted of 1,551 women who were provided with print materials describing the “5-A-Day” dietary guidelines.

This made headlines all over the world. This is the proof people were waiting for – that changes to your diet has no impact on breast cancer. Medical practitioners, dieticians and the public now have the evidence that changing your diet is not helpful in recovery from breast cancer.
The authors claim that the diet is “very high in vegetables, fruit, and fiber and low in fat”. The assessment criteria is to determine the effects of “a major increase in vegetable, fruit, and fiber intake and a decrease in dietary fat intake”.

Let’s look at the figures from the paper.

 GroupBaseline48 mon72 monChange
Total vegetables servings/dIntervention3.
Total fruit servings/dIntervention3.53.63.4-0.1
Vegetables and fruit servings/dIntervention7.410.09.21.8
Fiber g/dIntervention21.
Energy from fat %Intervention28.527.128.90.4
Energy intake kcal/dIntervention171915521538-181
Body weightIntervention73.574.274.10.6

It appears that the authors are deliberately being deceptive. The study states that:

At 4 years, relative differences in mean intake between study groups were 65% for vegetable servings, 25% for fruit servings, 30% for fiber, and −13% for energy intake from fat.
  • The study was over a period of 7 years. Why are the authors quoting 4-year figures and not the 7-year figures?
  • The authors are comparing the relative changes of the intervention group with the control group. The control group ate less fruit and vegetables and consumed more fat than they did at the beginning of the study.
  • If you compare the changes that the intervention group made then the results are not nearly as convincing. Over the 7 year period, the intervention group consumed an additional 1.8 servings of fruit and vegetables per day and consumed an additional 3.1 g of fiber per day. This is not a great increase.  The study’s claims that that the intervention “diet was very high in vegetables, fruit, and fiber” is simply not true.
  • The recommended total dietary fiber intake for women is 25 to 30 grams a day from food. The average of 24.2 g/d does not represent a very high fiber intake.
  • The study was based on a self-reporting questionnaire which tend to be unreliable.
  • The intervention slightly increased the % energy from fat (28.5% to 28.9% fat). This is not a low-fat diet.
  • The intervention group were overweight at the beginning of the study and are slightly heavier at the end of the 7 years.
  • If the intervention group really decreased the energy intake by 11% they would have decreased their weight.

It is important to note that the reported values are averages. If the goal is to reach a particular outcome, such as a recommended fiber intake, then all participants should be meeting the target.

The conclusions this long and expensive study is not supported by the evidence presented. The reason that the study did not show any significant findings is because there were no significant changes to the women’s diet.

 Harvard Nurses’ Health Study

The Harvard Nurses’ Health Study is another famous study that showed diet did not have an effect on breast cancer. Nearly 90,000 nurses were studied for 20 years. They were divided into 10 groups based on the fat intake as a % of energy. The group with the lowest fat consumption ate less than 20% fat with the highest group consuming more than 49%. However, the risk of breast cancer remained the similar in the 10 groups.

The study did show that:

  • as the amount of fat decreased, the amount of protein and animal protein increased
  • the amount of fruit and vegetables remained low for all groups

Replacing whole milk (50% energy from fat) with low-fat milk (33% energy from fat), replacing red meat with fish and poultry and consuming low-fat deserts is does not constitute a low-fat diet.

Once again the study is comparing different versions of an unhealthy, high-fat, high-protein, high animal-based diet and finding out that that there is no real difference in the outcomes.

Fat and Cancer

Below is a graph from the paper  Fat and Cancer 2 by Kenneth Carroll. Carroll - Fat and Cancer

It shows a strong correlation with saturated fat intake and death rate from breast cancer.  However, the emphasis that fat and fat alone is implicated in breast cancers is a mistake.  It is important to note that there is:

  • a strong correlation with saturated fat intake and animal protein intake
  • a strong correlation with saturated fat intake and fat intake
  • no relationship with plant-based fat intake and  breast cancer rates


  1. J. P. Pierce, L. Natarajan, B. J. Caan et al “Influence of a diet very high in vegetables, fruit, and fiber and low in fat on prognosis following treatment for breast cancer,” Journal of the American Medical Association, vol. 298, no. 3, pp. 289–298, 2007.
  2. K. Carroll, L. Braden, J. Bell, and R. Kalamegham, “Fat and Cancer,” Cancer, vol. 58, pp. 1818–1825, 1986.

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