Pierce JP et al. (2007) Influence of a diet very high in vegetables, fruit, and fiber and low in fat on prognosis following treatment for breast cancer: the Women's Healthy Eating and Living (WHEL) randomized trial. JAMA 298: 289–298

Although the role of a healthy diet in the prevention of cancer has been much discussed, clinical trial data do not support an association between a diet high in fruit and vegetables and a reduced risk of cancer. Supporting previous findings, in a multi-institutional randomized controlled trial Pierce at al. have demonstrated that a major increase in the consumption of fruit, vegetables and fiber and a decrease in dietary fat intake does not reduce the risk of recurrent or new primary breast cancer in women previously treated for this disease.

In total, 3,088 women (mean age 53 years) were randomized to either a dietary-intervention group (n = 1,537) or a control group (n = 1,551). The major intervention was intensive telephone counseling, which was supplemented by cooking classes and by newsletters promoting high daily targets for the intake of fruit and vegetables. Patients in the control group received information on the '5-a-day' dietary guidelines. The intervention group achieved—and maintained over a 4-year period—markedly increased intakes of vegetables (+65%), fruit (+25%), and fiber (+30%), and decreased intakes of energy from fat (–13%). Over a mean follow-up of 7.3 years, the incidences of invasive breast cancer in the two groups were comparable (adjusted hazard ratio 0.96, 95% CI 0.80–1.14; P = 0.63). Furthermore, no significant difference in overall mortality was noted between the groups (adjusted hazard ratio 0.91, 95% CI 0.72–1.15; P = 0.43).