A balanced, lower-fat diet significantly lowers the risk of dying from breast cancer in postmenopausal women, according to new long-term data from the Women’s Health Initiative (WHI) Dietary Modification trial.
“Ours is the first randomized, controlled trial to prove that a healthy diet can reduce the risk of death from breast cancer. The balanced diet we designed is one of moderation, and after nearly 20 years of follow-up, the health benefits are still accruing,” said lead investigator Dr. Rowan Chlebowski from Harbor-UCLA Medical Center in Torrance, California.
About the trial
The trial enrolled 48,835 postmenopausal women with no previous breast cancer and who ate diets that contained at least 32 percent of total daily calories from fat. From 1993 to 1998, the women were randomly assigned to a usual-diet comparison group or a dietary intervention group that aimed to reduce fat intake to 20 percent of daily calories and increase consumption of vegetables, fruit and grains.
The intervention study ended in 2005. Women in the balanced, low-fat diet group has stuck to the diet for roughly 8.5 years. Most of them increased their intake of fruits, vegetables and grains and cut their daily fat intake to 25 percent or less, although most did not reach the 20 percent goal.
The research team was then able to track half of the women for the next 20 years.
A total of 3,374 women developed breast cancer between 1993 and 2013. The low-fat diet did not significantly reduce women’s risk of developing breast cancer. However, women assigned to the low fat dietary pattern during the intervention period had a 21 percent lower risk of death from breast cancer and a 15 percent lower risk of death from any cause during the follow up period.
Postmenopausal women with metabolic syndrome (increased blood pressure, high blood sugar, large waist circumference and elevated cholesterol or triglyceride levels) were especially likely to benefit from the dietary intervention.
These are noteworthy findings. They come from a randomized controlled trial – the strongest evidence for cause and effect – that involved nearly 49,000 women and included two decades of follow up.
But they are not without caveats. The researchers don’t know to what degree these women maintained the low-fat dietary pattern during the follow up.
Yet, the diet modifications the women achieved during the intervention period weren’t drastic; it’s quite possible that the participants were able to maintain such moderate diet changes. But we don’t know.
Even so, this study further emphasizes the importance and possible protective factors of a diet high in plant foods, such as fruits, vegetables and whole grains, in women with breast cancer.
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