Following a low-fat diet may lengthen survival for post-menopausal women diagnosed with breast cancer, suggests a strong new study that offers important insights into the potential impact of diet on survivorship. The study, partially funded by AICR, was published in the Journal of Clinical Oncology.
Lasting just over 16 years, this study is the largest and longest randomized controlled trial (RCT) to investigate how dietary fat affects survival after breast cancer diagnosis. Previous research in this area was mostly observational and those findings were mixed.
The most recent AICR report on breast cancer survivorship found hints that consuming relatively low amounts of fat – especially saturated fat – before a diagnosis may lengthen survival. But the link was not a strong one and more research was called for.
"This study provides the best evidence so far that patients consuming relatively high amounts of dietary fat could significantly improve their long-term survival after a breast cancer diagnosis by reducing fat intake and increasing fruit and vegetables,” says Nigel Brockton, PhD, AICR Director of Research. "However, limiting fat intake is just one of the many ways in which cancer patients can help improve their outcomes by adopting the AICR/WCRF recommendations, particularly regarding physical activity and achieving and maintaining a healthy body weight."
The study included almost 50,000 women, ages 50-79, with no history of breast cancer. At the start of the study all the participants reported that at least 32 percent of their total calories were from fat.
Women were randomly assigned to either a low-fat diet or a comparison group. Almost 20,000 of the women were asked to follow the low-fat diet, where the goal was to reduce fat intake to 20 percent of daily calories while increasing intake of fruits, vegetables and whole grains. The rest of the women were were asked to follow their usual diet.
The dietary intervention lasted 8.5 years and during that time, women in the low-fat group reported that they consumed less fat. The daily calories from fat went from 38 percent at entry to 24 percent, says lead author Rowan T Chlebowski, MD, PhD., City of Hope National Medical Center. The women also boosted their fruit, vegetable, and grain intake. Even though weight loss was not a goal, these women experienced modest weight loss, about 3 percent loss after 1 year.
Then, after the intervention stopped, the researchers continued to track the women's diet and health. (The women were all part of the Women's Health Initiative, a national health study.) For the next eight years the women filled out questionnaires regularly about what they were eating, how much they were exercising and other lifestyle habits.
According to the self-reports, the women who had been part of the low-fat diet group continued to eat less fat than the comparison group.
After 16.1 years from the start of the study, 3,030 of the women had been diagnosed with breast cancers. Compared to the women who had continued on their usual diet, there were 16 percent fewer deaths among the women in the low-fat diet group.
Breast cancer was the most common cause of death, followed by other cancers and cardiovascular disease. Yet as the authors point out, pinpointing the cause of death after breast cancer can be challenging given that cancer treatments can play a role in cardiac problems and other disease.
Analysis of a select group of the women found that the usual-diet group had a greater percent of women with obesity and with higher waist circumference – 35 inches or more – who died during the course of the study than the low-fat group. Mortality after a diagnosis was seen when women consumed 37 percent or more of daily calories from dietary fat.
The average fat intake for US adult women is almost 34 percent, according to the Centers for Disease Control and Prevention.
"Certainly weight loss could have played a role but the effect was seen even after we adjusted for the weight loss," says Chlebowski. “These results suggest that only a modest reduction in fat intake with minimal weight loss could achieve positive results,” the paper concludes.
The latest government dietary guidelines recommends that individuals limit their saturated fat to less than 10 percent of calories per day. AICR recommends that all survivors limit foods high in both added sugar and fat. Both can lead to weight gain, a factor linked to numerous cancers, including post-menopausal breast.
Along with AICR, the study was supported by the National Heart, Lung, and Blood Institute and the National Cancer Institute.
Sources: Rowan T. Chlebowski et al. Low-Fat Dietary Pattern and Breast Cancer Mortality in the Women’s Health Initiative Randomized Controlled Trial. Journal of Clinical Oncology 2017 35:25, 2919-2926.
CDC/National Center for Health Statistics, Diet/Nutrition. Last updated May 2017. h
Published on October 17, 2017