Diet is thought to be partly responsible for about 30% to 40% of all cancers. But diet alone is unlikely to be the “cause” or the “cure” of cancer. In the 1970s, the theory that a high-fat diet increased breast cancer risk became popular, and some people still believe that theory. Still, studies done since that time have offered mixed results.
The very large WHEL (Women’s Healthy Eating and Living) study was designed to see if a very stringent diet that was low in fat and high in vegetables, fruit, and fiber made a difference in survival or breast cancer recurrence (the breast cancer coming back) in women who had been diagnosed. The results were published in 2007 and showed that the diet had no effect on survival or recurrence, which surprised many people.
In 2017, results from the Women’s Health Initiative Trial suggested that postmenopausal women who ate a low-fat diet after a breast cancer diagnosis were less likely to die from any cause compared to women who ate a diet that was higher in fat. Still, researchers wanted to know how much the low-fat diet affected survival.
A secondary analysis of the Women’s Health Initiative data suggests that postmenopausal women who eat a low-fat diet after being diagnosed with breast cancer are more likely to be alive 10 years after diagnosis compared to women who ate a diet that was higher in fat after being diagnosed.
The research was published online on May 24, 2018 by JAMA Oncology. Read the abstract of “Association of Low-Fat Dietary Pattern With Breast Cancer Overall Survival: A Secondary Analysis of the Women’s Health Initiative Randomized Clinical Trial.”
This research is part of the very large Women’s Health Initiative Clinical Trial and the Women’s Health Initiative Observational Study. Both studies are commonly called the WHI. Together, the two studies include information from more than 161,608 postmenopausal women who were ages 50 to 79 when they joined between 1993 to 1998. The WHI wants to find any links between health, diet, and lifestyle factors and health problems such as cancer.
The researchers started with information from 48,835 postmenopausal women who enrolled in the WHI between 1993 and 1998. When they enrolled in the study, none of the women had been diagnosed with breast cancer and all reported eating a diet that was more than 32% fat. The women were randomly assigned to one of two diet plans:
- 19,541 women (40%) were told to eat a low-fat diet (fat intake was supposed to be only 20% of the diet); these women also participated in group sessions led by a nutritionist to teach the women how to reduce their fat intake
- 29,294 women (60%) were told to eat their usual diet and received educational materials on healthy eating
The women followed the diet plans for about 8.5 years. The women in both groups did about the same amount of exercise.
While the women were following the diet plans, 1,764 women were diagnosed with breast cancer:
- 671 women eating a low-fat diet were diagnosed
- 1,093 women eating their usual diet were diagnosed
To do this analysis, the researchers looked at survival information for the 1,764 diagnosed women.
The women were followed for 11.5 years after being diagnosed. During the follow-up period, 516 women died. Fewer women eating a low-fat diet died compared to women eating their usual diet.
- 68 women eating a low-fat diet died from breast cancer
- 27 women eating a low-fat diet died from heart disease
- 36 women eating a low-fat diet died from other cancers
- 120 women eating their usual diet died from breast cancer
- 64 women eating their usual diet died from heart disease
- 65 women eating their usual diet died from other cancers
Breast cancer survival and overall survival for women who ate the low-fat diet was higher compared to women who ate their usual diet.
Ten years after diagnosis:
- 82% of women eating a low-fat diet were alive
- 78% of the women eating their standard diet were alive
"Our study demonstrates that postmenopausal women on a low-fat diet who were diagnosed with breast cancer lived longer," said Rowan Chlebowski, M.D., Ph.D., research professor in the Department of Medical Oncology and Therapeutics Research at City of Hope. Dr. Chlebowski is the WHI’s principal investigator. "Following a low-fat diet -- at any point in your life -- can have tremendous health benefits."
While these results are encouraging, it’s important to keep several things in mind:
- The study relied on the women accurately reporting what they ate and then estimating the fat content in the food. Sometimes people don’t remember everything they eat or how much of something they eat, which would affect the results of the study.
- The study didn’t look to see if the women stuck to their breast cancer treatment plans completely. Stopping a treatment, such as hormonal therapy, early would affect the study results.
- The study only looked at postmenopausal women diagnosed with breast cancer. The results can’t be applied to premenopausal women with breast cancer.
- While the women in the study had no history of breast cancer, it’s not clear if any of the women had a family history of breast cancer. This could possibly affect the results of the study.
If you’re a postmenopausal woman who’s been diagnosed with breast cancer, it makes sense to make healthy diet and lifestyle choices to keep your risk of recurrence as low as it can be and your overall health the best it can be, including:
- eating a diet low in added sugar and processed foods
- eating a diet rich in unprocessed, nutrient-dense foods (foods that have the most vitamins, minerals, and healthy compounds)
- exercising regularly at the highest intensity level you’re comfortable with
- avoiding alcohol
- not smoking
It also makes sense to stick to your treatment plan. Treatments such as chemotherapy and radiation therapy can require trips to the hospital or doctor’s office for several months. You also may need to take hormonal therapy medicines for 5 or 10 years after surgery. You get the best results when you follow your plan completely and on schedule.
For tips on how to overcome common problems with following a treatment plan, visit the Breastcancer.org Staying on Track With Treatment pages.