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. 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 stringent low fat, high fruit, high vegetable, high fiber diet made a difference in survival or breast cancer recurrence in women who’d been diagnosed. The results published in 2007 showed that the diet had no effect on survival or the cancer coming back, which surprised many people.
A new European study suggests that a diet high in fat, particularly saturated fat, is linked to a greater risk of hormone-receptor-positive breast cancer, as well as breast cancer that is HER2-negative.
The research was published online on April 9, 2014 by the Journal of the National Cancer Institute. Read the abstract of “Dietary Fat Intake and Development of Specific Breast Cancer Subtypes."
The study involved more than 300,000 women from across Europe who were part of the EPIC (European Prospective Investigation into Cancer and Nutrition) study. The EPIC study was designed to look at the relationships between diet, nutrition, lifestyle and environmental factors, and cancer and other diseases.
The researchers figured out how much fat the women were eating by using the answers from food questionnaires the women filled out as part of the EPIC study.
There are three types of fat in food:
- saturated fats are found primarily in foods that come from animals, such as meat and whole-milk products, and in some plant oils, such as coconut and palm oils
- monounsaturated fats are found in many nuts, nut oils, and olive oil
- polyunsaturated fats are found in seafood, fish and fish oil, and corn oil
The researchers also looked at questionnaire results that asked about other breast cancer risk factors, such as drinking alcohol, smoking, pregnancy history, hormone replacement therapy use, weight, and menopausal status.
After 11.5 years of follow-up, 10,062 breast cancer cases were diagnosed. The researchers had information on:
- estrogen-receptor status for 70.6% of the cancers
- progesterone-receptor status for 59% of the cancers
- HER2 status for 22.9% of the cancers
Compared to women who ate the least total fat, women who ate the most total fat had a higher risk of estrogen-receptor-positive, progesterone-receptor-positive breast cancer.
Women who ate the most saturated fat also had a higher risk of estrogen-receptor-positive, progesterone-receptor-positive breast cancer compared to women who ate the least saturated fat. Eating a lot of saturated fat also was linked to a higher risk of HER2-negative breast cancer.
Women who ate the most fat ate about 47.5 grams of fat per day and women who ate the least fat ate about 15.4 grams per day. (For reference, two tablespoons of regular cream cheese has 10 grams of fat. Six pieces of McDonald’s Chicken McNuggets has 18 grams of fat. One medium hardboiled egg has 5 grams of fat. One tablespoon of any type of oil has 14 grams of fat.)
While the results of this study are troubling, it’s important to keep several things in mind.
First, the women in the study had to remember exactly how much and what they ate for the previous year. Unless you keep a detailed food diary every day, this is extremely difficult to do. The women in this study did keep a 7-day food diary, but they had to remember what they ate for the other 51 weeks of the year. So it’s likely that the amount and type of food eaten was misreported.
Second, while the researchers did consider some other risk factors, such as drinking alcohol and smoking, it’s not clear if they asked about the women’s exercise habits. A lack of exercise can lead to worse breast cancer outcomes.
Third, hormone-receptor and HER2-receptor status were determined using immunohistochemistry (IHC) tests, which use a special staining process on fresh or frozen breast cancer tissue removed during biopsy. But different labs used different standards to classify a cancer as either receptor positive or negative, so some cancers were misclassified. Also, hormone-receptor and HER2-receptor status wasn’t available for all the cancers. So there may have been differences between cancers for which the information was available and cancers for which it wasn’t.
So while this study shows an association between eating a high fat diet and a higher risk of hormone-receptor-positive, HER2-receptor-negative breast cancer, it doesn’t prove that the first causes the second. Much more research is needed on the possible link between dietary fat and breast cancer.
Every woman wants to know what she can do to lower her risk of breast cancer. Some of the factors associated with breast cancer -- being a woman, your age, and your genetics, for example -- can't be changed. Other factors can be changed by making healthy lifestyle choices, including:
- eating a healthy diet that’s low in processed foods and sugar
- avoiding alcohol
- maintaining a healthy weight
- exercising daily
- not smoking
By choosing the healthiest lifestyle options possible, you can empower yourself and make sure your breast cancer risk is as low as possible.
To learn more about breast cancer risk factors, visit the Breastcancer.org Lower Your Risk section.