Lifestyle advice is the second most common breast health advice for women after “get a mammogram”. Women are told to limit alcohol, control their weight, not smoke, and nurse any babies they may have. Yet each of these behaviors actually has a very small relationship to breast cancer risk. Everyone knows someone who did all the so-called “right things” and still developed metastatic breast cancer. And nearly everyone who has lived with a breast cancer diagnosis has faced the judgment and unsolicited advice of others on what she did or didn’t do—and what she should do now.
There are far too few studies on the primary prevention of breast cancer—preventing women from getting the disease in the first place. We certainly need non-pharmacologic, non-toxic options for prevention. And whole-body health is important, since it doesn’t do much good to prevent a death from breast cancer only to die of something else. Yet, the net effect of so much diet and exercise advice is that people start blaming women for getting breast cancer. And we know that not everyone has the access and resources they need to follow all this lifestyle advice. So any study about diet and breast cancer risk can understandably bring a strong emotional response for many women, and the promotion of its conclusions runs the risk of reinforcing the “blame women for not doing the right things to avoid getting breast cancer” narrative.
That being said, I do want to report on a study presented at SABCS this year that evaluated overall breast cancer survival in the Women’s Health Initiative dietary modification randomized controlled trial.
This study enrolled nearly 50,000 women between the ages of 50 and 79, with a modest risk of breast cancer according to the GAIL model. Women in the study were randomized to receive a low-fat dietary intervention in an effort to improve survival. The goal was to reduce dietary fat intake—to a very-low, and quite hard to achieve, target of just 20% calories from fat—as well as to increase fruit, vegetable and grain consumption. Weight loss itself was not a goal of the study.
During the period of intervention, which lasted more than eight years, 1,767 women were diagnosed with breast cancer. Initial analysis found there were fewer breast cancers diagnosed in the low fat dietary group, although the finding was not statistically significant. Women in the low-fat diet group who were diagnosed with breast cancer were somewhat less likely to die from the disease.
This presentation at SABCS reported secondary analysis of mortality by subgroups, based on tumor characteristics. This analysis included data from over eight years of post-intervention follow-up and an average of 16 median years of follow up. They evaluated deaths from breast cancer and deaths from other causes (what the presenter called “deaths after breast cancer”).
Women on the low-fat diet were less likely to die in the study’s time period, but equally likely to die from breast cancer as those in the placebo group. The presenter said that two groups appeared to have the greatest benefit from limiting dietary fat: women with larger waist circumference as well as those with a higher fat diet when entering the study (at baseline). The presenter also noted that there was no benefit to the low-fat diet for women over age 70.
Because it is quite difficult to reduce fat consumption to just 20% of total calories—let alone maintain that for eight years—there is some skepticism about the real-world implications of the study. The presenter speculated that perhaps the threshold is not low fat, but rather high fat intake. Thus the threshold to see benefit might be higher than 20% and more achievable than previously thought.
There is a long list of questions which the study cannot answer. The study didn’t look at types of fat, for example—animal or vegetable. It didn’t look at timing of intervention and if there are specific ages that have greatest impact. Nor did the study look at artificial chemicals in food and food packaging.
Each person must balance their quality of life on a particular diet with possible health benefits. Many people consider changes to their diet after being diagnosed with breast cancer. It can often feel like one thing within a person’s control, and a way to try to reduce the risk of recurrence or prolong stability with metastatic disease. But many so-called healthful directly contradict each other. For example, Paleo diets include high meat and fat consumption while vegan diets are plant-based. Similarly, many low-fat foods are often laden with sugar. And adherents to each often view the other as foolhardy.
There’s no saying what the optimal diet is, but this study suggests that low to modest fat intake seems like a good idea for overall health.