Vitality

Low-Fat Diet May Help Postmenopausal Women With Breast Cancer Reduce Risk Of Death

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A new study finds that a sustained low-fat diet may offer a boost in survival rates following breast cancer, but how seriously should we take its findings? Pixabay, Public Domain

Postmenopausal women who stick to a low-fat diet for at least ten years may have a slight buffer against breast cancer’s long term effects, suggests new research presented this week at the American Association for Cancer Research (AACR) annual meeting.

The researchers analyzed data from an earlier study of 48,835 healthy postmenopausal women ages 50 to 79 years, called The Women’s Health Initiative Dietary Modification trial. From 1993 to 1998, the study’s authors randomly enrolled 19,541 in an intervention group that sought to reduce their daily fat intake to 20 percent of the day’s calories, complete with regular group counseling sessions led by a nutritionist. And the remaining 29,294 women were given standard care and diet-related educational material. During the dietary intervention period, which lasted an average of 8.3 years, 1,767 women were diagnosed with breast cancer.

For the current study, the authors checked in on how these women were faring healthwise as of August 2014. They found that there was a minor improvement in survival rates afterwards for the low-fat group, with 487 deaths in total over the years. Eighty-two percent of the low-fat group survived for at least 10 years following their diagnosis compared to 78 percent of the control group.

"This was the first time we had examined the deaths after breast cancer among this group, and we found that a sustained low fat diet increased the survival rates among postmenopausal women after a breast cancer diagnosis," said lead author Dr. Chlebowski in a statement. "The study also suggests that women would need to remain on the low fat diets to maintain the benefits of the dietary intervention."

Heartening as these findings might appear at first glance, though, we should be careful not to oversell them, nor the overall usefulness of a low-fat diet. For one, previous research examining this same data has come to much more disappointing conclusions. A 2014 study concluded that the long-term rates of breast and other cancers weren’t noticeably different between the two groups and other studies have found the same miniscule difference for cardiovascular disease and weight loss respectively.

A possible explanation for these lackluster findings is that the women in the low-fat group increased their fat intake once the dietary intervention ended, thus negating any protective effect, but the health differences during the trial itself weren’t particularly dramatic either. For example, the women in the low-fat group did see an average weight loss of 5 pounds during the first year of the trial, 4 pounds better than their control counterparts. By the middle of the 8th year, though, that difference was less than a pound. This same sort of conclusion has been found elsewhere as well.

Similarly, while the original study showed that the low-fat group had a slightly lower risk of developing more dangerous breast cancers, such as estrogen receptor positive/progesterone receptor–negative tumors, it wasn’t statistically significant. That means the finding wasn’t clear enough to strongly exclude the possibility of having simply arisen by chance. It's a weakness that applies to many of the current study’s results as well. 

Although there were 20 percent fewer deaths from breast cancer directly in the low-fat group, Chlebowski admitted in an interview with HealthDay that this difference wasn’t significant. The only truly noteworthy contrast came when examining non-cancer related deaths following diagnosis — the low fat group saw 40 deaths versus 94 in the control group. The majority of this particular protective effect possibly came from a reduced risk of cardiovascular disease.

With these looming caveats, it’s difficult to strongly conclude, as Chlebowski and his colleagues have, that a low-fat diet in of itself offers any noticeable impact on the health outcomes following breast cancer — especially given that the impact, if there, fades away the moment the diet stops. 

None of this is to say that eating healthier isn’t worthwhile or beneficial for your long-term health, mind you, it just means the focus on low fat as a primary dietary goal may be misguided. Other research has begun to show the type of fat consumed regularly matters much more than the amount of fat in a diet, with trans fat in particular being singled out as conclusively harmful.

Source: Chlebowski R, Aragaki A, Anderson G, et al. Low-fat dietary pattern and breast cancer mortality in the Women's Health Initiative (WHI) randomized trial. AACR 2016. 2016.

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