We previously discussed the wide discrepancy in cancer rates between the U.S. and Japan, and considered that the differences in dietary fat intake might be responsible in part for it.

If we go back to the 1970s when these hypotheses were being formulated and discussed, the average U.S. intake of fat was 40% of calories. In Japan, the average intake of fat was close to 20%, a huge difference. Indeed, it is likely that this low fat intake was responsible in part for the reduced height of the Japanese relative to their Western counterparts—when Japanese migrated to the West, not only did they acquire the cancer rates of the West, they also increased in height.

So does having a really low-fat diet prevent breast cancer? In 1993, a study known as the Women’s Health Initiative (WHI) randomized 48,835 postmenopausal women to one of two groups—either a 20% fat diet or their normal diets. Great efforts were made to ensure that the experimental group achieved their dietary goal and, in fact, they did achieve an average 24% fat diet, a remarkable achievement in my view, given how unpalatable a 20% fat diet is to a Westerner.

This intervention was maintained for eight full years. Nonetheless, at 8.1 years of follow up, there was no statistically significant difference in the breast cancer incidence rate between the two groups. Interestingly, there was no effect on colorectal cancer incidence either. (The study was designed to look at the impact of a low-fat diet on both cancers.)

At about the same time (in 2005), a truly remarkable study was presented at the annual meeting of the American Society of Clinical Oncology and subsequently published. This study was led by investigators of the American Health Foundation, a small center specialized in studies of cancer prevention, located on the campus of New York Medical College in Westchester County, now a part of Touro.

This study, the Women’s Intervention Nutrition Study (WINS), recruited 2,437 postmenopausal women with non-metastatic breast cancer, mostly Stage I and II, who had undergone surgery for their tumors and who had then received the standard treatment for their breast cancers with chemotherapy and hormonal therapy. They were then randomized to receive either a 20% fat diet or to continue their usual diet.

Again, the investigators made heroic efforts to keep the women adherent to the low-fat diets, with frequent group meetings, special low-fat recipes, frequent phone calls for encouragement and monitoring, regular meetings with dietitians, etc. Adherence to the 20% fat diet was thus extremely high.

At a follow-up of 60 months, the breast cancer relapse rate in the intervention group was 9.8% versus 12.4% in the control group, representing a 24% reduction in relapses for the dietary intervention (p=0.034). To put this in context, the impact of a low-fat diet, albeit an extremely low-fat diet, on breast cancer relapse was as profound or more profound than the impact of chemotherapy or hormonal therapy. Actually, this effect was superimposed on top of those treatments.

Just recently, a follow-up of the WHI study we described above was published. It addressed this same question, i.e., the effect of the low-fat diet on the death rate of breast cancer after being on the low-fat diet for eight years. At almost 20 years of follow-up of this large trial, the low-fat diet continued to have no effect on the incidence of breast cancer. However, the study did find a 21% statistically significant reduction in mortality among the breast cancer cases that occurred in the low-fat experimental group as compared to the control group, confirming the results of the WINS study.

Just to give some context, the FDA generally requires two randomized trials demonstrating the efficacy of a new drug in order to approve the marketing of the drug, although these requirements have been somewhat relaxed for newer chemotherapy agents. If a new chemotherapy drug had two randomized trials that showed the efficacy that a low-fat diet demonstrated in these two trials, and in the absence of any toxicity, we would at least be considering its use. But I should also note two caveats: both of these studies only included postmenopausal women with breast cancer, not premenopausal; and while the WINS study had improved recurrence-free survival, it did not show improved overall survival, which is considered a stronger result.

I would offer one other comment on this topic, which is that, in parallel to the WINS study at the American Health Foundation, there was also a PINS study—Prostate Intervention Nutrition Study. Its goal was to investigate whether the same 20% fat diet could reduce the recurrence/mortality rate of prostate cancer. Unfortunately, the study had to be terminated early because the men in the study were totally unable to adhere to the dietary requirements necessary for the study. Thus, this question remains unanswered. I will refrain from making comments on gender differences.

Alfred I. Neugut, MD, PhD, is a medical oncologist and cancer epidemiologist at Columbia University Irving Medical Center/New York Presbyterian and Mailman School of Public Health in New York.

This article is for educational purposes only and is not intended to be a substitute for professional medical advice, diagnosis, or treatment, and does not constitute medical or other professional advice. Always seek the advice of your qualified health provider with any questions you may have regarding a medical condition or treatment.