Debating low-fat diets and cancer risk

Does what you eat really matter? Conflicting reports make it difficult to determine what we should and should not eat. The media report on nutrition studies regularly, with results that often are contradictory and complicated.

In 2006 the results of the Women’s Health Initiative (WHI) were released in the Journal of the American Medical Association. The study -- the largest of its kind -- was conducted by the National Institutes of Health.

One of the trials tested the diet of 48,000 post-menopausal women. The women were randomly assigned to an intervention or control group.

The intervention group received instructions and behavior modification education to help them limit their fat intake to 20 percent of their total calories. The control group was told not to reduce their fat intake.

Scientists followed the women for an average of eight years. When the results were released earlier this year, the media reported that the study showed eating a low-fat diet did not lower the risk of breast cancer, colon cancer, or heart disease.

Look More Closely

A closer examination of the results of the study indicate that the findings were not that definite.

“The findings are hard to interpret and hard to tease out,” says Denise Snyder, MS, RD, CSO, LDN, an advanced practice oncology nutritionist at the Duke University School of Nursing. She points out several confounding factors related to the study:

• Many of the women in the intervention group did not lower their fat intake to the desired level, at least not over the course of the entire study. In addition, women in the control group lowered their fat intake even though they were told to keep it constant. What if the women in each group actually adhered to the fat intake levels requested?

• The study lasted eight years. The amount of fat we consume may matter, but so might the amount of time we actually follow a low-fat diet. What if the women would have stayed on the low-fat diet for a longer period of time?

• The study looked at total fat, and researchers did not specify “good” fats versus “bad” fats.

• Researchers only looked at older women.

Some Groups May Benefit

In fact, the results did show that for certain subgroups of women, a low-fat diet did reduce the risk of breast cancer.

A 15 to 20 percent overall reduction in breast cancer incidence occurred among women in the low-fat diet group who began the study with the highest baseline fat consumption, and among women who most strictly adhered to the study’s dietary-fat goals.

Other subsets also showed results that were promising, but since they appeared in the margin of error researchers cannot be fully confident that the cancer rates were reduced due to diet.

“Results of the study can be confusing, and that’s unfortunate,” says Snyder. “While researchers try to draw conclusions from a large pool of women, each individual is different.”

Even Lower than Low Fat

In May 2005 results from the Women’s Intervention Nutrition Study, funded by the National Cancer Institute and the Breast Cancer Research Foundation, were released.

These researchers tested whether a low-fat diet was helpful in preventing a recurrence of breast cancer among older women with early-stage disease.

In this study, fat intake was limited to less than 15 percent of total calories -- a much more stringent diet than prescribed in the WHI study. Roughly 50 women at Duke participated in the trial, which suggested that low-fat diets could protect against recurrence.

Prevention Versus Control

Snyder believes that in the future there will be genetic testing to see how susceptible one is to getting a particular cancer and based on this, doctors will prescribe a specific diet or treatment to that person to lessen the risk.

“Right now, what we do know is that people tend to think of cancer in general terms, yet not all cancers behave alike,” she explains.

“We also have to remember that cancer is a progressive disease. What initiates cancer is not necessarily what makes it continue to grow. There’s a difference in prevention versus control.”

Stick with Common Sense

Researchers acknowledge that more research with longer follow-up time is needed to continue to explore the link between what we put in our mouths and the risk of cancer.

In the meantime, the seemingly mixed messages can be overwhelming and frustrating.

Snyder -- along with other researchers -- cautions that although the link between a low-fat diet and cancer has not been confirmed, this doesn’t give us license to splurge on cakes and doughnuts.

"Related to that, these high-fat foods are going to have more calories," Snyder says. "What do excess calories lead us to? More pounds. What we do know in terms of cancer is that weight gain is a big risk factor."

Reducing fat and increasing fruits and vegetables and whole grains in our diets will ensure that our bodies are getting enough nutrients and may contribute to our overall health.