DNC News


DNC NEWS: Wrong about Fat

March 4, 2006

Subject: Link between fat consumption and breast cancer melts away

For the last twenty years we preached that switching to a low fat diet was protective against breast cancer.  We were wrong.  A new study published in the February 6 issue of JAMA showed no significant benefit to women who lowered their fat intake.

The logic for promoting a low fat diet to lower risk of breast cancer was simple enough.  High fat diets increase estrogen production. Higher estrogen levels are associated with higher risk of developing breast cancer.  In parts of the world where fat intake is low the risk of breast cancer is also low.  The classic example is Thailand where women have a drastically lower breast cancer risk than in the United States.  Fat intake in Thailand is also a fraction of that here.  High fat diets are associated with earlier menarche and the increased number of menstrual cycles a woman undergoes logically should increase risk. But who says the answers in life have to be simple?  To quote Park Hill's artist and philosopher, Peg Meagher, "Biology is messy."  Just because this explanation sounded reasonable and some early studies lent support, didn't make it true.

The JAMA study reported on an eight year intervention which assigned 19,541 women to a low fat diet and compared the number that developed breast cancer to a group of 29,941 women who continued on a regular diet.  The data showed no significant statistical difference in the number who developed breast cancer. The experimental group developed 655 cases of breast cancer compared to 1,072 in the control group.  That means 3.35% of the women following a low fat diet developed breast cancer compared to 3.66% of the women  who continued to  happily eat the way they wanted.  This small difference was not statistically different and it certainly wasn't the major difference in cancer rates that had been predicted.  Critics will argue that the low fat dieters still ate too much fat; in the end 29% of their daily calories came from fat compared to 37% for the control group. Others will say the study didn't go long enough. Instead of 8 years maybe you need to go 20 years to see anything?  As conducting this study came with a $410 million price tag, it is unlikely anyone will be in a rush to run a longer version .

Most reasonable people will, and should, read this and understand that lowering dietary fat will not prevent breast cancer. (JAMA. 2006;295:629-642. Low-Fat Dietary Pattern and Risk of Invasive Breast Cancer: The Women's Health Initiative Randomized Controlled Dietary Modification Trial)

Not only did the data show no change in breast cancer risk, there was no change in risk for colon cancer, heart disease, stroke, or cardiovascular disease either in the women attempting to eat less fat.

It is interesting how much medical opinion can change over the years.  For many this instability is difficult. For some people it is as if they have switched their faith from church to science for an explanation of their place in the universe.  They seek the same emotional support from science and modern medicine as they once did from religion.  Scientific understanding changes over time and offers little in the way of enduring dogma when it comes to how to live one's life.  But enough philosophizing.



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