DrG's Medisense Feature Article

Breast Cancer Part IV: Fat, Obesity and Exercise
March 2012
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Fat:  Many scientists believed for a long time that dietary fat contributed to breast cancer.  Large studies comparing women in mid-life who ate a lot versus a little of dietary fat have seemingly disproved this dogma.  

I say seemingly because 1) dietary recall in mid-life is notoriously inaccurate, and 2) none of the studies address life-long or childhood fat intake.  Since cancer starts long before you feel a lump, adjusting diet in mid-life may be like trying to board a train that left the station years ago.  

Obesity, not dietary fat, seems to be the true risk factor for post-menopausal breast cancer (and a bunch of other cancers, too), even though high fat diets frequently make people obese.   Pre-menopausal breast cancer is linked to hormones, genetic factors and possibly environmental exposures, not so much to obesity.  

Exercise:  The one preventive behavior that has withstood much scrutiny is exercise.  Lifetime total physical activity reduces the risk of post-menopausal breast cancer.  There is so much data about obesity and a sedentary lifestyle increasing post-menopausal breast cancer risk that I don’t need to argue the case with a lot of data.  

Which is the stronger risk factor?  Probably obesity.  Exercise attenuates the breast cancer risk of obesity, but doesn’t eliminate it.  As weight goes up and exercise goes down, cancer risk increases.  Optimizing one and compensate when the other is suboptimal.  In any given age group, overweight women who exercise more than one hour per week have the same risk of cancer as normal weight women who don’t exercise.  More than an hour per week of exercise by obese women drops cancer risk to that of overweight women who don’t exercise.  

Risk factors are only risk factors and work as predictors for populations, not individuals.  There are women of normal weight who exercise regularly, eat vegetables and don’t drink much alcohol who get breast cancer anyway.  We don’t know why.  If you are worried about risk, you can hedge your bets by exercising, and eating lots of vegetables and modest portions of everything else to maintain an ideal weight.╣