Starch and breast cancer link?

cause of breast cancer? nah.

A study presented at the Breast Cancer Symposium of the American Association for Cancer Research claims there’s a link between starch and breast cancer recurrence.  My verdict: a very lame conclusion, and no clear link.

Here’s the study: almost 3000 breast cancer survivors were surveyed by phone once/year, for 7 years, about what they ate the previous day.  The diet data (for just one day) was compared to recurrence of breast cancer.  Result: women who had a recurrence had, on average, increased carb intake by 2.3 grams/day while women who did not have a recurrence decreased carbs by about 2.7 grams/day.  Conclusion: carbs caused recurrence.

Wrong.

There are so many problems with this study and this conclusion.  Where to begin?

  • 2.3 more or 2.7 less grams/day – both are extremely trivial amounts, just 9 calories more than average or 11 calories less per day in carbs, equivalent to a range of about 1 potato chip.  How did researchers come up with such a tiny specific number based on vague phone surveys.  Respondents are notoriously prone to mis-reporting food intake.  Phone interviewers won’t have any way to validate the amounts they’re being told.  The only way to accurately measure food intake is to lock someone in a ward for years and weigh and measure everything they eat.  Relying on phone interviews is a terrible way to gather data on food intake.
  • The phone survey only assessed food eaten on the previous day.  What about the other 364 days in the year?  To conclude that one day is an accurate representation is impossible.
  • Maybe the women who ate a teensy bit less carbs made some other dietary change that was helpful.  It’s highly likely that some breast cancer patients decided that they were going to change their diets as a result of the cancer, adding more vegetables or fruit perhaps.  If they’re eating more of one thing, they end up eating less of something else, possibly bread or noodles or doughnuts or cookies.
  • Eating slightly fewer carbs could have been a reflection of women eating less overall food.  Weight loss for overweight or obese breast cancer patients can help with survival.  Perhaps the effect had nothing to do with carbs, and more to do with lower calories and attempted weight loss.  However, the trivial calorie difference from carbs alone (11/day) isn’t enough to cause meaningful weight loss.
  • Maybe the carbs were eaten with something else that was the real issue: additives, artificial sweeteners, unhealthy fats?
  • Maybe there was something else about women who were prone to recurrence anyway: they had a craving for carbs, they had an aversion to other types of foods (meats, vegetables, etc) due to taste changes from medications.  If so, the carbs didn’t cause the recurrence; they were a symptom of a process related to recurrence.

Simplistic conclusions linking one nutrient to some occurrence or disease marker are basically useless, although researchers do these studies all the time.  The mainstream media doesn’t employ nutrition experts to drill through these studies.  They just want a catchy headline to grab attention. If you don’t read beyond the headlines, you end up believing that starch or carbs are linked to breast cancer.  Now you know that was the wrong conclusion.

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