Questioning Nutritional Studies
Since the 1970s, it has been generally accepted that eating a lot of fiber would protect you from getting colon cancer. Then about 5 years ago, some studies came out showing that eating more fiber had no effect.
Now a new study finds that the association between fiber and colon cancer depends on how you evaluate the diet.
The authors of this study looked at 579 patients who developed colorectal cancer and 1996 matched controls. The patients completed 4- to 7-day food diaries and also filled out food-frequency questionnaires.
The researchers found that when they analyzed the data on the basis of the food-frequency questionnaires, they found no relation between fiber intake and colon cancer. But when they did the same on the basis of the food diaries, they did.
This is an important finding for us, not so much because we're all going to get colon cancer but because food-frequency questionnaires are a standard way of trying to document what people eat. This study says that this method is inaccurate.
That doesn't surprise me. I write down everything I eat, but sometimes I forget to do so until later. And by dinnertime, I often can't remember what I had for breakfast that same day. There's no way I'm going to remember how often I ate chicken or beef or anything else in the past month.
My diet differs depending on the season. And if I roast a chicken or a leg of lamb (I buy a whole grass-fed lamb from neighbors every fall) and don't have guests, I'll have it two or three times a day until it's gone. My diet also differs in other ways. If I find a new food that doesn't make my blood sugar go up a lot, I tend to eat it at meal after meal because it's new. Then I get tired of it and move on to something else.
So saying how often in the past X months I ate a particular food would be pretty meaningless even if I could remember.
Hence (because of this study, not my faulty memory) if some nutritional study purports to show that wowzaberries prevent diabetes or make us smarter, we should take that news with a grain of salt. It could be true. Or not.
A lot of nutritional research is really meaningless. At least we now have a study that shows this is true.