October 2, 2011

Flawed Logic: Eating "Eggs" or "Meat" is Associated with but Does Not CAUSE Cancer

Today the morning news carried this headline: Eggs may Increase Risk Of Lethal Prostate Cancer In Healthy Men. The article starts out by saying that "we already know red and processed meat may increase risk of advanced prostate cancer" and then claims that eggs are just as dangerous.

The actual study is found here:

Egg, red meat, and poultry intake and risk of lethal prostate cancer in the prostate specific antigen-era: incidence and survival. Erin Richman et al., Cancer Prev Res. 2011 Sep 19. [Epub ahead of print]doi: 10.1158/1940-6207.CAPR-11-0354

The study draws its conclusions by looking at 27,607 men followed between 1994-2008. Of these 199 died of prostate cancer. So the researchers analyzed their food consumption and concluded that "men who consumed 2.5 or more eggs per week had an 81% increased risk of lethal prostate cancer compared to men who consumed less than 0.5 eggs per week (HR: 1.81; 95% confidence interval (CI): 1.13, 2.89; p-trend: 0.01)."

Now the first question you have to ask is this. With 27,607 men involved, how did they know how many eggs they ate? And the answer of course is the infamous standard nutritional questionnaire, beloved by nutrition researchers, which is nearly useless for understanding what people really eat.

I've discussed what's wrong with this questionnaire HERE and suggest you read the section headed "1.Based on Inaccurate Questionnaire Data." to better understand the problem here.

In brief, this questionnaire determines how many eggs you've eaten by asking multiple choice questions like "How many eggs did you eat during the past month." The answers you can choose from are very broad along the lines of . "Never, 1-5 times, 6-20 times, more than 21 times."

The chances that the average middle aged man can accurately remember how many eggs he ate during the past month are low, and even if he did, there's a big difference between 6 and 20 eggs which the questionnaire makes it impossible to discover.

But the real problem here is that the way the questions are phrased. In these questionnaires, the subject is asked how many time a day they eat potatoes or bread, but the multiple choice answers assume at least 2 servings a day for each so you would have to say you ate potatoes or bread five or six times a day for the questionnaire software to notice anything odd about your potato or bread intake at all.

But what the questionnaire doesn't ask this: "Did you eat your eggs with toast? "Did you eat your eggs with pancakes and syrup?" "Did you eat your eggs with biscuits?" Or even, "Did you eat your eggs with a large latte?" In fact, it probably doesn't ask about large lattes at all--because one problem with the questionnaire is that the foods it asks about are generic.

Add to this the problem that when a nutritionist thinks of a serving of a food like pancakes, they are thinking of nutritional database values, so the questionnaire does not account for the fact that "one serving" of "pancakes" or "potatoes" at most restaurants today are actually the size of four servings as defined in nutritional databases. So the person reporting that they drank a Latte can only report that they drank "Coffee with sugar," which the software treats as having 8 grams of carbohydrate, rather than as the 66 gram montstrosity the subject drank at Starbucks.

So of course, you can now see where this is going. Men who eat eggs are not eating an egg or two in isolation. Come on guys. I've seen you eat breakfast. And what I've seen is that when a man who is not on a strict diet eats breakfast (and that's 98% of most men) They're eating 2 eggs, ham, bacon or sausage, a big serving of home fries and two slices of toast. If they eat their "egg" at McDonalds or some other fast food outlet, they're very likely having it with a large Coke, or a frappaccino with 88 grams of sugar. They may be having it with a 68 gram Bear Claw from Panera Bread. In short, the egg, which the subject remembers ("I had eggs at Macdonalds) is a marker for a bunch of starch and sugar at goes unnoticed.

We KNOW for a fact that tumors feast on glucose and that high blood sugar promotes the growth of cancers. In constrast, we know of no reason why eating an egg should damage health. Eating dggs, contrary to popular belief, makes no significant difference in people's cholesterol level (not that cholesterol causes cancer, either). Eggs are almost all protein and we know of no connection between eating normal dietary levels of protein. So the real conclusion that should sum up this study should have been this:

In the unlikely case that these questionnaires accurately represent what the men who died of prostate cancer ate, and that the memory of consuming eggs actually correlates with an increase in fatal cancers, this association could be explained by the fact that subjects who consumed eggs ate them in meals containing large amounts of dietary carbohydrate and damaged fats, a circumstance our nutritional questionnaire is incapable of detecting. Remember, too, that association is not causation, and ignore this study until someone comes up with one that uses a better study design.



Natalie said...

Well, what do you think about the fact that Denmark is now going to impose a tax on products that have more than a certain level of saturated fat? It is SO hard to study nutrition, because nutrients simply CANNOT be studied in isolation -- people have to eat SOMETHING! And I really resent scientifically uneducated politicians using scientifically unproven information to punish their constituents!

Jenny said...

The Danish fat tax is definitely misguided. But it's the logical outcome of decades of bad science which has been promulgated by all the major health authorities.