There is a huge problem with epidemiological studies that propose ‘relationships’ between foods and health outcomes. All of the statisticians and scientists are fully aware of the problems with the ‘correlations’ that these studies expose, but they still draw those conclusions, they still cite the studies when trying to recommend policy changes to the government. Here are the known problems with epidemiology:
Selection bias is one of three types of bias that can threaten the validity of a study. Selection bias occurs when study subjects are selected or become part of the study as a result of a third, unmeasured variable which is associated with both the exposure and outcome of interest. For instance, it has repeatedly been noted that cigarette smokers and non smokers tend to differ in their study participation rates. (Sackett D cites the example of Seltzer et al., in which 85% of non smokers and 67% of smokers returned mailed questionnaires.) It is important to note that such a difference in response will not lead to bias if it is not also associated with a systematic difference in outcome between the two response groups.
Information bias is bias arising from systematic error in the assessment of a variable. An example of this is recall bias. A typical example is again provided by Sackett in his discussion of a study examining the effect of specific exposures on fetal health: “in questioning mothers whose recent pregnancies had ended in fetal death or malformation (cases) and a matched group of mothers whose pregnancies ended normally (controls) it was found that 28% of the former, but only 20% of the latter, reported exposure to drugs which could not be substantiated either in earlier prospective interviews or in other health records”. In this example, recall bias probably occurred as a result of women who had had miscarriages having an apparent tendency to better recall and therefore report previous exposures.
Confounding has traditionally been defined as bias arising from the co-occurrence or mixing of effects of extraneous factors, referred to as confounders, with the main effect(s) of interest.
Most nutritions studies suffer from every one of these defects. Study participants are selected out of a community that is already sick, for instance has already had a cardiac event. Study participants may be different in many ways from the general public. For instance, when studying the effects of the Mediterranean diet they might only have people who are already very health conscious join the study. Confounding is hard to compensate for because finding a correlation that is a single cause is impossible in people where you cannot control or catalog every bite of food they take.
Yet, despite this, the government, with no better data to go on, makes dietary recommendations to a sick and sickening public. Even though their scientists know that the data are not conclusive, they fear that making no recommendation will cause more problems than making a premature recommendation. At least that was how they thought back in the 70s and 80s. Now that we have all been Guinea pigs for forty years, eating low fat and high carb like the government recommended–now that we are all fat and getting fatter, sick and getting sicker–the government is free to change the recommendation, and to admit the flaws.
The bad thing is that the government doesn’t do that explicitly. Their once-every-five-years recommendations still contain a caution about meat and fats. The justification changed, but not the recommendation. Now we shouldn’t eat meats and fat because it’s bad for the environment. Well, actually, industrially produced meats are bad for the environment because eighty percent of all the grain grown for food is fed to livestock to fatten them up. It turns out that the ill effect on the environment is that. If you can find someone to sell you meat that is not raised on grains like corn and soy then there is nothing wrong with eating meat and fat.
This distinction is lost on dietitians and doctors, though. My mother just left the hospital after a cardiac event and the diet advice she got was “low fat”, “low cholesterol”, which is the same old advice. She should be hearing that she needs to eat way less carbs, and that if she wants to reduce her carb intake by eating local meats that would be the best course, going forward. I knew she was going to get this bad old advice and I warned her. I don’t know whether my non-professional opinion will carry as much weight as a doctor in a lab coat who has had very close to zero formal training on diet or nutrition, but we will see.
People get sick when they eat too much sugar and starch over a long period of time. If you eat margarine instead of butter you are probably harming your heart. Eating unnatural foods with unnatural ingredients is risky. Eating processed foods, with their added sugars and lowered fats is risky. Eating the Western diet is risky. Nobody is sounding the alarm though that has a big enough bullhorn to get everyone’s attention. Our government is not even likely to warn us even if there is an illegal ingredient in foods. (See yesterday’s post for this news). Money and profit are trumping every other consideration, including Federal law.
You are really and truly on your own these days. Science has been coopted by industry. Your government is being coopted by industry. Look to foreign lands for honest advice about what you should eat and what you should avoid. When Canada bans something, you should quit eating it. When the European Union restricts something, you restrict it, too. Someday our nation might, but it could be decades before it happens. Real science is being performed in the world, but it’s just not around here. Real government is being enjoyed somewhere in the world, but its just not in the USA.