Wednesday, February 28, 2007

The Modern Nutritional Fallacies

I love news days like this. The two top health stories on are about studies that throw into question the legitimacy of two major tenets of mainstream nutritional advice: avoid saturated fat and get lots of antioxidants.

The first study shows that women who ate the most high fat dairy foods were protected from fertility problems whereas women who ate lots of low fat dairy products were as much as 85% more likely to have fertility problems. The second study showed that using the antioxidant supplements Vitamin A, Vitamin E and Beta Carotene certainly does not increase longevity and might actually increase your risk of dying. Whoops!

Here's the most interesting paragraph in the first article:

Intakes of lactose, calcium, phosphorus, and vitamin D were unrelated to anovulatory infertility, the researchers reported. It had been thought that dairy fat and lactose might impair fertility by affecting ovulatory function, they said. However, few studies have been conducted in humans, and the results are inconsistent.

In other words, even though there's no supporting evidence, the prevailing wisdom is that dairy fat is bad for fertility because saturated fat is always bad and lactose is bad because everyone is scared of the dreaded lactose intolerance. Never mind that there's essentially no lactose in yogurt or cheese and that people who are lactose intolerant can tolerate quite a bit of lactose before experiencing any major health problems like flatulence. Turns out the prevailing wisdom is wrong on both counts. That's hardly surprising because, like I said, the prevailing wisdom isn't based on scientific evidence. In nutrition, it seems, even the scientists tend to be more swayed by emotional arguments that they are by hard data.

These papers highlight several of the prevailing fallacies of modern nutritional advice. Let's take a look.

Preferential Citation.

The dominant belief that saturated fat is bad is inevitably tied to the Seven Countries Study, a study that the late Dr. George V. Mann referred to as "a classroom demonstration in naivete" in his scathing 1977 New England Journal of Medicine review, "Diet-Heart: end of an era". There have been many more modern, better controlled studies that have contradicted these findings but yet the seven countries study world view remains the dominant paradigm despite all of its methodological issues (ie, Dr. Ancel Keys hand picked the seven populations. Why didn't he choose any populations in France, Switzerland or Poland?). My current favorite study that refutes the seven countries study findings is Low-carbohydrate-diet score and the risk of coronary heart disease in women.

Incidentally, this one is very insidious, because before too long a preferentially cited paper becomes common knowledge. At this point it is VERY hard to fight, no matter WHAT the data says.

Foods are the sum of their component parts.

The supplement article is more guilty of this, but they're both guilty. No one has ever sat down to a meal of saturated fat. The fallacy works like this. A study comes out showing that people who eat lots of green leafy vegetables have lower rates of heart disease. Scientists say, "Ooh! Look at that! It must be because of the antioxidants/vitamin E/beta carotene/whatever." Experiments are done with supplemental antioxidants/vitamin E/beta carotene/whatever. They fail. It never seems to dawn on American scientists that perhaps the beneficial heart effects lie in the food itself and not some extract of it. For instance, maybe the leafy vegetables are replacing a starchy baked potato or french fries. Maybe the key is the specific proportions of nutrients in the vegetable. Or even more radically, maybe people who eat green leafy vegetables tend to sit down with their families and enjoy an unhurried meal. Additionally, there are lots of components in vegetables that scientists don't even know about - what if the "magic bullet" is one of them. Don't worry, though, scientists won't stop looking for the magic bullet.

Incidentally, if our health officials want us to eat more vegetables, they really need to get off the avoid saturated fat thing. The reason they eat so many vegetables is France is that they cook them with pork fat or butter. Delicious! Last week I hate a cabbage braised in pork fat for dinner. The entire cabbage! How many vegetable servings is that? The recommendations that we should a) eat more veggies and b) steam or boil them are mutually exclusive.

Hypothesis Creep.

The Seven Countries Study led to the hypothesis that saturated fat was a causal agent in heart disease. Then everybody just started applying it to other areas. So the original assumption creeps into the arena of female fertility, "Well, if saturated fat causes heart disease, maybe it also causes infertility." Even if saturated fat did cause heart disease in old men why does it logically follow that it would also cause fertility problems in young women?

You might think that's a bizarre assumption, and you're right. But from the perspective of a researcher, it's a very easy hypothesis to test, your study will get some press because it's about saturated fat, which everyone is interested in, and it might get you a job. And you don't even have know anything about fertility!

The End Result

When scientists and doctors put all of these fallacies together, as they so frequently do, you end up with non-sensical crap like this quote from the first article. I'll leave it to you to find the fallacies from here on out.

Dr Chavarro's advice to women trying to conceive is to change their diet for a while. He said "They should consider changing low-fat dairy foods for high-fat dairy foods; for instance, by swapping skimmed milk for whole milk and eating ice cream, not low fat yoghurt." Once they have become pregnant, then they should probably switch back to low-fat dairy foods as it is easier to limit intake of saturated fat by consuming low-fat dairy foods," said Dr Chavarro.

Can you imagine? Ok, a young woman, we'll call her Sue, goes to the doctor with a fertility problem:

Sue:I can't conceive

Dr. Chavarro:You should eat more full fat dairy products.

Sue:But I thought saturated fat was bad for me.

Dr. Chavarro:It is. So you should stop eating it after you've conceived.

Sue:So you want me to eat something that's bad for me?

Dr. Chavarro:Yes. But don't worry, it will make you more fertile.

Sue:Doesn't that suggest that saturated fat is good for young women?

Dr. Chavarro:No, it just helps you conceive.

Sue:Um... Well..... OK?

Dr. Chavarro:Exactly.