Confusing correlation with causation

One of my pet peeves with scientific journalism is the propensity to confuse correlation with causation. The idea is that just because two things are observed to happen at the same time (or before, or after, one another), does not imply that one causes the other.

In the latest example of this, the link between chocolate and good health is revisited.

The article opens with:

People who eat chocolate regularly tend to be thinner, new research suggests.

… which implies that a causation has been observed. The article goes on to make the following points:

[…] those who ate chocolate a few times a week were, on average, slimmer than those who ate it occasionally.

The link remained even when other factors, like how much exercise individuals did, were taken into account.

[…] it is how often you eat chocolate that is important, rather than how much of it you eat. The study found no link with quantity consumed.

So… I’d still lose weight if I ate a tonne of chocolate very frequently? Really?!

The most important statement, however, comes a little later:

But the findings only suggest a link - not proof that one factor causes the other.

… and,

And if you are looking to change your diet, you are likely to benefit most from eating more fresh fruits and vegetables.

Now guess what the headline of this article, which itself says that it’s only a link, and talks about maintaining an overall good diet, reads.

Chocolate ‘may help keep people slim’

Perfect, isn’t it?

Tapeworms inside the human brain

Most of us have heard of tapeworms, the parasitic creatures that find their way into the human digestive system, and can grow very long indeed. They can cause quite a bit of trouble, but I had no idea how extreme the trouble can sometimes be.

Theodore Nash sees only a few dozen patients a year in his clinic at the National Institutes of Health in Bethesda, Maryland. That’s pretty small as medical practices go, but what his patients lack in number they make up for in the intensity of their symptoms. Some fall into comas. Some are paralyzed down one side of their body. Others can’t walk a straight line. Still others come to Nash partially blind, or with so much fluid in their brain that they need shunts implanted to relieve the pressure. Some lose the ability to speak; many fall into violent seizures.

Underneath this panoply of symptoms is the same cause, captured in the MRI scans that Nash takes of his patients’ brains. Each brain contains one or more whitish blobs. You might guess that these are tumors. But Nash knows the blobs are not made of the patient’s own cells. They are tapeworms. Aliens.

This is scary—they can find their way into the bloodstream, and in the human brain, where they happily live and grow as cysts.

Well, let’s back up a bit. I didn’t know that the tape worm life cycle involves humans and pigs, and that the normal life cycle can only be completed via undercooked pig meat. There you go, I thought, that’s why you should avoid undercooked meat.

But—no. That’s not the half of it.

The more serious trouble (of the brain cyst kind) happens when the normal tapeworm cycle is disrupted. Instead of finding their way inside a pig, tapeworm eggs sometimes find their way straight back inside humans, and the confused eggs behave as they would in a pig—reach for the blood stream. And that’s the recipe for disaster. You could be having tapeworm cysts in your brain, without ever having had raw or undercooked meat.

I won’t give everything away; go read the whole article. It’s excellent, informative, and as I said, a little scary.

☛ Of the brain-eating amoeba

Be careful what you do with your tap water:

The Louisiana Department of Health and Hospitals has issued a weird warning: if you have to irrigate your sinuses with water for some medical reason, don’t use tap water. The reason: your brains may get eaten by the Naegleria fowleri.

Water that you drink is quite all right—even if it contains the bacteria, it will be destroyed when it reaches the stomach and the body’s digestive juices.

But beware if you intend to put water up your nose! This channel is not intended for water (or other food), and does not have the same defense systems as our digestive system does.

The amoeba attacks your nervous system, and can pretty soon leave you dead! Fortunately, the way around is pretty simple: just boil the water to kill the bug!

(My gripe with the article: no source information! No links, whatsoever. Terrible.)

Forks over Knives’

I recently found this very interesting documentary, called ‘Forks over Knives’, that deals with the idea that much of our modern health problems can be solved by changing our diets. This in itself is, of course, not a revolutionary idea—most of us are quite aware of what we need to do to stay healthy. (That we don’t actually do it is another matter entirely!)

What piqued my interest (and great dismay) was some of the views in the documentary—were some of the ideas that I currently have so wrong? And the theses were from respected doctors, who seemed to have done quite a bit of research, and extensive research at that, in coming up with their ideas!

Some of the ideas that I already had, before watching this movie:

  • Processed foods are worse than ‘natural’ foods
  • Veggies and fish are ‘healthier’ than platefuls of red meat.
  • Refined sugars are certainly pretty bad
  • Fast foods are certainly bad.
  • Balanced diets, based on veggies, small portions of meat and fish, and dairy products are good.

With this background, I was dismayed to hear that:

  • ANY animal proteins are apparently bad
  • Even milk is bad!
  • Plant based diets” are the way to go (no animal foods)
  • Animal proteins can cause cancer (and tumors)!
  • … and other ‘facts’ along these lines.

While I’m no dietician, and have no background in nutrition sciences, my senses were troubled because of the following:

The movie’s point of view veers extremely close to the textbook definition of “being a vegan”. No animal products, period. They chose to use the less controversial “plant based diet”, but the idea is pretty much the same. This is not a problem in itself, but–

I don’t think “vegan” diets are natural to homo sapiens (i.e. evolutionarily consistent). Historically, evolutionarily, it seems to me extremely unlikely that we’d have adapted to using nothing from animals in our diets. Indeed, most sources caution that “careful planning”[1,2,3] is needed to ensure that all nutrients are present in a vegan diet—it’s apparently easy to miss out especially on the essential Vitamin B12 if you’re not mindful.

It seems much more natural that given our hunting-gathering backgrounds, we’d much rather be the omnivores that most of us are—eating whatever we found (and hunted down), and being extremely pleased with such a diet. I’m perfectly comfortable with “vegetarian” diets that add milk and other dairy products, but I found it dubious that simply coming from animals made certain foods harmful.

And so I looked it up, and came across this extremely detailed critique of the movie–well, at least the science in the movie. And after a few minutes of glancing through the article, I’m a little more relieved—according to this author, the movie does gloss over certain additional information that would be helpful, and does sometimes mistake correlation for causation.

And it does overstate the harmful effects of animal products on our health, sometimes going to the length of being inaccurate.

As of now, my takeaway is this: certainly watch the movie—it’s a nice overview of the effect of a balanced diet and nutrition on our bodies. But remember the word “balanced” more than the words “plant based diet”. Also, read through the blog article above for a thorough discussion, after you watch the movie.

Do you know of other sources of information that either support or detract from the ideas in the movie (and the blog)? Can you point to relevant research?