Seth's Blog

In the late 1800s in the United States, babies started developing scurvy; there was a veritable plague. It turned out that the vast majority of victims were being fed milk that had been heat treated (as suggested by Pasteur) to control bacterial disease. Pasteurization was effective against bacteria, but it destroyed the Vitamin C.

From a history of nutrition. Now children are probably getting all sorts of immune disorders, such as hay fever, for the same core reason: fear of bacteria.

Here is a nice review of the hygiene hypothesis, proposed in 1989 by David Strachan. The hygiene hypothesis is that the increases in childhood allergies and asthma in rich countries were due to decreases in “infection in early childhood, transmitted by contact with unhygenic older siblings or acquired prenatally.” It was inspired by the observation that allergies and asthma were less common in larger families.

In the original, it was infections that were the crucial thing you got from older siblings. This idea ran into trouble when actual measurements of number infections did not show the expected inverse correlation:

When a composite index of exposure was generated by combining histories of illness due to measles, mumps, rubella, varicella, and pertussis, the tendency was for a slightly higher risk of allergic disease in children with multiple infections.

Also bad for the infection idea is that vaccination for measles didn’t protect against hay fever or eczema.

It looks to my perhaps-biassed eyes that it is dirt (= harmless foreign proteins and bacteria) exposure that matters, not exposure to human infectious agents. Living on a farm helps. Plainly you get dirty living on a farm and exposed to animal viruses and bacteria — but that you get human infectious agents from pigs and cows is unlikely. (In technical terms, they aren’t vectors.) Older brothers are more protective than older sisters. Boys are dirtier than girls; it isn’t obvious they are more infectious. Dogs are more protective than cats. Again, dogs are obviously dirtier than cats but the notion that they are more infectious — few infectious agents cross the species barrier — is less obvious.

An emphasis on dirt rather than human-infectious agents is more compatible with my belief in the vast importance of ingesting bacteria-laden food.

Track stuff you care about, such as your weight, here. They call it “personal analytics”.

Thanks to Alex Tabarrok.

Karina Smirnoff, a world-champion dancer on Dancing With the Stars, told Us Weekly that she controls her weight by “taking a tablespoon of olive oil on an empty stomach,” which is her mom’s advice. “On an empty stomach” — I wish I’d thought of that way of putting the between-meal requirement. Good Morning America mentions it here — quick, go to the “keeping bodies ballroom ready” segment, which will only be available for a few days.

SLD hasn’t been translated into Russian. A case of independent discovery?

Thanks to Joyce Cohen.

Continuing the theme that wiping out bacteria — as antibiotics do — might be a bad thing, here is a mysterious development:

The new study arose from a mysterious affliction of pregnant cats. A company testing the effects on growth and development in cats using diets that had been irradiated reported that some cats developed severe neurological dysfunction, including movement disorders, vision loss and paralysis. Taken off the diet, the cats recovered slowly, but eventually all lost functions were restored.

“After being on the diet for three to four months, the pregnant cats started to develop progressive neurological disease,” says Duncan, a professor of medical sciences at the UW-Madison School of Veterinary Medicine and an authority on demyelinating diseases. “Cats put back on a normal diet recovered. It’s a very puzzling demyelinating disease.”

Do Americans have bacteriophobia? I believe we need to eat plenty of bacteria-rich food for best health (the umami hypothesis). If so, then irradiating food is like taking all the vitamins out of it. Of course, food irradiation is big business. From a list of FAQs:

4. Does eating irradiated food present long-term health risks?

No. Federal government and other scientists reviewed several hundred studies on the effects of food irradiation before reaching conclusions about the general safety of the treatment. In order to make recommendations specifically about poultry irradiation, U.S. Food and Drug Administration scientists reviewed findings from additional relevant studies.

Independent scientific committees in Denmark, Sweden, United Kingdom and Canada also have reaffirmed the safety of food irradiation. In addition, food irradiation has received official international endorsement from the World Health Organizations and the International Atomic Energy Agency.

The International Atomic Energy Agency. It’s an interesting methodological question: Is Diet X (irradiated food) “safe” because it is no worse than Diet Y (ordinary food)? What if Diet Y isn’t safe?

Duncan, the researcher quoted above, said this:

“We think it is extremely unlikely that [irradiated food] could become a human health problem,” Duncan explains. ”We think [what happened to the cats] is species specific.”

Hmm. If you don’t understand what causes the effect, how can you make strong claims about it? I think food with too-few bacteria is already a human health problem.

Thanks to Peter Spero.