The obvious connection between durian, the big smelly spiky Asian fruit, and the Shangri-La Diet is that both rely on flavor-calorie learning. We come to like the initially unpleasant smell and flavor of durian because we learn to associate it with the calories in the fruit. Here’s what happens

“To anyone who doesn’t like durian it smells like a bunch of dead cats,” said Bob Halliday, a food writer in based Bangkok. “But as you get to appreciate durian, the smell is not offensive at all. It’s attractive.

From an article in today’s New York Times. The theory that led me to the SLD centers on flavor-calorie learning.

A less obvious connection is a principle that helped me discover that drinking sugar water causes weight loss. I was in Paris and lost my appetite — a rare event. The principle is that rare events are usually due to rare events. So I wondered what else unusual had happened. Well, there was something: I had been drinking several sugar-sweetened unfamiliar soft drinks per day. When I got back to Berkeley I started to test the possibility that sugar-sweetened water can cause weight loss and SLD was born.

For a fruit, durian has three rare properties:

1. very strong, unpleasant smell

2. very big

3. hard to handle (because spiky)

Following the Rare-Causes-Rare principle, these should have a common explanation. Lightning does not strike thrice in one place for different reasons. According to Wikipedia,

The thorny armored covering of the fruit may have evolved because it discourages smaller animals, since larger animals are more likely to transport the seeds far from the parent tree.

That’s a good explanation of #3 and it explains the other two rare features (#1 and #2) as well. The reason for the strong smell (#1) is so that the signal will be broadcast a long distance: Large animals are less dense than small animals. We think of the smell of ripe durian as very unpleasant but perhaps almost all unfamiliar smells are unpleasant; so any random strong smell will seem very unpleasant. Big fruit (#2) means big tree and big tree means that seeds must be carried far away so as to be placed in soil where they will not compete with the mother tree. Coconuts are big and hard to eat. Pineapples are big and spiky.

The Rare-Causes-Rare principle also helped me discover the effect of morning faces on my mood and the effect of omega-3 on my balance .