According to a recent Reuters press release, a study in the American Journal of Epidemiology reports that people who frequently smoke are LESS likely to be obese than those who do not smoke. Wow! Man. Although I personally have never inhaled, I have heard rumors that reefer directly and immediately increases the craving for chocolate brownies, Ben 'n Jerry's ice cream, potato chips, pizza, and other highly fattening foods.

The finding is actually a lovely demonstration of a principle we try to teach students in introductory psychology every day: Correlation does not demonstrate causation. Although the researchers were surprised at the negative relationship, I'm not (of course, I have the advantage of hindsight). People I know who have inhaled cannabis fumes are also more likely to hike, to bike, and to walk than are my straighter friends (the ones who listen to Merle Haggard's classic "We don't smoke marijuana in Muskogee"). The pot-smokers are more likely to shop at the local hippie co-op, where they buy organic vegetables, fruits, yogurt, and nuts, and less likely to frequent the local McDonald's. Psych Today had a set of blogs on healthy eating, and one of them listed the top five foods for losing weight: yogurt, nuts, fruits, whole grains, and vegetables. If you eat a lot of those five things, are you more or less likely to have smoked pot?

I'd guess more. And it's not just my biased sample of observations leading me to that conclusion. A few years back, my colleague Ed Sadalla did a study of the links between people's eating habits, dress styles, and drug-abuse patterns. The group that was more likely to eat health foods and vegetables was also more likely to take recreational drugs. Wow, Man!

Doug Kenrick is author of Sex, Murder, and the Meaning of Life: A psychologist investigates how evolution, , and complexity are revolutionizing our understanding of human nature. He had his insights about the "meaning of life" part after hiking through the nearby woods, eating a lot of yogurt and nuts, and listening to Jimi Hendrix.

For a related blog on pot and causality, see "Is opposition to pot-smoking really just fear of sex?"

P.S. A commentator pointed out that I might be stereotyping. The Sadalla research was in line with my stereotypes, though it's several decades ago. There are certainly lots of people who smoke pot who fit into other groups - young kids who listen to various forms of avant-garde music, for example. But stereotypes often have a grain of truth, so I'd ask: Have things changed so that the next generation of liberal hippie types at the organic co-op are now less likely to have smoked pot than the rest of the population? In fact, the more recent research by Kurzban and Weeden (see the link above - "Is opposition to pot-smoking really just fear of sex?" ) suggests that there is still an association between being conservative and opposition to pot-smoking. In all of this, it's important to keep in mind not only that correlation does not imply causation, but also that a correlation between two variables (unless it's 1.0) leaves lots of room for other variables to be involved.