Nick Adams/Reuters

PROBLEM: "Marijuana use is associated with an acute increase in caloric intake," goes the clinical jargon for popular lore. Still despite eating more while high (by some measures, over 600 extra calories per day), marijuana users' extra intake doesn't seem to be reflected in increased BMI. Indeed, studies have identified a reduced prevalence of obesity in the pot smoking community.

METHODOLOGY: Researchers at the University of Nebraska, the Harvard School of Public Health, and Beth Israel Deaconess Medical Center analyzed data from a nationally representative sample of over 4,600 adults. About 12 percent of the participants self-identified as current marijuana users, and another 42 percent reported having used the drug in the past. The participants were tested for various measures of blood sugar control: their fasting insulin and glucose levels; insulin resistance; cholesterol levels; and waist circumference.

RESULTS: Current marijuana users had significantly smaller waist circumference than participants who had never used marijuana, even after adjusting for factors like age, sex, tobacco and alcohol use, and physical activity levels. They also had higher levels of HDL ("good cholesterol"). The most significant differences between those who smoked marijuana and those who never or no longer did was that current smokers' insulin levels were reduced by 16 percent and their insulin resistance (a condition in which the body has trouble absorbing glucose from the bloodstream) was reduced by 17 percent.