The association between pot smoking and lower risk of obesity remained strong even after adjusting for other factors that could influence body fat and health, such as cigarette smoking, age and gender. But the correlation between weed and weight doesn’t mean that marijuana smoking actually causes weight loss.
Many other factors could account for the connection. For example, some research finds that highly religious people are less likely to take drugs, but more likely to be obese — perhaps because they’re substituting one compulsive behavior (overeating) for the other (smoking marijuana). So, some of the obese people in the national surveys may be religious folk, who might otherwise be heavy marijuana smokers, but are eating too much instead. That could make it look like marijuana is slimming.