“We hypothesized that the prevalence of obesity would be higher in cannabis users than in nonusers… this analysis showed that even if cannabis consumption increases appetite, people using cannabis are less likely to be obese than people who do not use cannabis…

The authors conclude that the prevalence of obesity is lower in cannabis users than in nonusers.”

http://www.ncbi.nlm.nih.gov/pubmed/21868374
http://aje.oxfordjournals.org/content/174/8/929.long