Though cannabis use is often associated with unmitigated sloth and gluttony, a new study suggests the opposite: cannabis use may be associated with a decrease in obesity. An analysis of over 20 years of data found that obesity dropped by a significant margin in states where medical cannabis is legal. Though the researchers’ findings represented correlation as opposed to causation, the results, like many new findings about cannabis, chip away at decades-old stereotypes about the plant and its users.
The study, titled “The Effect of Medical Marijuana Laws on Body Weight,” was published in Health Economics, an academic journal that focuses on health policy and services, health care sciences and services, and economics. Researchers from Cornell University’s Department of Policy Analysis and Management and San Diego State University’s Department of Economics analyzed data from the Center for Disease Control’s Behavioral Risk Factor Surveillance System. The BRFSS is the “premier system of health-related telephone surveys that collect state data about U.S. residents regarding their health-related risk behaviors, chronic health conditions, and use of preventive services,” according to the CDC.
The researchers studied data from 1990-2012 — gleaned from over five million individual survey responses — in what they call the first ever study to “examine the effects of medical marijuana laws (MMLs) on body weight, physical wellness, and exercise.” They used a “difference to difference” approach, a method in which researchers use ‘before and after’ data in one group and analyze it alongside “a comparison group that is experiencing the same trends but is not exposed to the policy change.”
Though the study acknowledged that previous randomized control studies found cannabis was associated with increased appetite and caloric intake, their findings determined that “the enforcement of MMLs [medical marijuana laws] is associated with a 2% to 6% decline in the probability of obesity.”
The researchers presented different explanations of the trend for different age groups and posited that among older individuals, cannabis use is often used to treat chronic pain. They hypothesized that with reductions in pain come increased physical activity, and as a result, lower rates of obesity.
The study’s authors offered an alternative analysis for adults aged 18-24, suggesting the availability of cannabis is associated with reductions in alcohol consumption. “Our findings show that the enactment of MMLs is associated with a 3.1 percent reduction in the probability of alcohol consumption and a 4.8 percent reduction in the probability of binge drinking,” they explained. Alcohol is high in calories, and compared to cannabis, which has zero calories, the difference is substantial. When cannabis is more accessible, the authors reasoned, it can “cause substitution toward lower-calorie recreational ‘highs’ among younger individuals.”
The study also suggested that over the long term, results may be even more pronounced. Further, they suggested the apparent reduction in obesity associated with cannabis use leads to lower healthcare costs. “We estimate a back-of-the-envelope-per-person reduction in MML-induced obesity related medical costs of $58 to $115 per year,” they wrote.
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The findings were not without mitigating factors. The Washington Post noted that while some studies have found states with legalized cannabis also see decreased alcohol consumption, other studies indicate alcohol intake actually increases in MML-friendly states, leaving conclusions on the matter murky.
Rosalie Pacula, director of the BING Center for Health Economics at the RAND Corp., argued that the Behavioral Risk Factor Surveillance System is not particularly accurate in determining state-level effects, though she did not explain why. She also noted that cannabis legalization is relatively new, and ongoing consequences of such policies are still evolving.
“These data aren’t going to provide us with the definitive answer because of the issues with the data and time period being evaluated,” Pacula told the Post in an email. “Thus, I believe that these findings should be interpreted very cautiously – as they could plausibly be reversed in the future, when other analyses are done using data sets that contain either (a) state representative populations over time, or (b) longer time periods for later policies.”
Though the study has caveats, the findings echo similar studies on related issues. One 2013 study linked cannabis use to a lower risk of developing diabetes, finding cannabis helps control blood sugar. Murray Mittleman, an associate professor of medicine at Harvard Medical School and lead author of that study, explained that the “most important finding is that current users of marijuana appeared to have better carbohydrate metabolism than nonusers. Their fasting insulin levels were lower, and they appeared to be less resistant to the insulin produced by their body to maintain a normal blood-sugar level.”
In reporting on the study, Time noted additional studies that determined “marijuana users are less likely to be obese, have a lower risk for diabetes and have lower body-mass-index measurements. And these trends occurred despite the fact that they seemed to take in more calories.”
Though the findings of the new study must be replicated and further explored to be confirmed, they shed light on as-yet-unknown benefits of cannabis legalization, a policy voters increasingly embrace — and for increasingly good reasons.