Marijuana causes activation of the cannabinoid receptors and affects tissues involved in energy metabolism, such as the liver and pancreas. Through this activation of receptors, marijuana can affect the regulation of appetite, lipids, and beta-cell function. Short-term marijuana use has been shown to increase food intake and cause glucose intolerance. Despite this evidence, previous research did not study the effect of metabolism with long-term habitual use.
Recently, a new study was conducted to observe the effects of long-term marijuana use on metabolic effects. Thirty participants were enrolled in the study and smoked an average of 10 joints per day for 12 years. There were 30 controls that matched the marijuana users in age, sex, race, and BMI. African-American men were the predominant ethnicity in this study and most of the marijuana users also smoked tobacco. To assess calorie consumption, a 24-hour dietary questionnaire was used to log specific types of foods and calories coming from fats and carbohydrates. The marijuana group consumed more calories as carbohydrates and was rated to have a poorer quality of diet on the Healthy Eating Index Scale compared to the controls.
A magnetic resonance imaging machine measured the total and subcutaneous (SQ) abdominal fat by users and non-users. The machine showed marijuana users having lower percentages of total and SQ abdominal fat. Users and controls had similar fasting glucose and insulin levels. HDL cholesterol was lower in users, however, no differences were seen in LDL, triglyerides, or free fatty acids. Also, the readings of CRP, leptin, adiponectin, incretins, and liver transaminases were similar between the controls and users.
The results of the study showed that there was no effect on surrogate insulin sensitivity measures related to glucose metabolism compared with the controls. These surrogate measures included quantitative insulin sensitivity check index, oral glucose insulin sensitivity, and hepatic insulin resistance. In addition, they found no impairment in beta-cell glucose sensitivity or rate sensitivity in the user group. The authors concluded, "In healthy young individuals, chronic cannabis smoking was associated with visceral adiposity and adipose tissue insulin resistance but not with hepatic steatosis, insulin insensitivity, impaired pancreatic beta-cell function, or glucose intolerance."
Muniyappa R, et al "Metabolic effects of chronic cannabis smoking" Diabetes Care 2013; DOI: 10.2337/dc12-2303.