Naltrexone, an opioid blocker, alters taste perception and nutrient intake in humans

To test the hypothesis that reduced food intake produced by opioid blockade is due to a reduction in the pleasant aspects of tastes, 18 fasted male college students rated the intensity and pleasantness of soup that contained various concentrations of NaCl and of Kool-Aid that contained various concentrations of sucrose at hourly intervals after ingesting either naltrexone (50 mg) or a placebo in a double-blind study. Hunger, fullness, nausea, and current mood state were also assessed. Lunch followed and food intake was recorded. After placebo, the pleasantness of the salted soup increased as lunchtime approached. After naltrexone, however, soup pleasantness remained unchanged across time. Similar changes were obtained for perceived sweetness and pleasantness of Kool-Aid and for the perceived saltiness of soup. Naltrexone also blocked the increases in hunger ratings that occurred across time in the placebo condition. Nausea was higher after naltrexone. After naltrexone, subjects consumed approximately 500 kcal less at lunch than after placebo. Analysis of covariance suggested that decreased hunger (but not nausea or taste pleasantness) accounted for the naltrexone-induced reduction of food intake.