Acai berries grow on tropical palm trees native to South America. The demand for acai berries reaches beyond that geographical zone, however, due to the fruits' excellent antioxidant and nutrient properties. Fresh acai berries are relatively low in calories, with a range of about 80 to 250 in a 100-gram serving, depending on how the berries are prepared and whether they have been deseeded or not, and a 100-gram serving of pure acai puree has 80 calories. Acai products and supplements often have even lower calorie counts but may contain very little actual acai.
Acai berries are perishable, so they're normally only available in regions outside of South America in the form of juices or powdered supplements. An 8-ounce cup of a commercial acai berry juice drink has about 110 calories, and an 8-gram serving of a powdered acai vitamin C supplement has about 20 calories. Supplements and flavored products may contain little to no actual acai berries, however.