Question: how many calories does xenical block?
Answer: The active ingredient in Alli is orlistat, which is found in a higher dose in the prescription diet drug Xenical. Alli blocks about 25% of the fat you eat; Xenical blocks one-third of the fat you ingest. For instance, a half-cup serving of Haagen-Dazs ice cream has about 320 calories and 19 grams of fat.