Guinness is also lower in calories than the average beer, even though it has a richer mouthfeel and fills you up. Alcohol is the main source of calories in any alcoholic beverage, so a Guinness will naturally be lower in calories than a Budweiser containing 5% alcohol—even though it might seem more filling.
The Foreign Extra Stout is Guinness' strongest beer at 7.5 percent alcohol by volume.