Both here and in Canada, I have frequently heard Guinness described as “a meal in a glass,” apparently on the basis that it is dark and flavourful. It is a position I have always found dubious, so I’ve decided to do some mythbusting.
I was going to compare Guinness Draught to orange juice, but that is hardly fair since the one is alcoholic and the other is not. Since Guinness is 4.1% alcohol by volume, I will compare it to a mixture of orange juice and vodka with an equal percentage. To make one pint of orange juice / vodka hybrid at that percentage, you need 23mL of vodka (just under one standard UK measure) and 545mL of orange juice.
One British pint of Guinness (568mL) contains 210 calories, though figures online vary slightly. 545mL of orange juice has about 250 calories. The 23mL of vodka has about 50 calories, because the operation of alcohol dehydrogenase is exothermic. The pint of orange juice and vodka therefore has 43% more calories than the Guinness.
Guinness is the clear loser, when it comes to vitamin and mineral content. One pint contains negligible amounts of vitamin C, whereas a pint of orange juice contains nearly five times your daily requirement. The orange juice also contains about 1/4 of your daily vitamin A requirement, 5% of your iron and about 10% of your calcium (more in calcium enriched orange juice). A pint of Guinness does contain 1.6g of protein, so it does have that leg up on the alternative presented. Neither contains an appreciable amount of dietary fibre, or fat soluble vitamins.
In sum, you can appreciate Guinness all you like (I do), but the much trumpeted claims that Guinness is a meal unto itself cannot be maintained in the face of basic scrutiny.