Studies claim that Guinness can be beneficial to the heart. Researchers found that antioxidant compounds in Guinness, similar to those found in certain fruits and vegetables, are responsible for health benefits because they slow down the deposit of harmful cholesterol on the artery walls.
Guinness ran an advertising campaign in the 1920s which stemmed from market research - when people told the company that they felt good after their pint, the slogan was born – "Guinness is Good for You". Guinness were told to stop using the slogan decades ago – and the firm still makes no health claims for the drink. Diageo, the company that now manufactures Guinness, said: "We never make any medical claims for our drinks." The company now runs advertisements that call for "responsible drinking".
Some vegetarians consider Guinness as unsuitable for a vegetarian diet, as the production process involves the use of isinglass, made from fish. It is used as a fining agent for settling out suspended matter in the vat. The isinglass is retained in the floor of the vat but it is possible that minute quantities might be carried over into the beer.