In the US, the Mars bar is a slab of plain (not chocolate) nougat with whole almonds topped with caramel and coated in chocolate. The U.S. Mars bar is not sold overseas.
UK Mars bars
Because of its relatively constant food value (approximately 470 kCal per bar [NK: current UK bar says 280Kcal, Nov 2003]) since its invention, it has sometimes been used as a yardstick of inflation and other economic performance indicators.
For many years the Mars Bar was sold in the United Kingdom using the well-known slogan "A Mars a day helps you work, rest and play".
In 2002 the UK Mars Bar was altered and repackaged to make it more appealing to women. The nougat filling was whipped more, making it lighter and more like the Milky Way. The bar became slightly smaller and the advertising slogan was changed to "Pleasure you can't measure".
The Mars Bar was implicated in a well-known and oft-repeated (but false) rumour involving Rolling Stones vocalist Mick Jagger and his girlfriend Marianne Faithfull. This incident is also thought to have led to the term Mars Bar party as a reference to a sexual orgy.
In 1984 the Mars Bar became the target of a campaign by the animal rights group the Animal Liberation Front, when said group claimed to have contaminated several bars on sale in supermarkets with bleach in protest against the Mars corporation's sponsorship of dental research and tooth decay which involved tests on monkeys. The incident was later revealed to have been a hoax.