American-style fast-food restaurants are part of the fabric of modern life in Saudi Arabia, the world's biggest oil exporter with a mostly affluent population of about 24 million.
Statistics released at a Health Ministry conference on Saturday indicated that obesity affected 51% of Saudi women and 45% of men, as well as 29% of teenage girls and 36% of boys.
The government says there is a specific danger to children, who can now make use of special telephone help lines.
Health experts say a spiralling increase in diabetes and other illnesses among Gulf Arabs has been the price of a rapid modernisation of their desert states.
Most nationals of the wealthy oil producing region have switched to a Western-style sedentary life from a physically demanding nomadic existence over the last 50 years.
Weigh your life
The new campaign to eat more healthily and exercise - "Weigh your life" - has been launched in the Saudi media with the help of prominent public figures who have had noted battles against weight gain.
Turki al-Dakhil, a television presenter, said: "There is desire to eat and there is appetite for food and they are two different things. It is the desire that is the problem and you have to use your mind to get over it."
Al-Dakhil was promoting a book, Memoirs of a Former Fatty, which catalogues his life as a 185kg (408-lb) media personality who had to book two seats for himself on international flights to the United States. He is now less than 100kg.
Hamad al-Mani, the health minister, wrote in an article: "The overweight face the task of changing some eating habits and spending less time in front of the television and computers. A lack of physical exercise is making it worse,"
However, Saudi primary and secondary schools do not allow physical education for girls because of opposition from hard-line clerics who consider it inappropriate for women.