Both brands are preparing major marketing efforts to coincide with their sponsorship of the 2004 Olympic Games in Athens but doctors have expressed concerns that the move will only fuel the spiralling obesity problem.
The view is that the companies should not be allowed to be associated with the sporting event and that organisers should axe them as sponsors.
Dr Ian Campbell, chairman of the government's National Obesity Forum, has said that the companies are using the Olympics to associate themselves with health and activity at the same time as promoting unhelpful sources of calories such as sugary, fizzy drinks and high-fat foods.
McDonald's will have a string of outlets in the athlete's village in Athens and branches outside for spectators. Its global advertising uses the Olympic rings logo, presenting its meals as a good source of energy for those burning off caloroies.
Ads for Coca-Cola will try to persuade consumers that they can share the feelings of global unity created by the games because the drink is available worldwide.
Jude Cohen of London-based charity Weight Concern has called the two companies hypocritical.
"There is something terribly hypocritical about McDonald's and Coca-Cola sponsoring the world's greatest sporting event. There are simply not enough hours in the day for most people to burn off the calories you get from eating fries and a Big Mac," Cohen told the Evening Standard.
McDonald's and Coca-Cola have responded by claiming that they are in fact being socially responsible and offer choice. "It's all about the balance of energy in, energy out," a spokesperson for McDonald's said.
The Olympics Committee maintains that the brands offer choice and that "you can go into McDonald's and order a salad if you want".
One in five Britons is said to be overweight. Two weeks ago the Foods Standards Agency put forward recommendations for a white paper that calls for organisers of sporting events to only accept sponsorship for brands associated with healthier foods. However the proposals are still in early stages and it is not clear whether they will be accepted by government.
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