Health campaigners are calling for restrictions on fast food adverts at large sporting events, but would limiting these adverts make any difference to rising levels of obesity?
It is almost impossible to go a day without seeing some form of advertisement, whether plastered across large billboards, interrupting television programmes or personalised adverts online, which track our shopping habits by monitoring the websites we visit.
Latest research suggests that almost a quarter of adults are obese, and campaigners from the Academy of Medical Royal Colleges (AoMRC) say obesity is the "single greatest public health threat in the UK".
They are calling for companies like Coca-Cola and McDonald's to restrict advertising at the Olympics as it "completely sends the wrong message, especially to children", said Prof Terence Stephenson, a spokesman from AoMRC.
During the Olympics, all eyes will be on the competition, but those watching may be inadvertently processing adverts subliminally, according to Prof Nilli Lavie from UCL's Institute of Cognitive Neuroscience.
When watching a sporting event, background adverts will receive little conscious attention, but "the brain will still process them", said Prof Lavie.
Watching a fast-moving event such as a race presents a high level of information load on the brain. Although attention will be on the race "you will still perceive an advert in the periphery of your vision".
"The adverts will only be perceived very briefly but under some circumstances this would subject the viewer to subliminal processing. This means the viewer is not free to choose what they have processed," she added.
A recent survey found that many parents would like to see a complete ban on advertising unhealthy foods before the 21:00 BST watershed. The poll showed parents feel pestered into buying junk food for their children because of adverts.
Cadbury, McDonald's and Coca-Cola are all Olympic 2012 sponsors. "Millions of people are going to see an association between these brands and highly successful athletes. Companies wouldn't spend all this money on adverts if they didn't think it would increase their sales," said Prof Stephenson.
Brands of habit
A spokesperson from Coca-Cola said that it will "increase the marketing budget for our no calorie, zero sugar colas", while a McDonald's spokesperson said that "sponsorship is essential to the successful staging of the Olympics."
McDonald's is also introducing several campaigns focused on "activity toys" and vouchers for sport sessions, aimed at countering criticism of its role.
Linking two stimuli - in the case of the Olympics, a brand to an athlete - is what psychologists call priming. This is where exposure to one stimulus or event in close succession to one another become associated in the mind.
Priming goes hand in hand with familiarity. The more familiar a brand "the more it sinks into our subconscious", said consumer psychologist Dr Sheila Keegan.
As soon as a brand becomes familiar, using its products can become a habit. For a consumer this can represent no longer having a choice, added Dr Keegan.
"A lot of our lives are lived in a semi-automatic way because we cannot process everything going on all the time. Advertisers use this knowledge to encourage people to buy their products without thinking about it too much."
Although there is no specific research on the relationship between fast food adverts at a large sporting event and obesity, Dr Keegan believes such adverts could have a direct impact on the obesity epidemic, especially for people who already regularly eat unhealthy foods, as it becomes "difficult to change that pattern".
Bombarding people with adverts for certain products not only makes individual choice more difficult, but it "builds a society where fast food has become the norm", said Dr Jean Adams, a lecturer in public health at Newcastle University.
Research suggests that children perceive fast food to be less unhealthy when it is associated with sports, added Dr Adams.
And while there are regulations for when celebrities officially endorse a product, in the Olympic arena there will be a constant association between athletes and product brands, something Dr Adams believes "is endorsement at some level".
Prof Stephenson thinks that limiting fast food adverts might work in the same way as the ban on tobacco advertising.
But Martin Dockrell from anti-smoking charity ASH said that while it is known that smoking is extremely harmful, with food it is more about getting the balance right. This could make a ban on fast food adverts almost impossible.
After tobacco adverts were banned, research from ASH found that by 2010, teenage smoking was down to about half the level it had been when the ad ban was passed just eight years earlier.
There are several influences at play, said Dockrell, as the ban coincided with changing social norms and a greater understanding of the harm from tobacco. "It is the combination of many approaches that gives the greatest impact."
Prof Stephenson hopes a similar approach will help tackle the obesity epidemic. People know being overweight is unhealthy but they are struggling to change their behaviour, something he thinks is extremely difficult with the "powerful messages that come through from advertising and branding".
"It is disappointing that the Olympics still feel the need to be sponsored by these companies," he added.