Young people who watch one extra junk-food advert a week (over the average of six) consume an additional 350 calories in foods high in salt, sugar, and fat (HFSS) every week (18,000 each year), according to the largest study of its kind in the UK involving over 3,300 teens aged 11 to 19 years.
The study conducted by Cancer Research UK, and being presented at this year's European Congress on Obesity (ECO) in Vienna, Austria (23-26 May), is one of the first to look at online TV viewing in such a systematic fashion, and adds to the growing evidence that TV and streaming adverts can influence young people's unhealthy diet.
The take home message is that "junk food marketing is associated with obesity in young people of all ages, and we know that obesity is linked to at least 13 types of cancer", says Dr Jyotsna Vohra, head of the Cancer Policy Research Centre at Cancer Research UK who led the research. Levels of obesity in teens aged between 12 and 19 years tripled in the USA (5% to 17.6%) between 1980 and 2008. Similarly, in England, around a fifth of children in the last year of primary school (aged 10 to 11), and one in every four adults is obese. Obese children are around five times more likely to become obese adults with a much higher risk of health problems including 13 obesity-related cancers, type 2 diabetes, and cardiovascular disease.
Although the causes of obesity are complex, previous research has found strong links between increases in advertising for fast foods and rates of childhood overweight and obesity. An earlier Cancer Research UK study, also being presented at ECO, showed that teens who report 3 or more hours of commercial screen time (television or streaming) a day are twice as likely to consume large amounts of foods HFSS compared to those who watch less than 3 hours a day.
Regularly eating high calorie food and drink--which usually has higher levels of fat and sugar- increases the risk of becoming overweight or obese. An obese child is more likely to remain obese into adulthood, putting them at risk of cancer, which is the biggest preventable risk after smoking in the UK for the disease.
In this study, Dr Vohra and her Cancer Research UK colleagues investigated the link between HFSS food marketing and unhealthy food and soft drink consumption behaviours among teens in the UK. They started by conducting a qualitative scoping study to explore young people's perceptions of marketing, and the mechanisms linking this with dietary choices. They went on to survey a national sample of 3,348 young people aged 11 to 19 years to further examine the link between marketing and high calorie diets. Participants were asked about their age, gender, ethnicity, socioeconomic status, food and drink consumption, TV and online viewing habits, what HFSS adverts they remembered, brand awareness, and reactions to HFSS ads.
On average, young people watched 21 hours of television a week with adverts, with just over half of this time viewed on streaming platforms. However, obese participants watched significantly more television--around 26 hours (equivalent to one extra advert a week).
On average, young people reported eating almost 30 HFSS food items every week (equivalent to 40-50% of this age group's recommended total calorie intake), but only 16 portions of fruit or vegetables.
Overall, results showed that the more junk food ads young people watched, the more HFSS foods they were eating. All participants were able to recall a favourite HFSS television advert, and were particularly influenced by adverts that were fun, targeted, age appropriate or catchy.
The researchers found that greater familiarity with fast-food marketing was associated with eating more foods HFSS and increased weight, regardless of age and gender. However, those from a more deprived background were more likely to recall HFSS adverts than those who were not. "This combined with their already greater risk of unhealthy weight outcomes suggests that young people from deprived backgrounds would potentially have the most to gain from regulation designed to reduce junk food ad exposure", explains Dr Vohra. Over 40% of participants said they felt pressured to eat unhealthily, and 80% of the 10 food and drink brands young people recalled most frequently had at least one HFSS product in their top sellers.
The authors conclude: "The food industry wouldn't pump hundreds of millions into advertising their products by creating catchy adverts if it didn't get people to eat more. Broadcast regulations in the UK haven't been updated since 2008, and our research shows that the current restrictions clearly aren't working. With today's teens spending more time in front of screens than any other activity apart from sleeping, curbing exposure to junk food ads on streaming platforms as well as TV will be key to helping teens make healthy diet choices and reducing obesity rates."
In 2017, a report by the Obesity Health Alliance found that junk food companies in the UK spend almost 30 times more on advertising (£143 million) than the Government does on healthy eating campaigns (£5 million).
The authors acknowledge that their findings show observational differences rather than evidence of cause and effect. They note some limitations, including that the study is based on a self-reported survey of viewing and eating habits which can lead to problems of recall and could have affected the results.