The sugar tax works, and calling it a “sin tax” plays into Boris Johnson’s hands

Shaming people into changing their lifestyle is a lot less effective than nudging them in the right direction.

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“If we want people to lose weight and live healthier lifestyles, we should encourage people to walk, cycle and generally do more exercise. 

“Rather than just taxing people more, we should look at how effective the so-called sin taxes really are, and if they actually change behaviour.” 

These were the statements made by Boris Johnson, the likely future prime minister of the UK, which caused a furore in the media last week. 

The sin tax that Johnson refers to is the sugar levy that has been in place in Britain since last summer. Its two-tier design has promoted many fizzy drink companies to reformulate their products in order to reduce their sugar content. Numerous studies and articles have made clear why Johnson was wrong to call into question the effectiveness of the sugar levy, as noted here, here and here

The study most cited is one that looked at the effects of the sugar tax in Mexico. After just one year, there was a 6 per cent reduction in the consumption of fizzy drinks. Sugar taxes work because they nudge us to make healthier choices. Eating healthily is an individual choice but as Dr Harry Rutter wrote in The Lancet “the range of options within which people make their choices is skewed in favour of weight gain rather than weight loss.” The sugar levy is an attempt to level the playing field. 

The real question is why did Johnson choose to pick on the sugar tax? The sugar levy currently only affects fizzy drinks. In other words, we are all grown adults arguing about whether a can of coke should cost 5p more or not. 

One of the reasons why Johnson’s attack on what he has labelled a “sin tax” works is because we are very bad at accepting the kind of evidence that proves its effectiveness. 

Dr Jane Ogden, a professor in health psychology at the University of Surrey, explains that there are two types of evidence that we value: population evidence and individual evidence. 

While population evidence is provided by those scientific studies showing the sugar levy works, individual evidence is built upon what we see day to day. Ogden says “our personal experience tends to override everything else, and we tend to generalise to everyone else.” So if we see somebody drink a can of coke a day and still be in shape – we think that this must apply to everyone. 

Another reason why Johnson’s comment struck a chord, according to Ogden, is that we generally don’t like to think that we can be controlled; “we think that we can be healthy, so why can’t other people? It’s about a lack of empathy”.

The stigmatisation of overweightness and obesity continues to be an issue in Britain, as proved by the controversy over Cancer Research UK’s ads comparing obesity to smoking. Johnson plays into this “othering” by saying that people should just exercise more. Dr Lou Atkinson, a lecturer in psychology at Aston University, tells me that there’s a perception that those who are overweight or obese are “lazy and don’t care about their health”. 

Atkinson calls out Johnson’s use of the term “sin tax”, saying: “it’s absolutely dreadful. It gives the impression that people are consciously and wilfully being unhealthy. And it makes people feel guilty about the decision that they’re making”. 

Studies also show that making people feel bad about their health is not an effective way of getting them to change their behaviours. If anything, it only makes it worse. 

Obesity is a complex problem with a whole array of solutions needed. The sugar levy is just one small part of that solution. A study published earlier this year by the epidemiology unit at the University of Cambridge looked at the support for and perceived effectiveness of the sugar levy in Britain. 

The study found that while 90 per cent of people understood the link between sugar and obesity, two-thirds still thought of sugary drinks in a positive light. Around 70 per cent of participants believed that the levy would be effective. 

One of the most interesting aspects of the study was the fact that participants were told that the money raised by the levy would be used to fund school breakfast clubs and sports activities. Pell tells me that “previous research has found that people are more supportive of hypothetical taxes on sugary drinks if they’re told the funds will be spent on programmes to support health.” 

When the levy was announced in 2016, George Osbourne stated that the revenue generated would be used to fund both school breakfast clubs and sports activities, and this is still the case today. Yet how many people know this is what the sugar levy is funding? Perhaps if they did, Johnson’s cynical attempt at causing a media storm wouldn’t be so successful. 

Ultimately, Atkinson notes, the entire conversation around “sin taxes” has been extremely successful in one way: “detracting from Boris’s poor record on health as a whole.”

Jason Murugesu is a postgraduate student in science communication at Imperial College London, and a former Wellcome Scholar at the New Statesman.