Published 9th April 2020

By Dr Michele Hilton Boon, Research Associate in the Evidence Synthesis team. Michele’s work focuses on health policy evaluation and assessing the certainty of evidence for decision making.

Does taxing unhealthy food and beverages reduce their consumption and lead to better population health? Today our research team published the first of three systematic reviews that aim to answer this question.

After a comprehensive search, we found very limited evidence that a tax on sugar and sugar-added foods can reduce their consumption, but we did not find evidence of a reduction in overweight or obesity.

Obesity is a preventable risk factor for diseases including heart disease, diabetes, osteoarthritis, and some cancers. In 2016, over half of adults worldwide were overweight or obese. In Scotland, obesity also reflects health inequalities, affecting people in the most deprived areas more than those in the least deprived areas. 

Encouraging and enabling people to change their diets and physical activity levels to prevent obesity is a complex problem. From a policy perspective, not only health policies but agriculture, urban planning, transport and education could all contribute to changing our energy intake and expenditure. 

Sugar and sugar-added foods are a major source of excessive caloric intake, which can lead to obesity. The WHO strongly recommends that less than 10% of adults’ daily caloric intake should come from sugars, yet in the UK approximately 17% of our daily calories come from sugars, sugar-added foods, and sugar-sweetened beverages.

Imposing a tax on these foods is one approach governments can take to reduce consumption and prevent obesity in the general population. Indeed, such taxes have been implemented in Norway, Hungary, Denmark, Bermuda, Dominica, St. Vincent and the Grenadines, and the Navajo Nation (USA). Did these taxes work to reduce overweight and obesity or related health outcomes?

In our Cochrane systematic review, we searched 19 databases and screened 18,767 studies to try to answer this question. We wanted primarily to include the types of studies that would provide the best evidence that taxation had a causal effect: randomised controlled trials, controlled before-and-after studies, and interrupted time series. We considered other designs as supporting evidence.

Although taxes on sugar and sugar-added foods have been implemented in several countries, we only identified one study that met our inclusion criteria. An interrupted time series study of the Hungarian public health product tax found that the tax reduced mean consumption of the taxed foods by 4%. We considered this study to provide very low certainty evidence because the data source misclassified the tax status of some food products, and the tax was not solely on sugar but also on salty foods and sugar-sweetened beverages.

In some ways it is disappointing to conduct a comprehensive systematic review and not to find a body of evidence that supports a strong conclusion about the effect of an intervention. However, systematic reviews are also helpful in identifying research gaps, supporting a case for further research, and preventing research waste. We hope that our review will be useful to other researchers, public health bodies, and research funders by showing the need for robust evaluations of the effectiveness of sugar taxes in preventing obesity.

Also, our study is the first of three Cochrane reviews to be published in the next twelve months on the effects of food and beverage taxation on health. Two further reviews will address the taxation of sugar-sweetened beverages and the fat content of foods. The results from the three reviews will provide a clearer picture of the effects of these taxes than one review alone. 

Taxation of unprocessed sugar or sugar-added foods for reducing their consumption and preventing obesity or other adverse health outcomes is fully open-access and available from the Cochrane Library. This review was funded by the UK Medical Research Council, Scottish Government Chief Scientist Office, and the Cochrane Review Support Programme.

First published: 9 April 2020

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