"A study … challenged recommendations by public health officials for people to cut sugar consumption," the Mail Online reports. The study has been criticised as it is funded by companies who sell sugary products, including Coca-Cola, PepsiCo and McDonald's.
This systematic review assessed guidelines from all over the world, including those produced by Public Health England. Researchers investigated recommendations on sugar intake and assessed their consistency, the quality of the guidelines, and the quality of the evidence on which the recommendations were based.
The researchers included nine guidelines and found that the development process could be improved and that the dietary sugar recommendations are often based on low-quality evidence. The researchers state that health officials and the public should be aware of these limitations to the existing guidelines.
Caution should be used when interpreting the findings of this research. The study's primary funding source is from the food and drinks industry which has a lot to gain from such findings.
And while the methodology of the review is sound, the researchers fail to point out that when it comes to diet and the impact on health, high-quality evidence is hard to find. The gold standard of evidence-based medicine – randomised trials – are impractical to carry out on large population groups for long periods of time. Public health officials have to work with the available evidence.
Also, the fact that consumption of large quantities of sugar can be damaging to health has been proven without a doubt.
Where did the story come from?
The study was carried out by researchers from institutions including the University of Minnesota and the University of Toronto. This project was funded by the Technical Committee on Dietary Carbohydrates of ILSI North America, which in turn is a body funded by a group of companies.
Some of the members of this group include Coca-Cola, Hershey Foods, Nestle and PepsiCo. Also, one of the authors of the study is a member of the scientific advisory board of Tate & Lyle; described by the New York Times as "one of the world's largest suppliers of high-fructose corn syrup".
The study was published in the peer-reviewed journal Annals of Internal Medicine on an open-access basis so it is free to read online.
There is a very obvious conflict of interest here as many of the members of the funding group are in the food and drinks industry and often come under fire for the sugar content of their products. To be able to conclude that sugar is not as bad as we think would greatly benefit them. However, the authors do state that the study was conducted independently of the funding source.
The Mail Online has been responsible in its reporting on this study, clearly stating in the headline that funding had come from the industry and highlighting the controversy.
What kind of research was this?
This was a systematic review which aimed to review guidelines on sugar intake and assess the consistency of recommendations, the quality of guidelines and the quality of evidence on which recommendations are based.
A systematic review is an excellent way of combining evidence to reach firm conclusions so long as the methods used are robust. However, systematic reviews are only as good as the underlying evidence.
What did the research involve?
The researchers searched three literature databases, guideline registries and grey literature sources (literature not published by commercial sources – such as government reports) to identify any public health guidelines published between 1995 and 2016 that looked at sugar intake for the general population.
They assessed the guidelines using internationally recognised standard quality assessment tools. The Appraisal of Guidelines for Research and Evaluation (AGREE II) instrument for assessing guideline quality and the GRADE (Grading of Recommendations Assessment, Development and Evaluation) methods for assessing the quality of the body of evidence described in articles supporting the recommendations.
The main outcomes of interest to the research team were as follows:
- overall quality of development of the guidelines
- the consistency of sugar recommendations
- the strength of the recommendations
- an assessment of the supporting evidence for each recommendation
- the use of systematic review methods
links between recommendations and supporting evidence
- strengths and limitations of the underlying research evidence
What were the basic results?
Of a potential 5,315 records screened, nine guidelines met the inclusion criteria. One was global, two were international and six were national guidelines. The vast majority of papers were excluded as they were assessed as not providing recommendations on sugar intake for the general population.
The guidelines provided 12 recommendations on dietary sugar intake, all of which stated that intake of free and added sugar should be reduced and that consumption of foods and drinks high in refined sugars should be limited.
Five recommendations provided specific sugar intake limits ranging from less than 5% of total energy from free sugars to less than 25% of total energy from added sugars, suggesting that decreasing sugar intake would reduce excess energy intake, dental caries, weight gain, and obesity.
The quality of the development of the guidelines using the AGREE II assessment method was found to be moderate. The methods for development were not as rigorous as would be expected, with only three guidelines meeting the acceptable level in all domains. Four of the guidelines did not use systematic methods to search for evidence.
How did the researchers interpret the results?
The researchers conclude: "Guidelines on dietary sugar do not meet criteria for trustworthy recommendations and are based on low-quality evidence. Public health officials (when promulgating these recommendations) and their public audience (when considering dietary behaviour) should be aware of these limitations."
Conclusion
This systematic review assessed guidelines from all over the world.
This was an attempt to investigate recommendations on sugar intake and make assessments on their consistency, the quality of guideline development and the quality of the underlying evidence on which the recommendations were based.
The researchers found that the process for developing guidelines on dietary sugar could be improved and recommendations are often based on low-quality evidence. They stated that health officials and the public should be aware of these limitations.
However, caution should be taken when interpreting the findings of this research. The primary funding source for the study is from the food and drinks industry that has a lot to gain by casting doubt on the recommendations in such guidelines.
It is important to consider the validity of the process for developing guidelines separately from the validity of the science linking increased sugar intake with health outcomes. Sometimes decisions for public health need to be based on the available evidence.
The argument that various guidelines were based on evidence judged to be of poor to moderate quality may be an entirely valid point. But it shouldn't be taken as an implication that there is a body of high-quality evidence that contradicts the guidelines.
It is well known that consumption of large quantities of sugar can be damaging to health and increasing the amount of total calories coming from free sugars in food or sugar-sweetened drinks has been associated with:
- higher rates of tooth decay
- weight gain
- higher risk of developing type 2 diabetes
Current recommendations in the UK are that free sugars should not make up more than 5% of the energy you get from food and drink each day. This applies to all age groups from two years upwards. In real terms, this means:
- no more than 19g a day of free sugars for children aged four to six
- no more than 24g a day for seven to 10-year-olds
- no more than 30g a day for children from age 11 and adults
Analysis by Bazian. Edited by NHS Choices. Follow NHS Choices on Twitter. Join the Healthy Evidence forum.
Analysis by 
Edited by NHS Choices