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Dental benefits of sugar-free foods debated

“Sugar-free gum, sweets and soft drinks, marketed as healthy alternatives to sugary products, can damage teeth, cause gastric problems and are unlikely to promote weight loss,” The Guardian has reported.

The news is based on a review of the oral health effects of sugar-free products, and in particular, a group of sweeteners called polyols that are often added to sweets, drinks and chewing gum. It is already well known that dental cavities can be formed when bacteria convert sugars in food into acid, which breaks down tooth enamel. However, in this new study, researchers looked for evidence on whether foods containing certain sugar substitutes were beneficial for dental health.

While the researchers found some evidence that cavity formation was inhibited by certain polyols, in particular the ‘tooth-kind’ sweetener xlylitol, they say they could not find clear evidence on whether tooth enamel was damaged by sugar-free foods and beverages containing acidic flavourings and preservatives alongside polyols.

The research has highlighted that there is a lack of data on the potential actions of foods containing certain sweeteners, in particular how they compare to full-sugar products. However, until this evidence is gathered, people can still protect their teeth against the established causes of tooth decay by maintaining good oral hygiene (brushing and flossing regularly) and eating less sugary foods.

Where did the story come from?

The study was carried out by researchers from the University of Helsinki in Finland, Boston University and the University of Southern Nevada in the US. The authors did not declare any sources of funding. The study was published in the peer-reviewed British Dental Journal.

This story was covered by The Guardian, Daily Express and Daily Mail. Newspapers have tended to overstate some of the statements featured in the original study paper, which found that a lack of evidence meant that we could not be sure that sugar-free products were not damaging to teeth.

For example, The Mail reported that ‘sugar-free treats are every bit as dangerous for teeth as sweet ones’. However, the research paper reported that ‘in general, sugar-free products may help prevent dental caries’ but might increase the probability of demineralising tooth enamel if they contained acidic additives.

The Guardian said that sugar-free products are ‘unlikely to promote weight loss’, but the research paper just says that ‘sugar free does not mean calorie free’ and that some sugar-free products generate less than 50% of the calories produced by table sugar.

This does not mean that sugar-free sweeteners do not provide a lower-calorie alternative to sugar, just that the calorie reduction from replacing sugar with sweeteners may not be as large as some might assume, particularly as some people might assume that sugar-free sweeteners are calorie-free.

The Guardian also reported that polyols ‘cause acidity in the mouth that then leads to erosion of teeth enamel’, where the research paper mainly concentrated on the acidity levels of the additives and preservatives used alongside sweeteners in sugar-free products.

What kind of research was this?

This was a narrative review looking at the oral health effects of polyols and sugar-free items. The researchers also performed a systematic search of research papers to identify where there was relevant research, and where a lack of research made it difficult to judge the effects specific sweeteners had upon teeth. Although the researchers gathered study papers systematically the authors do not describe how they chose the particular studies they included in their review.

Dental cavities are one of the most common health issues today, affecting a large proportion of the global population. Cavities form when bacteria convert sugars in food and drink into acid, which breaks down tooth enamel. Tooth decay can therefore be prevented by reducing intake of sugars and by reducing the amount of the acid-forming bacteria in the mouth through good oral hygiene (brushing and flossing regularly).

In order to reduce the amount of sugar people consume manufacturers have begun using various types of sugar substitutes to create number of sugar-free products. In this study, researchers have examined and discussed data on one group of popular sugar substitutes called ‘sugar alcohol polyols’, which are often used to sweeten chewing gum, sweets, foods and drinks.

Polyols have predominantly been used to manufacture food for diabetics, as polyols are not readily absorbed in the intestine, and therefore reduce changes in blood glucose levels after eating. However, although polyols have reduced calorific value compared to sugar, they are not calorie free. Furthermore, because polyols are not absorbed well by the intestine, they may accumulate and cause gastro-intestinal disturbances such as diarrhoea.

This was an appropriate study design to address this question. However, as the authors note, there has been a lack of randomised controlled trials in this area, and this means they could only produce a descriptive review of the limited body of evidence available.

What did the research involve?

The authors searched several medical literature databases using the search terms ‘sugar alcohol’, ‘sugar-free’ or ‘polyols’ in combination with the search terms ‘dental caries’ or ‘dental erosion’. They searched for all evidence published up to the end of October 2010 and produced a descriptive review of the available evidence. Although the research gathered study papers systematically, the authors do not describe how they chose the particular studies they included in their review.

What were the basic results?

The researchers say that one particular polyol, xylitol, has been mainly investigated as a component of chewing gum. It has been approved by the US Food and Drug Administration (FDA) for its ability to reduce risk of dental decay. Recently, the European Union also officially approved xylitol as a ‘tooth friendly’ component of chewing gums. The researchers point out that xylitol has been studied extensively in clinical trials and predominately found to be effective.

The researchers say that xylitol in chewing gum has three properties that allow it to reduce the risk of dental decay:

  • it is not fermented into acid by oral bacteria
  • it can limit the number of bacteria in the mouth by limiting the amount of fermentable sugar that bacteria can feed on
  • it can induce the production of salivary enzymes, which inhibit bacterial growth

However, the researchers say that another polyol called sorbitol is often used for sweetening sugar-free products such as chewing gum as it is cheaper than xylitol. Unlike xylitol, sorbitol can be fermented into acid by some bacteria, and therefore should not be considered to have the same cavity-inhibiting effects. They also highlight that to date there have only been a few clinical trials looking at the cavity-inhibiting effects of sorbitol.

In addition, the researchers point out there may be a hidden risk in sugar-free products. Acidic flavourings and preservatives may have adverse dental health effects, including dental erosion. They say the effects of acids in sugar-free products have yet to be directly studied, but it is already established that the additives in sugar-free products reduced the pH of saliva and therefore may weaken tooth enamel.

How did the researchers interpret the results?

The researchers conclude that ‘polyol-based sugar-free products may decrease dental caries incidence’. However, they may present a ‘dental health risk’ if they contain acidic flavourings. The researchers add that there is a need for properly conducted clinical studies in this area.

The researchers also suggest the term ‘sugar free’ may generate a false sense of security because people may automatically believe that sugar-free products are safe for teeth.

Conclusion

It is well-established fact that dental cavities can form when bacteria convert sugars into acid, which then breaks down tooth enamel. It is also well established that tooth decay can be reduced by reducing the amount of the acid-forming bacteria in the mouth by maintaining good oral hygiene (brushing and flossing regularly), and by reducing intake of the sugars that they feed off.

This new research paper has highlighted the potential of dental corrosion from sugar-free food and drink products, which the authors say can be down to the additives, preservatives and sweeteners they contain.

In particular, the researchers have examined evidence on the various sugar substitutes that have come into use in recent years and how they are widely used in sugar-free items. They say that several studies have shown that the sugar substitutes polyols (especially xylitol) reduce or even prevent dental cavities, but that there has been little research into the overall cavity-promoting effect that sugar-free confections containing these substances may have.

Although there is a lack of evidence on these products it is already known that some of the additives they contain can themselves reduce the pH of saliva, making it more acidic, and therefore may be a potential source of dental erosion. Overall, it does seem that there is need for more research into the effect sugar-free products have on dental health.

That said, without this further research, it should not be assumed that these products definitely do erode teeth in a major way. The results of this review have highlighted that at present there is a lack of randomised trials that might confirm whether or not these products truly do have an effect.

Overall, this study has highlighted an important area for further investigation but cannot tell us how erosive sugar-free food and drinks are or whether they are any better or worse than products containing sugar, which may also contain acidic preservatives and flavourings.

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