The Oral Health Effects of Juices and Smoothies
© Juliette Reeves 2010 

Health Benefits

The driving force behind the fruit juice and smoothie revolution appears to be attributed to the health benefits associated with the consumption of fruits and vegetables in the diet. Smoothies are increasingly being seen as a meal replacement , many see them as an entire healthy meal in a glass.  They are considered by some to be the ultimate fast food.  

Healthy eating, and in particular the 5 a day fruit and vegetable campaign, has been given increasingly more publicity from government policy makers, particularly in light of growing concerns about obesity in adults and children.   The health benefits of increased fruit and vegetable intake are well established (2).  Recent research shows significant health benefits from an increase in antioxidant intake and fruit and vegetable consumption, ranging from improved bone density (3),  cardiovascular and coronary heart disease (4,5) to lung function(6), ageing(7) and mortality rates (8).

 

Oral Health Benefits

The oral health benefits of increased antioxidant intake are also significant. Recent research has suggested that vitamin C deficiency may contribute to the severity of periodontal breakdown(9). Likewise, findings indicated that oral health was better in a zinc rich diet than in zinc-deficiency(10). Study also suggests that increased lipid peroxidation and total antioxidant status may play an important role in the pathology of periodontitis(11).    

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Oral Cancer 

There is a large body of  evidence showing  that an increase in fruit and vegetable consumption is related to a lower incidence of oral cancer. Recent study suggests that patients treated for early-stage oral cavity carcinoma, at risk for second primary cancers, have a statistically significant deficiency in dietary  sources of antioxidant nutrients when compared with both historic control subjects and current recommendations.(12)  More recent studies have shown how additional foodstuffs and micronutrients are also indicated in oral cancer incidence and prevention.  There is evidence that the consumption of cereals, fruits, dairy products, and added lipids (mostly olive oil) was found to be associated inversely with the risk of oral carcinoma (13). Other recent studies concur with these findings.  Frequent consumption of fish, eggs, raw green vegetables, cruciferous vegetables, carrots, pulses,  and overall consumption of vegetables and fruit decreased oral cancer risk (14).  

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Dental Health and Nutrition Concerns 

The consumption of fruit juices and smoothies is often seen as an effective way to increase fruit and vegetable intake, particularly in children. However, what can easily be overlooked is the sugar content and acidic nature of some fruit juices and smoothie combinations. The sugar content of some commercially available smoothies ranges from 20g to 35g per 250mls, more than a can of cola. The British Dental Health Foundation has recently expressed concern over the high sugar content of smoothies, particularly those that contain banana as a base.  

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The  National Diet and Nutrition Survey (NDNS) (15) of young people revealed that 53% of young people aged 4 to 18 years had evidence of dental caries in their primary or permanent dentition. Of particular concern was the finding that over half of the young people examined were considered to have evidence of erosion in the upper incisors or in the first molars of either the primary or the permanent dentition.  

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The mean daily consumption of sugary foods for children aged 4 to 6 years was 473g and 553g from 7 to 10 years.  One in seven young people reported having a drink in bed every night. Between 2% and 4% had a drink in bed every night that contained non-milk extrinsic sugars and between 3% and 6% had a drink every night which was acidic.  

Of additional concern is that some manufacturers make misleading claims about the nutritional contribution smoothies make to the diet. Some claim that their products provide two of the five recommended daily fruit portions, whilst guidelines issued by both the Department of Health and World Health Organisation state that fruit juices and smoothies should count as a maximum of two .

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Many are made from concentrated juices. Fruit juice made from concentrate has been reconstituted with water. Generally, concentrates are more likely to be made from bruised or damaged fruit which tends to have lower levels of vitamin C. Those sold at ambient or room temperature contain fewer additives or sweeteners but the pasteurising process that allows it to be stored at room temperature destroys many of the nutrients. The addition of sugar and water to concentrated fruit juice often reduces the nutritional value even further.

 

Managing Caries and Erosion 

The reported incidence of tooth erosion has been increasingly documented and linked with consumption of acidic food and drinks. Whilst these factors are often  linked, many individuals with erosive diets do not present with erosion. This would suggest the presence of many variables, such as age, mouth clearance and saliva flow and quality. Enamel erosion and softening are based on chemical processes which could be influenced by additional factors including temperature and acid flow rate.  

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Since the rate of chemical reactions usually increases with temperature, it has been predicted that erosion is more severe at high temperatures and reduced at low temperatures. The results  of a recent study investigating the correlation between enamel softening, enamel erosion, and temperature, showed that material loss increased, and nanohardness decreased, linearly with temperature (16).  

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A number of other studies have also demonstrated the effect of temperature on the rate of enamel erosion (17,18). These studies were able to demonstrate increased enamel erosion and surface loss with an increase in temperature.   These factors could be employed in order to reduce the erosive effect of juices and smoothies. Serving them at lower temperatures, over ice for example, could reduce the risk of enamel erosion.  

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Calcium as a Buffer 

The erosive potential of beverages does not depend on pH alone (19,20). Drinking through a straw lessens contact time with the enamel than drinking from a cup (21). In addition other components of beverages such as calcium and phosphates may act as a buffer to the acid content and increase remineralisation (22). Lewinstein et al (23) demonstrated enamel “re-hardening” greater than salivary stimulation alone on softened enamel when cheese, cheese-flavored with strawberry jam, and  sucrose-sweetened cheese were consumed. In addition Jensen and Donly (24) were able to demonstrate similar results using whole and semi skimmed milk.  

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Consuming milk base smoothies or juices increases calcium and phosphate content and may reduce the risk of erosion and enamel demineralization. For those who may be lactose intolerant, calcium enriched Soya or oat milks would have the same effect. Nut milks such as almond milk also contain a high concentration of calcium and phosphate. Ground almonds blended with water or added to a smoothie is a useful alternative to milk.  

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Dental Health Guidelines 

There are a number of simple guidelines which would allow our patients to consume fruit juices and smoothies and gain the health benefits without compromising their dental health.  

Home made juices and smoothies are preferable to commercially produced products as the sugar and fruit acid content can be controlled or modified. The frequency of consumption should also be limited to one 250ml portion per day, in line with Department of Health recommendations. This is primarily due to the lack of insoluble fibre available in fruit juices. This should be consumed in one sitting, rather than sipped over a prolonged period of time. For young children the size of the serving should be considerably less. Most 250ml servings contain the juice of 3-4 portions of fruit, much more than a child would normally consume in one sitting. Juices and smoothies should not be given in bottles or drinking cups for consumption over a prolonged period.

 

For the adult population choosing vegetable juices over fruit is also beneficial, as the antioxidant, vitamin and mineral content of  vegetables is also substantial, without the sugar and acidic content of fruit. Restricting the use of fruits with high sugar content and low pH values and using avocados instead of bananas is also beneficial.  Avocados contain vitamins, minerals and essential fatty acids and give a thick starchy consistency without the sticky sugar content found in bananas.  

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Conclusion

As dental health professionals we are in a prime position to give nutritional advice. Popular health and eating fads will at times conflict with dental health recommendations. By examining carefully the basis of a particular healthy eating claim and offering tooth friendly alternatives, we can encourage our patients to adopt a balanced approach to healthy eating without compromising their dental health.

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References

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[1] Mintel Report: Smoothies UK, October 2008

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24 Jensen M, Donly K : Assessment of the Effect of Selected Snack Foods on the Remineralization/Demineralization of Enamel and Dentin. JCDP 2000 ; 1 (No. 3) pp1-12