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It is always frustrating when a public health campaign advances consumer knowledge without having a similar impact on behaviour. A case in point is the 5-a-day campaign to promote fruit and vegetable consumption. In 2000, 43% of consumers were aware of the 5-a-day message and 26% claimed to be putting this into practice (Foods Standards Agency, 2001). Yet, consumption data from the 2000/01 National Diet and Nutrition Survey (NDNS) reported that fewer than 15% of adults met the 5-a-day target (Henderson et al. 2002). Nowadays, 74% of consumers are aware of the 5-a-day target and 58% claim to be putting this into practice (Food Standards Agency, 2008). Assuming a similar embellishment of the intake question, it would appear that the gap between knowledge and action is widening.

 

Given the Department of Health’s strict interpretation of what counts as a portion of fruit and vegetables, it is interesting to speculate whether intakes might improve quicker if the criteria for smoothies were changed. At present, 100% juice and smoothies count as ‘one portion’ no matter how much of either is drunk. The adult NDNS found that average daily consumption of fruit and vegetables, as per 5-a-day criteria[1], was 227g. When all juice and smoothies were counted, this rose by 48g, i.e. an extra half portion per day. This would underestimate current intakes as consumption of smoothies was negligible in 2000.

 

In their systematic review, Ruxton et al. (2006) found that pure fruit and vegetable juices offered similar health benefits to whole fruits and vegetables on account of their high polyphenol content. They argued that there was no justification for the public health view that juices were somehow nutritionally inferior and should be restricted to a single 5-a-day portion. Yet, even if it is accepted that juices and whole fruits confer similar health benefits, concerns remain about the potential impact of juices on sugar consumption, fibre intakes, dental health and appetite control. While these may hinder relaxation of the 5-a-day criteria for juices, it is now time to consider whether such concerns are equally valid for smoothies. In other words, should smoothies be defined as two portions of fruit and vegetables?

 

 

Smoothies are combinations of homogenised fruit and juice. Single servings of commercially-available smoothies contain at least 1 portion of whole crushed fruit (80g) plus 1 portion of juice (150ml), or contain in excess of 80g of whole crushed fruit with the remainder as juice.

 

As Table 2 shows, smoothies contain more energy, carbohydrate, sugars, fibre and vitamin C than juice per 100g. Due to the inclusion of whole, homogenised fruit, smoothies contain 1.7g of fibre per 100ml, compared with 0.1g/100g obtained from juice. Both drinks are rich in vitamin C and could make a labelling ‘source’ claim under Nutrition and Health Claims Regulations (EC 1924/2006). However, only smoothies would be allowed to make a fibre ‘source’ claim.

Unlike juices, the macronutrient composition of smoothies is similar to that found in two portions of fruit. Figure 1 compares an average smoothie with three different banana combinations. It can be seen that energy, carbohydrate, sugar, starch and fibre did not vary across the examples. Notable, is the lack of difference in sugar content (all around 30g) suggesting that the total sugar intake of consumers choosing a smoothie as part of their 5-a-day would not be significantly higher than that of consumers selecting a banana/mango or banana/cherry combination instead.

 

 

While pure juices have been consumed for many years, commercially-available smoothies are a recent phenomenon, although their share of the chilled juice market increases annually. A recent YouGov survey[2] suggested that 37% of consumers occasionally or regularly drank smoothies, while earlier NDNS data showed that 45% of adults and 48% of children drank fruit juice (Gregory et al. 2000).

 

Current average consumption of smoothies is unknown and the category was not mentioned specifically in any of the published NDNS. However, assuming that a 250ml single serving of smoothie were to be consumed, the potential contribution of smoothies to Guideline Daily Amounts (GDA) could be estimated (Table 1). The estimate suggests that smoothies would make a modest contribution to energy, but a potentially important contribution to recommendations for fibre (18% GDA) and vitamin C (>100% Reference Nutrient Intake). Around 29% of the GDA for total sugars would be provided by a portion of smoothie, although none of the sugars are added. A smoothie also provides 18% of the GDA for fibre, superior to the 1% provided by an equivalent portion of freshly squeezed orange juice.

 

 

Health professionals often perceive that juices and smoothies are relatively high in calories and sugar compared with whole fruit, and that consumption should be discouraged in order to prevent a rise in sugar intake. This is an erroneous belief in the case of smoothies which contain around 30g of total sugar per serving, a similar amount to that found in one banana and a portion of mango or cherries. Thus, a consumer exchanging a serving of smoothie for a banana combination equivalent to two portions of fruit would not ‘save’ on calories or sugar.

 

Leading on from this are concerns that smoothie consumption may have a detrimental impact on dental health due to the sugars or pH. The current UK definition of sugars makes a distinction between the supposedly cariogenic non-milk extrinsic sugars (NMES) present in fruit juice/smoothies and the ‘less cariogenic’ intrinsic sugars present in whole fruit (Department of Health, 1989). This would mean, in theory, that consuming a smoothie represented a greater risk to dental health than consuming two portions of whole fruit. However, this is not borne out by the available evidence. Two human clinical studies have compared the dental impact of whole and processed fruit, finding no significant difference as would be expected if NMES and intrinsic sugars were dissimilar in terms of their caries risk. Hussein et al. (1996) looked at plaque pH following consumption of fruits that had been processed or left whole. No significant differences were found between whole, homogenized and juiced fruit, except for minimum pH in oranges which was lower in the juiced version. Issa et al. (personal communications) conducted a similar experiment in human volunteers using in situ enamel slabs; a more precise way of estimating caries risk than plaque pH. Again, there were no significant differences in enamel demineralisation when whole and juiced fruits were compared. A third human study (Beighton et al. 2004) compared saliva samples after whole or pulped fruit was chewed by volunteers. Both forms released equivalent amounts of fruit acids and sugars into the mouth, and stimulated oral bacteria to ferment these sugars into the caries-causing lactic acid. Taken together, these studies suggest that fruit in any form has the potential to adversely affect dental health, and that juices, smoothies and whole fruits pose a similar risk. In practice, there is no evidence that normal consumption of fruit or smoothies increases the risk of dental caries.

 

One of the stated reasons for limiting 100% juice to one portion of 5-a-day was to encourage consumers to eat a variety of produce, rather than obtaining the entire recommended amount from a large carton of juice. Yet, the adult NDNS found that higher consumers of fruit juice were more likely to eat fruit compared with non or low fruit juice consumers. As Figure 2 shows, people drinking more than 200ml fruit juice a day ate 1.8 portions of fruit (excluding the juice), while non-consumers of fruit juice ate only 1 portion of fruit. This suggests that fruit juice is not substituted for whole fruit, but consumed in addition. The adult NDNS also showed that fruit juice consumers were twice as likely as non-consumers to achieve the 5-a-day target. In the absence of comparable data for smoothies, it is not unreasonable to assume a similar scenario. It is also worth noting that, unlike many pure juices, smoothie recipes contain a variety of fruit and vegetable ingredients.

 

The rise in soft drink consumption has led to claims that liquid calories fail to trigger appropriate satiety mechanisms and, thus, could promote weight gain. While the evidence linking sugar-sweetened soft drinks with obesity risk is accumulating, the case for fruit juice is less convincing. The adult NDNS showed that fruit juice consumers were less likely to be overweight than non-consumers. A major difference between juices and smoothies is the latter’s high soluble fibre content (4.3g per serving). Over half of the fibre in smoothies is pectin which has been found to increase satiety (Tiwary et al. 1997). It is, thus, unlikely that moderate smoothie consumption would represent a risk factor for obesity.

 

 

The steady growth of smoothies in the chilled juice market creates an opportunity to help more consumers achieve the 5-a-day target. This will only be possible if smoothies are designated as two portions of fruit, rather than being lumped together with juices as ‘one portion’. Smoothies are significantly higher in fibre, vitamin C and antioxidants than juices and meet the criteria to make a labelling claim for fibre. Smoothie recipes contain at least one 80g portion of mashed fruit plus a juice, and are nutritionally equivalent to two portions of fruit. The sugar content of smoothies does not differ from the equivalent fruits consumed whole. Concerns around the putative influence of smoothies on diet variety, dental health and obesity risk are not borne out by the available evidence. In the case of dental health, it is clear that whole, mashed and juiced fruits present a similar risk in theory. In conclusion, the nutritional benefits offered by smoothies far outweigh any risks, and a re-evaluation of the 5-a-day criteria is justified.

 

 

Beighton D, Brailsford SR, Gilbert SC, Clark DT, Rao S, Wilkins JC, Tarelli E & Homer KA (2004) Intra-oral acid production associated with eating whole or pulped raw fruits. Caries Research 38, 341-9.

Department of Health (1989) Dietary sugars and human disease. Committee on Medical Aspects of Food Policy. London: HM Stationery Office.

Food Standards Agency (2000) Consumer attitudes to food standards. London: Food Standards Agency.

Food Standards Agency (2008) Consumer attitudes to food standards: Wave 8. London: Food Standards Agency.

Gregory J, Lowe S, Bates CJ, Prentice A, Jackson LV, Smithers G, Wenlock R & Farron M (2000) National Diet and Nutrition Survey: young people aged 4 to 18 years. Volume 1: Report of the diet and nutrition survey. London: The Stationery Office.

Henderson L, Gregory J, & Swan G (2002) National Diet and Nutrition Survey: adults aged 19 to 64 years. Volume 1: Types and quantities of foods consumed. London: The Stationery Office.

Hussein I, Pollard MA & Curzon ME (1996) A comparison of the effects of some extrinsic and intrinsic sugars on dental plaque pH. International Journal of Paediatric Dentistry 6, 81-6.

Issa, A., Toumba, KJ, Preston, T, Duggal MS Comparison of the effects of whole and juiced fruits and vegetables on enamel demineralisation in situ. Caries Research in press.

Ruxton CHS, Gardner EJ & Walker D (2006) Can pure fruit and vegetable juices protect against cancer and cardiovascular disease too? A review of the evidence. International Journal of Food Science and Nutrition 57, 249-72.

Tiwary CM, Ward JA & Jackson BA (1997) Effect of Pectin on satiety in healthy US Army adults. Journal of the American College of Nutrition 16, 423-8.