PERSPECTIVES WITH DR ALAN BARCLAY

Juiced? 
We have been juicing fruits for a long time. Here’s a short summary. Wine is fermented grape juice – the fermentation process is a way of preserving the fruit– and it looks like we’ve been making it for about 8000 years. Archeologists have found that the people living at Gadachrili Gora and a nearby village 20 miles south of Tbilisi, Georgia, were the world’s earliest known vintners—producing wine on a large scale as early as 6000BC. Now skip a few millenia. Lemonade became popular in the 1500s, and orange juice in the 1700s and we preserved them by adding sugar (sucrose) which in the right amount inhibits bacterial growth (a good thing). Louis Pasteur’s pasteurization process (1864) preceded the development of fresh (unfermented) 100% fruit juices in 1868. In 1930, the first commercial juicing machine was invented and around this time electric refrigeration became affordable. Home juicing became popular in the USA in the 1970s, thanks to affordable home juicers.

Today, people enjoy 100% fruit juice worldwide and it’s a nutritious choice as the analysis of commercial unsweetened orange juice shows. (And if you are wondering why orange juice rates five stars while a whole orange picked straight from the tree only rates 4½, it’s because Australia’s star rating system currently uses different algorithms for solid foods and for beverages)

The American Dietary Guidelines consider 1 cup (240ml) of 100% fruit juice as being equivalent to one serve of fruit, but they also recommend that at least half our recommended serves of fruit should come from whole fruit, which generally contains more dietary fibre and less calories.

What about the sugars? The carbohydrate in fruit and fruit juice is in the form of sugars (fructose, glucose and sucrose principally). Some people point out that fruit juices can provide nearly as much sugars as some sugar sweetened beverages, which nutrition epidemiological studies have associated with weight gain and risk of type 2 diabetes. Do 100% fruit juices pose the same risk? Fortunately, there is now a relatively large body of evidence that can help answer this important question.

Auerbach and colleagues investigated the association of 100% juice consumption with body mass index (BMI) in prospective cohort studies of children. The overall conclusion was that while consumption of 100% fruit juice is associated with a small amount of weight gain in children ages 1 to 6 years, the amount is not clinically significant. (Controlling for total energy intake, they reported that one 180–240ml (6–8oz) serve of 100% fruit juice a day is associated with a 0.087 unit increase in BMI in children aged 1 to 6 years, but not in children aged 7 to 18 years.) Similarly, systematic reviews of the evidence in adults show no detrimental effects of consuming moderate amounts of 100% fruit juice.

Murphy and colleagues investigated the effect of 100% fruit juice on blood glucose and insulin levels in randomised controlled trials which included a range of people including those who were overweight/obese and/or had diabetes. They found that 100% fruit juice had no significant effect on fasting blood glucose, fasting blood insulin or HbA1c. The overall conclusion was that 100% fruit juices have a neutral effect of on glycemic control, and they noted that these findings were consistent with findings from observational studies suggesting that consumption of 100% fruit juice is not associated with increased risk of developing type 2 diabetes.

Sugars (e.g., glucose, fructose and sucrose) and other fermentable carbohydrates (i.e. maltodextrins and starches), provide food for oral bacteria, which lower our plaque and salivary pH, and in turn promote tooth demineralization. This is the main reason why the World Health Organisation recommends we limit our consumption of free sugars to less than 10% of energy – 100% fruit juices are a source of free sugars. However, most of the studies that make up the evidence base for the WHO guideline are based on added sugars – not juices. So, what does the evidence say about 100% fruit juice?

A recent clinical trial by Issa and colleagues found that a range of solid and juiced fruits (e.g. apples, oranges, grapes and tomatoes) could contribute to tooth demineralisation, but there were no significant differences between solid and juiced foods. A review by Touger-Decker and van Loveren found that many factors in addition to free sugars affect the risk of tooth decay, including the form of food or fluid, the duration of exposure, nutrient composition, sequence of eating, salivary flow, presence of buffers, and your personal oral hygiene. In particular, they noted that polyphenols such as tannins in cocoa, coffee, tea, and many fruit juices may reduce the cariogenic potential of foods and drinks. In addition, in a series of experiments in young adults that included fruits and juices (e.g. apples/juice, dates, bananas, orange juice, raisins), Edgar and colleagues found that while juices had a higher acidic potential than whole fruits, they only moderately increased risk compared to sugar-sweetened beverages and confectionery, which conferred a high risk. In summary, 100% fruit juices are not as likely to cause tooth decay as sugar-sweetened beverages or confectionery.

So, overall, the evidence we currently have supports the American Dietary Guidelines allowance of up to 1 cup of 100% juice a day as part of a healthy balanced diet.

 
Alan Barclay, PhD is a consultant dietitian. He worked for Diabetes Australia (NSW) from 1998–2014 . He is author/co-author of more than 30 scientific publications, and author/co-author of  The good Carbs Cookbook (Murdoch Books), Reversing Diabetes (Murdoch Books), The Low GI Diet: Managing Type 2 Diabetes (Hachette Australia) and The Ultimate Guide to Sugars and Sweeteners (The Experiment, New York).

Contact: You can follow him on Twitter or check out his website.