Juice prepared using a Nutribullet 600 nutrient extractor resulted in a 50% reduction in blood sugar levels compared to whole fruit consumed.
The team from Plymouth University believes this may offer a dietary alternative enabling consumption of normally dietary-restricted fruit juice.
“Even though everyone seems to be using them these days, no one had looked at the effect of fruit juice prepared using a nutrient extractor on blood sugar levels,” said lead study co-author Dr Gail Rees from the School of Biomedical and Healthcare Sciences at the University of Plymouth.
“We were just curious to see how it would compare to the whole fruit.
Blenders homogenize, juicers remove
The increasing popularity of ‘nutrient-extractor’ style blenders in the UK suggests that the public, as well as patients already exhibiting risk factors for Type 2 Diabetes (T2DM), are consuming fruit in a new way for which the health risks remain unclear.
Unlike traditional juicers that remove the pulp leaving only the juice, these blenders homogenize the whole fruit without removing elements such as the fibre-rich skin.
In the crossover design study, each participant served as their own control. Participants were placed in one of two study groups: mixed fruit consumption and mango (high GI fruit) consumption. For each group the two test meals both contained 25 grams (g) total sugar per serving.
For the mixed fruit arm, this consisted of the following: banana (25 g), mango (25 g), passion fruit (50 g), pineapple (50 g), kiwi (50 g) and raspberries (50 g), while for the mango arm it was mango alone (181 g).
Nutrient-extracted servings were processed with 125 millilitres (ml) water. Control meals for both arms were prepared on the morning of testing and consisted of 25 g glucose dissolved in 125 ml water.
Participants consumed each test meal, with a minimum 3-day washout period between test days.
Consumption of nutrient-extracted mixed fruit resulted in a significant lowering of the GI (32.7) compared with whole mixed fruit (66.2).
For the high GI mango, there were no differences between nutrient-extracted and whole fruit, indicating that even for a high GI fruit the effect of nutrient extraction does not increase GI compared with the whole fruit.
“The results were really surprising and we are excited that nutrient-extracted fruit could now possibly be considered a viable alternative to conventional fruit juice for the many people who find it hard to incorporate whole fruit into their diets,” said Dr Rees.
“This is of course only an initial study and will require additional investigation before we know whether this should change nutritional guidelines. Mechanism is also important.”
150ml daily only
Current public health advice in the UK recommends limiting the consumption of fruit juice to just 150ml a day.
The rationale behind this advice stems from the theory that juicing releases sugars from cells, removing insoluble fibre, which in turn increase postprandial glucose response.
In the case of nutrient-extractor-based homogenization, none of the fruit is removed thus both insoluble and soluble fibre remain in solution.
Professor Pete Wilde from the Food and Health Programme, Quadram Institute Bioscience, called for further investigation “to understand how the nutrient extract samples show this remarkable drop in glycemic index (GI) compared to whole fruit in the mixed fruit arm, and why there wasn’t the same drop in the mango arm”.
“The authors suggest that by chewing the whole fruit, it is exposed to salivary amylase for longer than for the nutrient extract, which is presumably drunk more quickly.
”So their suggestion is that less starch is turned to glucose in the nutrient extract, which may lead to slower starch digestion in the duodenum – but this would require further experiments to clarify.
Professor Susan Jebb, professor of diet and population health at the University of Oxford, was critical of the study.
“The study used a standard method to measure the GI of a food but it takes no account of the impact of incorporating blended or intact fruit into the diet in everyday life, for example by measuring glucose levels over a 24 hour period.
“Given the blending seems to have been done in a single batch, any differences would be systematically observed. In both cases, the fruit was frozen and thawed which is not typical for usual consumption and may well affect the GI, so results may not be transferable to usual eating practices.
Source: Nutrition & Diabetes
Published online ahead of print: doi:10.1038/nutd.2017.36
“Nutrient-extraction blender preparation reduces postprandial glucose responses from fruit juice consumption.”
Authors: K M Redfern, V L Cammack, N Sweet, L A Preston, SoBHCS Student Team, M A Jarvis and G A Rees.