We have recently had a number of conversations about fruit and sugars, particularly glucose spikes caused by eating fruit. But should we be concerned about enjoying fruit as a smoothie beverage, where the whole fruit is blended?
We have discussed the evidence regarding glucose spikes and the health effects of whole fruit and fruit juice in another article, here. Below we share the latest research on blended fruit.
As ever, please talk to your doctor, or medical practitioner most familiar with your medical history before implementing any changes in diet, exercise or lifestyle; especially if you are under treatment. We provide links to the quoted studies at bottom of page.
What do Studies on Blended Fruit vs Whole Fruit Show?
Crummet and Grooso, 2022 demonstrate"This study showed that consuming apples and blackberries that have been processed in a blender yields a reduced postprandial glycemic response compared to consuming them in whole form, as measured by glucose maximum, glucose iAUC, and 60 min glucose. The trend that we observed may be associated with the fact that we used a seeded fruit (blackberries with seeds included) that was added to a non-seeded fruit (apples with seeds removed), given the results from two other studies.
Redfern et al. reported that blended mango did not have a significantly different glycemic index compared to whole mango in healthy subjects, but blended “mixed” fruit that contained mango, banana, passion fruit, pineapple, kiwi, and raspberries had a significantly lower glycemic index compared to whole mixed fruit.
In a follow-up study by Alkutbe et al., involving obese and non-obese subjects, they showed that consuming blended mango plus a seeded fruit (passion fruit or raspberries) significantly lowered the glycemic index (GI) compared to consuming whole mango plus a whole seeded fruit. Alkutbe et al. postulate that grinding the seeds in the passion fruit and raspberries, during the blending process, may have released fiber, polyphenols, fats and proteins, which may reduce the rate of gastric emptying and glucose absorption in the small intestine."
Also to note, the study authors state: "Ultimately, our results should not be extrapolated to commercial fruit smoothies, which typically use apple juice, sorbet, or ice cream as the base, rather than water. We used water in our smoothie to control the amount of glucose present in blended fruit vs. whole fruit treatments. Adding juice or ice cream to a fruit smoothie would significantly increases the sugar content of the smoothie, without increasing fiber content, which would increase glycemic response. Haber et al. reported that apple juice yielded a significantly larger insulin response than either blended apples or whole apples, and thus, adding apple juice to smoothies may not be a healthy choice."
Another study, this time the above mentioned Redfern et al, 2017 showed that "Results from our study indicated that nutrient extraction of fruit has the potential to significantly lower its GI. Notably, the effect of nutrient extraction resulted in a lowered GI response even than consumption of the corresponding whole fruit, with whole fruit being associated with a medium GI between 55 and 69, whereas the nutrient-extracted fruit juice had a low GI ⩽55.11
Although the mango arm of our study did not follow the same pattern, nutrient-extracted preparation of the mango juice did not adversely influence GI compared with whole fruit, with both preparations exhibiting a low GI.
These finding may have important clinical implications for healthy people, as well as T2DM patients, who are currently following recommendations to avoid fruit juice in the hope of improving glycemic control. Low GI diets have been shown to improve body weight, glycemic control and glycated hemoglobin levels."
Food Order and Glucose Spikes
A current trend in online media is a discussion, verging on fear, around glucose spikes when eating food and fruit. 'Spike' is a potentially frightening name for an entirely normal biological response to consuming carbohydrates. For most of the population, this sudden increase and decline in glucose - shown as a sharp peak when measuring and visualising blood glucose data - is entirely normal and healthy. This is how the body is meant to react. When the increase in blood sugar does not return to normal (within say 2 hours), this indicates a potential problem as the sugar struggles to be cleared from the blood. It is when your blood sugar is consistently too high that it can put you at a higher risk of chronic conditions e.g. heart disease and type 2 diabetes. Here we have seen that blended fruits, still with their fibre and polyphenols, remain a healthy option.
Interestingly, when the effect of food order is mentioned, in 2023 a 16 week randomised controlled trial by Shukla et al set out to investigate the effect of changing the order that food is eaten has on health. In the study of pre-diabetic and healthy participants they found that contrary to their hypothesis, food order - irrespective whether the participants ate vegetables, carbs or protein first in the meal - made no meaningful difference over time. Glucose tolerance was unchanged in both groups after 16 weeks. Changes in weight, HbA1c were also similar between the groups. They did however find that those who ate their vegetables first ended up eating more vegetables.
The natural sugars in fresh fruit, bound with fibre and polyphenol anti-oxidants, are processed differently by the body compared to added sugars in processed foods. Perhaps counter-intuitively, the data shows that blended fruit is not the problem that many thought it might be. However, fruit juices which are higher in concentrated sugars have a different effect on blood sugar levels.
Don't fear fruit, embrace it as part of a balanced diet.
Want to take your smoothie to the next level? Add some nuts and seeds, add some spices. Healthy fats, satiating protein, additional polyphenols and micronutrients all support better health outcomes. One thing to consider, it is a lot easier to consume liquid calories than food in its whole form - food that requires chewing.
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Stay Healthy,
Alastair
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Related Studies and Resources
Crummett LT, Grosso RJ. Postprandial Glycemic Response to Whole Fruit versus Blended Fruit in Healthy, Young Adults. Nutrients. 2022 Oct 30;14(21):4565. doi: 10.3390/nu14214565. PMID: 36364827; PMCID: PMC9657402.
Alkutbe R, Redfern K, Jarvis M, Rees G. Nutrient Extraction Lowers Postprandial Glucose Response of Fruit in Adults with Obesity as well as Healthy Weight Adults. Nutrients. 2020 Mar 14;12(3):766. doi: 10.3390/nu12030766. PMID: 32183321; PMCID: PMC7146348.
Redfern KM, Cammack VL, Sweet N, Preston LA; SoBHCS Student Team; Jarvis MA, Rees GA. Nutrient-extraction blender preparation reduces postprandial glucose responses from fruit juice consumption. Nutr Diabetes. 2017 Oct 9;7(10):e288. doi: 10.1038/nutd.2017.36. PMID: 28991222; PMCID: PMC5678208.
Haber GB, Heaton KW, Murphy D, Burroughs LF. Depletion and disruption of dietary fibre. Effects on satiety, plasma-glucose, and serum-insulin. Lancet. 1977 Oct 1;2(8040):679-82. doi: 10.1016/s0140-6736(77)90494-9. PMID: 71495.
Other
Wang DD, Li Y, Bhupathiraju SN, Rosner BA, Sun Q, Giovannucci EL, Rimm EB, Manson JE, Willett WC, Stampfer MJ, Hu FB. Fruit and Vegetable Intake and Mortality: Results From 2 Prospective Cohort Studies of US Men and Women and a Meta-Analysis of 26 Cohort Studies. Circulation. 2021 Apr 27;143(17):1642-1654. doi: 10.1161/CIRCULATIONAHA.120.048996. Epub 2021 Mar 1. PMID: 33641343; PMCID: PMC8084888.
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