The effect of whole and blended fruits on blood glucose levels Original paper

Compared to eating whole fruit, drinking fruit juice seems to increase glucose levels to a greater extent, perhaps because fruit juice lacks the fiber found in whole fruit, which can slow absorption of the sugars.

A common way of consuming fruits is by blending them into smoothies. In blended form, the fiber is retained, but the fruit’s cellular structure is broken, which may increase the speed at which the sugars are absorbed. Do blended fruits increase glucose levels more than whole fruits?

This acute (short-term) randomized controlled trial assigned 20 healthy college students (average age of 20) to consume apple (190 grams; central core and seeds removed) and blackberries (148 grams), either whole or blended with water and ice. To control for water intake, the whole-fruit group also drank the amount of water provided by the blended smoothie. The participants consumed the fruit 3–4 hours after eating lunch.

Glucose levels, including maximum glucose level, glucose area under the curve (AUC; the total rise in glucose during the time), and glucose incremental area under the curve (iAUC; AUC adjusted for baseline glucose levels), were assessed in the 60-minute period after consuming the fruit.

Compared to whole fruit, blended fruit resulted in a lower maximum glucose level and lower glucose AUC. The blended fruit also resulted in a lower iAUC, but this finding was not statistically significant (p=0.057).

The authors speculated that the blended fruit reduced glucose levels compared to whole fruit because the blending process causes a greater release and dispersion of compounds like fiber and polyphenols from the fruit matrix compared to chewing. Because these compounds may inhibit glucose absorption, this could have attenuated the glucose response.