It was somewhere between cutting up my second kiwi and throwing a handful of ice into the blender that R decided to tell me about the research he’d read on the negative impact that blending has on the nutritional value of fruit; specifically that it increases its GI and, in his words, ‘basically makes it fattier’.
Having committed to my super-green and ginger smoothie by this point I’d be damned if I was going to bin the lot, besides, my cold had been lingering and I wanted the vitamin c boost of the kiwis, but I have to be honest, it didn’t taste quite as virtuous with R’s words still ringing in my ears.
So, as a big smoothie and juice fan I decided to do some research of my own.
It is perhaps unsurprising to hear that the process of blending fruit reduces its satiety levels, while also leading you to consume more fruit than you would normally do in solid form. It is far too easy to drink a couple of kiwis, a banana and a satsuma when blended up, (as I did), and still manage a whole bowl of porridge on top, whereas you would certainly think twice about chomping down the whole lot unblended.
Psychologically, it is much more satisfying to chew and crunch food, rather than to drink it. This act of chewing is the first part of digestion and it is this that starts the release of digestive enzymes, preparing your body for food and telling you that you have begun eating.
Crunch factor aside, smoothies also have a lower satiety level due to the changes in the structure of the fibre in the fruit and the release of sugars that occur when blending. While you may think that if you put an apple into a blender wholesale the fibre content remains much the same before and after blending, in fact the fibre is so finely pureed that its beneficial properties (including the fact that it makes you feel full) are all but lost. What is more, the breakdown of the fruit also results in the sugars being released more quickly, impacting on your blood sugar and insulin levels, giving you the sugar spike and subsequent dip that can make you feel hungry again almost immediately afterward.
In one study comparing calorie intake at a meal following the consumption of an apple, applesauce, apple juice with fibre added and apple juice with no fibre added, the results showed a rather telling story.
In those instances when the subject ate a whole apple before the meal their calorie intake decreased by an average of 15%. For the subjects who consumed the apple sauce pre-meal, their calorie intake decreased by 6%. Those who drank the apple juice with added fibre saw a decrease in calorie intake by 1%, but those who just drank the plain apple juice actually saw an increase total calorie intake by 3%.
So is it all bad news for the smoothie? Not quite.
Firstly if you are having a smoothie, make sure you make your own so that you know exactly what and how much is in it. Focus on water rich fruits and vegetables – carrots, beetroot and cucumber make good additions. To up the satiety levels try adding protein – a nut butter, almond milk, or protein powder – and to prevent the sugar spike and dip add a slow release, low GI carb such as oats.
Smoothies are a great way to get a vitamin hit on the go and, with the right ingredients, a great post-workout refuelling snack, but it is important to regard them as a meal or substantial snack in and of themselves, rather than as an accompaniment to something more.
I’m not ready to give up my smoothie habit yet, but I’ll definitely be thinking more about what goes into them in future!