Have you ever opted for a freshly squeezed juice instead of a soda because you thought that it was a healthier option? Or perhaps you enjoy creamy and refreshing smoothies during the summer. While both juices and smoothies are made from fresh ingredients and vitamin-loaded fruits and vegetables, are they truly healthy? I hope that in this article, you find out.
Let’s start by distinguishing juices from smoothies. A smoothie has a denser texture and an opaquer color because it contains dietary fiber, whereas juices are more watery and clear because the fiber is filtered out and removed. Both are made from fruits and/or vegetables. Additional ingredients like protein powder or yoghurt can be added to smoothies, which along with the fiber, can contribute to its thicker texture.
Health organizations like the NHS and WHO recommend eating 5 portions of fruits and vegetables a day, which amounts to about 400 grams in total [5, 7]! I don’t know about you, but I really struggle meeting that goal so here’s where a smoothie may be helpful, as they often incorporate a fruit and/or vegetable serving. But have you ever considered how blending affects the nutritional properties of fruits and vegetables?
Effect of blending on plant cells
The cells in fruits and vegetables are surrounded by a strong material that cannot be broken down by our body’s enzymes. This material is dietary fiber, which in this case can include cellulose and pectin. Since we cannot digest dietary fiber, it ends up in our large intestine where our gut microbes can ferment it. This means that the nutrients inside intact cells cannot be absorbed in our small intestine because our enzymes are unable to reach them and break them down first.
We should keep in mind that vitamins are not the only components present inside of cells. By blending, we also make sugars in fruit more available for absorption in our body, which is an undesirable effect because it can result in a spike in our blood sugar levels. People who have consistently high blood sugar levels also have a higher risk of developing diabetes. Therefore, it is important to be mindful of our food and drink choices.
Effect of blending on sugar absorption
The effect that food has on our blood sugar levels is known as a glycemic response. Juices tend to cause a higher glycemic response because sugars are more available for absorption, a faster gastric (stomach) emptying and the absence of fiber.
In general, solid foods take longer to be digested by our stomach, which means that they are released into our small intestine more slowly than liquid foods. The speed in which food is released from our stomach is called gastric emptying, and it influences our feeling of satiety as well as our body’s glycemic response to a food [3]. This is why in general, liquid foods that are high in sugar increase our blood sugar levels faster than solid foods do. Soluble fiber can slow down gastric emptying by increasing the viscosity of our chewed food [1], which is why we would expect smoothies to have a lower glycemic response than juices.
Do all juices and smoothies have a high glycemic index?
It depends on which ingredients you use. Fruits like apples and prunes tend to have a low glycemic index while fruits like watermelon and ripe bananas tend to have a higher glycemic index [6]. Further, the lack of fiber and protein in fruit juices, and the fact that they can be consumed much faster than a whole fruit often results in a higher glycemic response [4].
However, blending does not always seem to cause a higher glycemic response. A study found that blending apples and blackberries resulted in a lower glycemic response as compared to eating the whole fruits [3]. It was suggested that this effect could be because the seeds of the fruit were also blended in the making of the smoothies. Seeds have additional fiber, fat, and protein, which could have slowed down the rate of gastric emptying, thereby leading to a lower glycemic response [1, 3]. This effect could have been observed because we do not normally eat the seeds in fruits, and even if we did, we cannot always get all the nutrients from them because we cannot breakdown the cell walls.
How can we lower or body’s glycemic response to juices and smoothies?
While more studies are needed to better understand the role of blending on glycemic response, it seems that by adding other ingredients to our smoothies or by eating our juice along a meal, we could influence our body’s glycemic response.
It has been suggested that by adding some protein and/or fat, we could lower our body’s glycemic response by slowing down the rate of gastric emptying [1, 2, 3, 4]. Putting this into practice could mean consuming your juice along a healthy meal so that you don’t drink it on an empty stomach. It could also mean adding protein and/or fat sources to your smoothie, such as yoghurt, protein powders, chia seeds, or nut butters.
Another way in which you can prevent your blood sugar levels from spiking is by doing some movement after eating. This could be as simple as going for a short walk or even doing some cleaning. The idea behind this is that as you move, your muscles will use energy, so the sugar molecules in your blood will be taken to your muscles, which prevents you from getting a blood sugar spike [2].
So, should I choose a juice or a smoothie?
There is no answer fits all. People struggling to eat the recommended daily servings of fruits and vegetables would perhaps benefit from smoothies because they still contain dietary fiber. For people trying to get a sugar boost as a way to get quick energy, a juice may be a better option. For people wanting to lower their blood sugar levels but craving a juice, perhaps a good option would be to consume a smoothie instead, made with fruits and vegetables that have a low glycemic index. Also important to mention is that moderation is very important, but this does not only apply to food in my opinion. It is important to try to have a balanced life, whatever that looks like for you. So, if having fruit juice once in a while is something that makes you happy, then you should fully enjoy it!
In general, the effect that a food will have person A may be different from the effect it will have on person B, so the aim of my article is not to give you dietary advice because (1) I am not qualified for that and (2) I don’t know your personal situation. My goal is to provide you with more information so that you can make the choice that suits you best. With that said, here are the main takeaways from the article:
✅ Smoothies contain fiber whereas juices do not. This is one of the reasons why juices cause a higher glycemic response.
✅ Some fruits have a higher glycemic index than others.
✅ Blending makes nutrients more accessible to our enzymes.
✅ You can reduce a food’s glycemic response by doing some movement (like walking) after eating or by adding a source of fat and/or protein to your food.
I hope you learnt something new! Let me know in the comments if you have anything else to add, let’s share our knowledge 🌱.
Sources
If you are interested on learning more about this topic, here are the sources I used in the writing of this post:
[1] Crummett, L. T., & Grosso, R. J. (2022). Postprandial Glycemic Response to Whole Fruit versus Blended Fruit in Healthy, Young Adults. Nutrients, 14, 4565. https://doi.org/10.3390/nu14214565
[2] Glucose Revolution. (2024, February 21). 10 Life-Changing Glucose Hacks: easy tricks that will change how you feel forever | Episode 3 of 18 [Video]. YouTube. https://www.youtube.com/watch?v=1PkshTBkWZ8
[3] Gonzalez, J. T. (2024). Are all sugars equal? Role of the food source in physiological responses to sugars with an emphasis on fruit and fruit juice. European Journal of Nutrition. https://doi.org/10.1007/s00394-024-03365-3
[4] Hill, A. (2019, April 8). Is juicing safe and healthy if you have diabetes? Healthline. https://www.healthline.com/nutrition/juicing-for-diabetics#recommendation
[5] NHS UK. (2023, February 10). 5 A Day portion sizes. NHS UK. https://www.nhs.uk/live-well/eat-well/5-a-day/portion-sizes/
[6] The Healthline Editorial Team. (2020, December 14). Diabetes Nutrition Guide: Understanding the Glycemic Index. Healthline. https://www.healthline.com/health/type-2-diabetes/fruits-vegetables#fruits-and-vegetables
[7] World Health Organization: WHO. (2020, April 29). Healthy diet. WHO. https://www.who.int/news-room/fact-sheets/detail/healthy-diet#:~:text=At%20least%20400%20g%20(i.e.,cassava%20and%20other%20starchy%20roots.
All the best,
~ Lucia