Note: This article was originally posted on August 13, 2023, and was updated and reposted on November 25, 2025
Introduction
In the interest of time, many people throw a cup or more of fruit, some green veggies, and maybe some protein powder into a blender to make a smoothie for breakfast. But most people don’t realize how blending affects their blood sugar, gut microbiome, and how much food they eat.
Making a Smoothie
For people with challenges keeping blood sugar stable, or having pre-diabetes or diabetes, a smoothie made with fruit is something to reconsider. Pureed fruit affects blood sugar very differently from eating the same type and amount of fruit, whole and intact.
Cellular versus Acellular Carbohydrate
Cellular carbohydrates come from whole, intact foods where the carbohydrate is still inside the cell wall. These foods take longer to digest and to be absorbed into the bloodstream than ground or pureed foods.
Carbohydrates that have been pureed, like fruit in a smoothie, or ground, like flour made from grain, are now outside their cell wall (acellular carbohydrate). As a result, pureed and ground foods are digested more quickly because the fiber that normally slows absorption is disrupted.
A Smoothie as “Pre-Chewed” Food
Most people think digestion begins in the stomach, but it starts in the mouth, when we chew food. As unappealing as it sounds, smoothies are “pre-chewed” food.
Drinking carbohydrates, rather than eating them, can result in spikes in blood sugar, affect gut bacteria, and can even impact how much food we eat due to hunger that follows a quick rise and then fall in blood sugar from the insulin response to quickly digested carbs.
Research shows that when fruit is pureed or juiced, blood glucose rises more rapidly and remains higher than when the same fruit is eaten whole [1]. This occurs because the blender has already broken down the cell walls, doing some of the work that chewing would normally do. For people with higher than ideal blood sugar, or pre-diabetes or diabetes, drinking a morning smoothie instead of eating the same foods intact can lead to a significantly different blood sugar response.
It is important to note that 60 g of whole fruit, 60 g of pureed fruit, and 60 g of juiced fruit all contain the same amount of carbohydrate and have similar Glycemic Index (GI) values. But the GI only tells us how quickly a food raises blood sugar, not how high blood sugar will go. Recent research also emphasizes that food structure, not just carbohydrate content, plays a critical role in blood glucose control [2].
Whole berries or fruit (cellular carbohydrate) are preserved within their cell walls until the digestive juices in the stomach begin to break them down. Once released, the carbohydrate is then absorbed mainly in the large intestine (colon).
Acellular carbohydrates, such as the fruit in smoothies, begin digestion in the small intestine rather than the colon. Early digestion of acellular carbohydrates can alter gut microbial fermentation and is thought to contribute to an imbalance in gut microbes (gut dysbiosis) or leaky gut (increased intestinal permeability) [3].
Drinking carbohydrate-containing foods, rather than eating them, may promote overconsumption and contribute to leptin resistance. Leptin is the hormone that signals us when we are hungry via a negative feedback loop. This feedback loop is thought to become dysregulated when we consume large amounts of acellular carbohydrates, such as pureed fruit. Leptin resistance occurs when the body fails to respond properly to leptin. Some research suggests that acellular carbohydrates alter leptin signaling, increase inflammation, and disturb the gut microbiota, which over time can blunt the body’s feedback loop that signals the brain that we are full [4].
Final Thoughts
Digestion begins in the mouth when we chew food, and there is a big difference between how whole, intact carbohydrates are absorbed and how blended smoothies are absorbed.
Smoothies are “pre-chewed food” that can disrupt blood sugar, alter our gut microbiome, and increase the total amount of food we consume.
Instead of throwing fruit, veggies, and protein powder into a blender, reach for half a cup of berries to put over top a cup of cottage cheese or plain Greek yogourt with a few spoons of hemp hearts, and grab a handful of snap peas or baby carrots. This quick, light meal that has the protein and leucine adults need to preserve their muscle mass — and there is no blender to clean afterwards!
More Info
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References
[1] Haber GB, Heaton KW, Murphy D, Legg NJ. 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. [https://pubmed.ncbi.nlm.nih.gov/71495/]
[2] Forde CG, Frank T, Leong C. Interrelations Between Food Form, Texture, and Matrix. Nutrients. 2022;14(4):731. doi:10.3390/nu14040731 [https://pmc.ncbi.nlm.nih.gov/articles/PMC9174310/]
[3] Stull AJ, Apolzan JW, Thalacker-Mercer AE, Iglay HB, Campbell WW. Liquid and solid meal replacement products differentially affect postprandial appetite and food intake in older adults. J Am Diet Assoc. 2008 Jul;108(7):1226-30. doi: 10.1016/j.jada.2008.04.014. PMID: 18589034; PMCID: PMC2556245. [https://pubmed.ncbi.nlm.nih.gov/18589034/]
[4] Spreadbury I. Comparison with ancestral diets suggests dense acellular carbohydrates promote an inflammatory microbiota, and may be the primary dietary cause of leptin resistance and obesity. Diabetes Metab Syndr Obes. 2012;5:175-89. doi: 10.2147/DMSO.S33473. Epub 2012 Jul 6. PMID: 22826636; PMCID: PMC3402009. [https://pubmed.ncbi.nlm.nih.gov/22826636/]
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