Eating intact grains, beans, and nuts (as opposed to bread, hummus, and nut butters) may have certain advantages for our gut flora and blood sugar control, raising questions about blending fruits and vegetables.
Are Green Smoothies Bad for You?
Fruits and vegetables are the most nutrient-dense foods on the planet, and dark green leafy vegetables lead the pack. Each of the top five so-called “powerhouse fruits and vegetables” were greens. And so, if we blend them up in a smoothie (or soup or sauce), we’re taking the food with the most nutrition and breaking all the cell walls to dump that nutrition into our bloodstream. Chewing is good, but blending is better, in terms of digestive efficiency and absorbing nutrients.
But if we suck up all that nutrition such that none of it makes it down to our colon, might we be starving our microbial selves? The reason intact grains, beans, and nuts are better than bread, hummus, and nut butters is that no matter how well we chew, intact food particles make it down to your colon where they can offer a smorgasbord for your good bacteria. But if your grains, beans, and nuts are finely ground up into flour or paste before you eat it, you may be leaving your gut flora high and dry. Would the same be true for fruits and vegetables?
There are special classes of phytonutrients in fruits and vegetables that appear to protect against colon cancer. They can escape digestion and absorption in our stomach and small intestine, and end up in our colon to act as prebiotics. No matter how much we chew, they stay attached to the fiber. But if we use a blender, might we prematurely detach these nutrients? No. Even if you blend in a high-speed blender for five minutes, they remain bound to the fiber for transport down to your colon bacteria. You can do smoothie experiments on people with ileostomy bags that drain the contents of the small intestine, and show that most of the polyphenol phytonutrients make it out intact. So we don’t have to worry we may be robbing Peter to pay Paul when we blend fruits and vegetables. Is there any downside to smoothies, then?
Well, just as smaller particle size may improve digestive efficiency and gastrointestinal absorption of nutrients from fruits and vegetables, the same may be true for grains. But the concern is that this could boost starch availability and cause a blood sugar spike. For example, here’s the rise and fall in our blood sugar in the four hours after eating a half cup of brown rice, eliciting a nice gentle bump in our insulin levels to take care of it. Doesn’t even go above normal fasting blood sugar levels. But what if we ate the same amount of brown rice, but first ground into brown rice flour, so like a cream of brown rice hot cereal? You get twice the blood sugar, twice the insulin spike. Same amount of food, just in a different form. Another reason why intact whole grains are better than whole grain flour products.
Even just chewing really well can boost the glycemic and insulin response. Here’s if you just chew rice regularly and here’s if you chew really well. The smaller rice particles empty out of your stomach faster, producing greater blood sugar and insulin responses. It’s ironic that there were health crusaders pushing people to chew more to digest their food better, but if what you’re chewing is a five-cheese pizza, maybe it’s better not to digest so well. Some have even suggested that diabetics and obese persons not chew their food so much. Swallowing diced food without chewing would not only reduce the pleasure of eating, though, but people could choke on it. Still, though, they suggest it could be a simple way to allow patients to reduce their blood sugar levels without fundamentally altering their diets and may thus prove more acceptable than having to do the unthinkable—eat high fiber foods like beans, which have been shown to blunt blood sugar spikes.
Even blended beans, like hummus? Yes, unlike grains, blending legumes does not affect their glycemic response. So, circling back to the smoothie question, is fruit more like grains or more like beans? If you liquefy fruit in a blender to make a smoothie, do you risk spiking your blood sugar too high? We’ll find out next.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.
Please consider volunteering to help out on the site.
- S Hagl, H Deusser, B Soyalan, C Janzowski, F Wil, H Dietrich. F W Albert, S Rohner, E Richling. Colonic availability of polyphenols and D-(-)-quinic acid after apple smoothie consumption. Mol Nutr Food Res. 2011 Mar;55(3):368-77.
- N W Read, I M Welch, C J Austen, C Barnish, C E Bartlett, A J Baxter, G Brown, M E Compton, K E Hume, I Storie, et al. Swallowing food without chewing; a simple way to reduce postprandial glycaemia. Br J Nutr. 1986 Jan;55(1):43-7.
- R W Simpson, J McDonald, M L Wahlqvis, L Atley, K Outch K. Food physical factors have different metabolic effects in nondiabetics and diabetics. Am J Clin Nutr. 1985 Sep;42(3):462-9.
- V Ranawana, M E Clegg, A Shafat, C J Henry. Postmastication digestion factors influence glycemic variability in humans. Nutr Res. 2011 Jun;31(6):452-9.
- Y Zhu, W H Hsu, J H Hollis. Increasing the number of masticatory cycles is associated with reduced appetite and altered postprandial plasma concentrations of gut hormones, insulin and glucose. Br J Nutr. 2013 Jul 28;110(2):384-90.
- A Padayachee, G Netzel, M Netzel, L Day, D Mikkelsen, M J Gidley. Lack of release of bound anthocyanins and phenolic acids from carrot plant cell walls and model composites during simulated gastric and small intestinal digestion. Food Funct. 2013 Jun;4(6):906-16.
- H J Smit, E K Kemsley, H S Tapp, C J Henry. Does prolonged chewing reduce food intake? Fletcherism revisited. Appetite. 2011 Aug;57(1):295-8.
- T Turley. The Merchant of Venice: Horace Fletcher and "Fletcherism". Nutrition Today: November/December 1986.
- L R Brewer, J Kubola, S Siriamornpun, T J Herald, Y C Shi. Wheat bran particle size influence on phytochemical extractability and antioxidant properties. Food Chem. 2014;152:483-90.
- J Pérez-Jiménez, M E Díaz-Rubio, F Saura-Calixto. Non-extractable polyphenols, a major dietary antioxidant: occurrence, metabolic fate and health effects. Nutr Res Rev. 2013 Dec;26(2):118-29.
- K O'Dea, P J Nestel, L Antonoff. Physical factors influencing postprandial glucose and insulin responses to starch. Am J Clin Nutr. 1980 Apr;33(4):760-5.
- K H van het Hof, L B Tijburg, K Pietrzik, J A Weststrate. Influence of feeding different vegetables on plasma levels of carotenoids, folate and vitamin C. Effect of disruption of the vegetable matrix. Br J Nutr. 1999 Sep;82.
- O W Wooley, S C Wooley, R B Dunham. Can calories be perceived and do they affect hunger in obese and nonobese humans? J Comp Physiol Psychol. 1972 Aug;80(2):250-8.
- J Di Noia. Defining powerhouse fruits and vegetables: a nutrient density approach. Prev Chronic Dis. 2014 Jun 5;11:E95.
- E Kennedy, P Racsa, G Dallal, A H Lichtenstein, J Goldberg, P Jacques, R Hyatt. Alternative approaches to the calculation of nutrient density. Nutr Rev. 2008 Dec;66(12):703-9.
- E D Sonnenburg, J L Sonnenburg. Starving our microbial self: the deleterious consequences of a diet deficient in microbiota-accessible carbohydrates. Cell Metab. 2014 Nov 4;20(5):779-86.
- K M Tuohy, L Conterno, M Gasperott, R Viola. Up-regulating the human intestinal microbiome using whole plant foods, polyphenols, and/or fiber. See comment in PubMed Commons belowJ Agric Food Chem. 2012 Sep 12;60(36):8776-82.
- A L Hovey, G P Jones, H M Devereux, K Z Walker. Whole cereal and legume seeds increase faecal short chain fatty acids compared to ground seeds. Asia Pac J Clin Nutr. 2003;12(4):477-82.
- Rossi M, Bosetti C, Negri E, Lagiou P, La vecchia C. Flavonoids, proanthocyanidins, and cancer risk: a network of case-control studies from Italy. Nutr Cancer. 2010;62(7):871-7.
Images thanks to Joanna Slodownik via Flickr.
Fruits and vegetables are the most nutrient-dense foods on the planet, and dark green leafy vegetables lead the pack. Each of the top five so-called “powerhouse fruits and vegetables” were greens. And so, if we blend them up in a smoothie (or soup or sauce), we’re taking the food with the most nutrition and breaking all the cell walls to dump that nutrition into our bloodstream. Chewing is good, but blending is better, in terms of digestive efficiency and absorbing nutrients.
But if we suck up all that nutrition such that none of it makes it down to our colon, might we be starving our microbial selves? The reason intact grains, beans, and nuts are better than bread, hummus, and nut butters is that no matter how well we chew, intact food particles make it down to your colon where they can offer a smorgasbord for your good bacteria. But if your grains, beans, and nuts are finely ground up into flour or paste before you eat it, you may be leaving your gut flora high and dry. Would the same be true for fruits and vegetables?
There are special classes of phytonutrients in fruits and vegetables that appear to protect against colon cancer. They can escape digestion and absorption in our stomach and small intestine, and end up in our colon to act as prebiotics. No matter how much we chew, they stay attached to the fiber. But if we use a blender, might we prematurely detach these nutrients? No. Even if you blend in a high-speed blender for five minutes, they remain bound to the fiber for transport down to your colon bacteria. You can do smoothie experiments on people with ileostomy bags that drain the contents of the small intestine, and show that most of the polyphenol phytonutrients make it out intact. So we don’t have to worry we may be robbing Peter to pay Paul when we blend fruits and vegetables. Is there any downside to smoothies, then?
Well, just as smaller particle size may improve digestive efficiency and gastrointestinal absorption of nutrients from fruits and vegetables, the same may be true for grains. But the concern is that this could boost starch availability and cause a blood sugar spike. For example, here’s the rise and fall in our blood sugar in the four hours after eating a half cup of brown rice, eliciting a nice gentle bump in our insulin levels to take care of it. Doesn’t even go above normal fasting blood sugar levels. But what if we ate the same amount of brown rice, but first ground into brown rice flour, so like a cream of brown rice hot cereal? You get twice the blood sugar, twice the insulin spike. Same amount of food, just in a different form. Another reason why intact whole grains are better than whole grain flour products.
Even just chewing really well can boost the glycemic and insulin response. Here’s if you just chew rice regularly and here’s if you chew really well. The smaller rice particles empty out of your stomach faster, producing greater blood sugar and insulin responses. It’s ironic that there were health crusaders pushing people to chew more to digest their food better, but if what you’re chewing is a five-cheese pizza, maybe it’s better not to digest so well. Some have even suggested that diabetics and obese persons not chew their food so much. Swallowing diced food without chewing would not only reduce the pleasure of eating, though, but people could choke on it. Still, though, they suggest it could be a simple way to allow patients to reduce their blood sugar levels without fundamentally altering their diets and may thus prove more acceptable than having to do the unthinkable—eat high fiber foods like beans, which have been shown to blunt blood sugar spikes.
Even blended beans, like hummus? Yes, unlike grains, blending legumes does not affect their glycemic response. So, circling back to the smoothie question, is fruit more like grains or more like beans? If you liquefy fruit in a blender to make a smoothie, do you risk spiking your blood sugar too high? We’ll find out next.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.
Please consider volunteering to help out on the site.
- S Hagl, H Deusser, B Soyalan, C Janzowski, F Wil, H Dietrich. F W Albert, S Rohner, E Richling. Colonic availability of polyphenols and D-(-)-quinic acid after apple smoothie consumption. Mol Nutr Food Res. 2011 Mar;55(3):368-77.
- N W Read, I M Welch, C J Austen, C Barnish, C E Bartlett, A J Baxter, G Brown, M E Compton, K E Hume, I Storie, et al. Swallowing food without chewing; a simple way to reduce postprandial glycaemia. Br J Nutr. 1986 Jan;55(1):43-7.
- R W Simpson, J McDonald, M L Wahlqvis, L Atley, K Outch K. Food physical factors have different metabolic effects in nondiabetics and diabetics. Am J Clin Nutr. 1985 Sep;42(3):462-9.
- V Ranawana, M E Clegg, A Shafat, C J Henry. Postmastication digestion factors influence glycemic variability in humans. Nutr Res. 2011 Jun;31(6):452-9.
- Y Zhu, W H Hsu, J H Hollis. Increasing the number of masticatory cycles is associated with reduced appetite and altered postprandial plasma concentrations of gut hormones, insulin and glucose. Br J Nutr. 2013 Jul 28;110(2):384-90.
- A Padayachee, G Netzel, M Netzel, L Day, D Mikkelsen, M J Gidley. Lack of release of bound anthocyanins and phenolic acids from carrot plant cell walls and model composites during simulated gastric and small intestinal digestion. Food Funct. 2013 Jun;4(6):906-16.
- H J Smit, E K Kemsley, H S Tapp, C J Henry. Does prolonged chewing reduce food intake? Fletcherism revisited. Appetite. 2011 Aug;57(1):295-8.
- T Turley. The Merchant of Venice: Horace Fletcher and "Fletcherism". Nutrition Today: November/December 1986.
- L R Brewer, J Kubola, S Siriamornpun, T J Herald, Y C Shi. Wheat bran particle size influence on phytochemical extractability and antioxidant properties. Food Chem. 2014;152:483-90.
- J Pérez-Jiménez, M E Díaz-Rubio, F Saura-Calixto. Non-extractable polyphenols, a major dietary antioxidant: occurrence, metabolic fate and health effects. Nutr Res Rev. 2013 Dec;26(2):118-29.
- K O'Dea, P J Nestel, L Antonoff. Physical factors influencing postprandial glucose and insulin responses to starch. Am J Clin Nutr. 1980 Apr;33(4):760-5.
- K H van het Hof, L B Tijburg, K Pietrzik, J A Weststrate. Influence of feeding different vegetables on plasma levels of carotenoids, folate and vitamin C. Effect of disruption of the vegetable matrix. Br J Nutr. 1999 Sep;82.
- O W Wooley, S C Wooley, R B Dunham. Can calories be perceived and do they affect hunger in obese and nonobese humans? J Comp Physiol Psychol. 1972 Aug;80(2):250-8.
- J Di Noia. Defining powerhouse fruits and vegetables: a nutrient density approach. Prev Chronic Dis. 2014 Jun 5;11:E95.
- E Kennedy, P Racsa, G Dallal, A H Lichtenstein, J Goldberg, P Jacques, R Hyatt. Alternative approaches to the calculation of nutrient density. Nutr Rev. 2008 Dec;66(12):703-9.
- E D Sonnenburg, J L Sonnenburg. Starving our microbial self: the deleterious consequences of a diet deficient in microbiota-accessible carbohydrates. Cell Metab. 2014 Nov 4;20(5):779-86.
- K M Tuohy, L Conterno, M Gasperott, R Viola. Up-regulating the human intestinal microbiome using whole plant foods, polyphenols, and/or fiber. See comment in PubMed Commons belowJ Agric Food Chem. 2012 Sep 12;60(36):8776-82.
- A L Hovey, G P Jones, H M Devereux, K Z Walker. Whole cereal and legume seeds increase faecal short chain fatty acids compared to ground seeds. Asia Pac J Clin Nutr. 2003;12(4):477-82.
- Rossi M, Bosetti C, Negri E, Lagiou P, La vecchia C. Flavonoids, proanthocyanidins, and cancer risk: a network of case-control studies from Italy. Nutr Cancer. 2010;62(7):871-7.
Images thanks to Joanna Slodownik via Flickr.
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Are Green Smoothies Bad for You?
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Content URLDoctor's Note
This is part two of my five-part video series. If you’re just joining the fun, make sure you go back and check out the first installment: Are Green Smoothies Good for You?
Coming up to settle the issue once and for all (until new science comes out, that is), the upcoming final three are:
- Green Smoothies: What Does the Science Say?
- Liquid Calories: Do Smoothies Lead to Weight Gain?
- The Downside of Green Smoothies
Frankly the more beans, the better, however you get them:
- Beans and the Second Meal Effect
- Canned Beans or Cooked Beans?
- Increased Lifespan from Beans
- Beans, Beans, They’re Good For Your Heart
- Cooked Beans or Sprouted Beans?
What about the phytates though? They’re good for you!
- Phytates for the Prevention of Cancer
- Phytates for Rehabilitating Cancer Cells
- Phytates for the Treatment of Cancer
Check out this video about The Downside to Banana Smoothies for Polyphenol Absorption and what about Banana vs. Mango Smoothies for Polyphenol Absorption? Check out the video.
If you’re interested, check out my Bananas in Smoothies live presentation with Q&A
If you haven’t yet, you can subscribe to my videos for free by clicking here. Read our important information about translations here.