Concerns about smoothies and oxalic acid, nitrate availability, dental erosion, and weight gain are addressed.
The Downside of Green Smoothies
4.5/5 - (184 votes)
If you split women into two groups and tell them to eat as much soup as they want, but half are given big spoons and told to eat fast, and the other group is given small spoons and told to eat slow, the slow group ended up feeling more satiated, despite eating less food. The thought is that prolonged meal duration can allow more time for our own body’s I’ve-had-enough signals to develop before too many calories have been consumed. After all, we evolved for millions of years before cooking, when undomesticated fruits and vegetables were much tougher and more fibrous. Our body is built to expect us to take our time to eat.
There weren’t any blenders on the African savannah either. In smoothie form, you can drink fruits and vegetables at about two cups a minute—ten times faster than what it might take to eat them in solid form. Liquid calories can be consumed so quickly they can undermine our body’s capacity to regulate food intake at healthy levels. It’s not the liquid texture per se, but the high rate of consumption at which liquids are normally consumed. And so, blend all the smoothies you want, but better to sip them slowly, over a half hour or so, rather than gulping them down.
Even slowly sipped, though, an all-fruit smoothie may not be as filling as whole fruit; so, the more greens you can add to your smoothie the better, and you can add ground flax seeds. The thicker the smoothie, the less hungry you may be one, two—even four hours later, and flax seeds make for thick milkshakey-type smoothies. One tablespoon of flaxseeds was found to significantly suppress appetite and calorie intake. Less hunger, more satiety, more filling, less prospective food intake—meaning you give someone a meal two hours after the tablespoon of flax, and they eat significantly less. All the while, possibly leading to significant reduction in cholesterol. This is just one week after about a tablespoon a day.
The fat naturally found in flaxseeds can also help maximize the absorption of fat-soluble phytonutrients. There’s a threshold for optimal absorption that can be reached with just like three walnuts’ worth of fat. So, if you’re trying to reduce added fats, a green smoothie with some nuts, seeds, or avocado can enable you to take full advantage of the healthiest foods on the planet: dark green leafy vegetables.
Smoothies also allow us to eat parts of fruits and vegetables we might not otherwise. If instead of lemon juice, here in the Mayo Clinic’s basic green smoothie recipe, you used a little wedge of lemon, you might get some seeds and peel, which, in vitro at least, appear to suppress both breast cancer and colon cancer cell growth.
Clinical studies on smoothies show what you’d expect to see from eating great foods like greens and berries—enhanced athletic performance and recovery, boosting the antioxidant power of your bloodstream, potentially improving arterial function in the short-term, and the long-term. Kiwifruit smoothies protect against DNA damage and strawberry smoothies against inflammation. Of course so would, presumably, just eating greens, kiwis, and berries intact. There has been concern expressed that drinking green smoothies would bypass the nitrate-reducing bacteria in the mouth, but our body’s way too smart for that, and pumps nitrate back into our salivary glands. So, even if you deposited greens directly in your stomach with a tube, you’d still produce the nitric oxide so important for artery health.
Concerns have been raised about the oxalic acid in vegetables might increase kidney stone risk, but as I’ve explained in the past, if anything the opposite might be the case. So, are there any downsides of smoothie consumption?
Whether lemon juice or wedge, smoothies can be sour, and any time you’re eating or drinking something sour, you have to careful about eroding the enamel on your teeth. If you soak teeth in a smoothie for an hour, significant enamel is eroded away. But who soaks their teeth in a smoothie for an hour? What if you instead study the effects of smoothies in situ, meaning in position, as opposed to in vitro, meaning in glass? If you make people wear slabs of enamel in their mouths while they drink a smoothie to replicate a typical tooth exposure, they do find almost as much erosion as drinking Diet Coke, so it’s recommended that smoothies be consumed through a straw, similar to the advice given for other acidic beverages like soda or hibiscus tea. Compared to control, drinking juice through a straw has less of an acidic effect than swishing it around in your mouth, so avoid swishing smoothies around in your mouth, and you want to wait at least an hour before brushing so as not to brush your enamel in a softened state. But rinsing your mouth out with water after drinking is a good idea, as it can help rinse away some of the acids to protect your teeth.
And one final caveat for smoothies: when I advocate green smoothies to boost fruit and vegetable consumption I’m talking about whole food smoothies, not made from juice, or added sugars, or human organs. Some women choose to consume their afterbirth. Though described as “replenishing and delicious,” the problem with eating your placenta is that one of the functions of the placenta is to filter out toxins, and so, it may be contaminated with heavy metals, as well as pose a food poisoning risk if consumed raw, like in a smoothie. Green smoothies are great, but I’d be cautious about drinking certain types of red smoothies.
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.
- G B Haber, K W Heaton, D Murphy, L F Burroughs. Depletion and disruption of dietary fibre. Effects on satiety, plasma-glucose, and serum-insulin. Lancet. 1977 Oct 1;2(8040):679-82.
- C de Graaf. Why liquid energy results in overconsumption. Proc Nutr Soc. 2011 May;70(2):162-70.
- Y McLeay, M J Barnes, T Mundel, S M Hurst, R D Hurst, S R Stannard. Effect of New Zealand blueberry consumption on recovery from eccentric exercise-induced muscle damage. J Int Soc Sports Nutr. 2012 Jul 11;9(1):19.
- T W George, S Waroonphan, C Niwat, M H Gordon, J A Lovegrove. Effects of acute consumption of a fruit and vegetable purée-based drink on vasodilation and oxidative status. Br J Nutr. 2013 Apr 28;109(8):1442-52.
- T George, C Niwat, S Waroonphan, M H Gordon, J A Lovegrove. Effects of chronic and acute consumption of fruit- and vegetable-puree-based drinks on vasodilation, risk factors for CVD and the response as a result of the eNOS G298T polymorphism. Proc Nutr Soc. 2009 May;68(2):148-61.
- T W George, E Paterson, S Waroonphan, M H Gordon, J A Lovegrove. Effects of chronic consumption of fruit and vegetable puree-based drinks on vasodilation, plasma oxidative stability and antioxidant status. J Hum Nutr Diet. 2012 Oct;25(5):477-87.
- J Kim, G K Jayaprakasha, R M Uckoo, B S Patil. Evaluation of chemopreventive and cytotoxic effect of lemon seed extracts on human breast cancer (MCF-7) cells. Food Chem Toxicol. 2012 Feb;50(2):423-30.
- S Ibrugger, M Kristensen, M S Mikkelsen, A Astrup. Flaxseed dietary fiber supplements for suppression of appetite and food intake. Appetite. 2012 Apr;58(2):490-5.
- M Kristensen, M G Jensen, J Aarestrup, K E Petersen, L Sondergaard, M S Mikkelsen, A Astrup. Flaxseed dietary fibers lower cholesterol and increase fecal fat excretion, but magnitude of effect depend on food type. Nutr Metab (Lond). 2012 Feb 3;9:8.
- S M Blacker, S L Creanor, S Creanor. An in vitro investigation of the initial pH and titratable acidity of a selection of fruit smoothies. Dent Update. 2011 Nov;38(9):604-6, 608-9.
- B H Collins, A Horska, P M Hotten, C Riddoch, A R Collins. Kiwifruit protects against oxidative DNA damage in human cells and in vitro. Nutr Cancer. 2001;39(1):148-53.
- I Edirisinghe, K Banaszewski, J Cappozzo, K Sandhya, C L Ellis, R Tadapaneni, C T Kappagoda, B M Burton-Freeman. Strawberry anthocyanin and its association with postprandial inflammation and insulin. Br J Nutr. 2011 Sep;106(6):913-22.
- R D Mattes, D Rothacker. Beverage viscosity is inversely related to postprandial hunger in humans. Physiol Behav. 2001 Nov-Dec;74(4-5):551-7.
- C de Graaf. Texture and satiation: the role of oro-sensory exposure time. Physiol Behav. 2012 Nov 5;107(4):496-501.
- NA. Cataract Surgery, Choose the time. Mayo Clinic Health Letter Volume 32 Number 5 May 2014.
- S R Gotlz, T N Sapper, M L Failla, W W Campbell, M G Ferruzzi. Carotenoid bioavailability from raw vegetables and a moderate amount of oil in human subjects is greatest when the majority of daily vegetables are consumed at one meal. Nutr Res. 2013 May;33(5):358-66.
- J Selander, A Cantor, S M Young, D C Benyshek. Human maternal placentophagy: a survey of self-reported motivations and experiences associated with placenta consumption. Ecol Food Nutr. 2013;52(2):93-115.
- W Lubell-Snyder, T McKinley. Placentophagia: stir-fry, smoothie or raw? Midwifery Today Int Midwife. 2011-2012 Winter;(100):21-3.
- C W Coyle, K E Hulse, K L Wisner, K E Driscoll, C T Clark. Placentophagy: therapeutic miracle or myth? Arch Womens Ment Health. 2015 Jun 4.
- S M Blacker, R G Chadwick. An in vitro investigation of the erosive potential of smoothies. Br Dent J. 2013 Feb;214(4):E9.
- A M Andrade, G W Greene, K J Melanson. Eating slowly led to decreases in energy intake within meals in healthy women. J Am Diet Assoc. 2008 Jul;108(7):1186-91.
- K Gustafsson, N G Asp, B Hagander, M Nyman. Satiety effects of spinach in mixed meals: comparison with other vegetables. Int J Food Sci Nutr. 1995 Nov;46(4):327-34.
- A O Ademosun, G Oboh, S Passamonti, F Tramer, L Ziberna, A A Boligon, M L Athayde. Inhibition of metalloproteinase and proteasome activities in colon cancer cells by citrus peel extracts. J Basic Clin Physiol Pharmacol. 2015 Sep 1;26(5):471-7.
- M D Sorensen, R S His, T Chi, N Shara, J Wactawski-Wende, A J Kahn, H Wang, L Hou, M L Stoller, Women’s Health Initiative Writing Group. Dietary intake of fiber, fruit and vegetables decreases the risk of incident kidney stones in women: a Women's Health Initiative report. J Urol. 2014 Dec;192(6):1694-9.
- H Ali, J F Tahmassebi. The effects of smoothies on enamel erosion: an in situ study. Int J Paediatr Dent. 2014 May;24(3):184-91.
- J F Tahmassebi, P Kandiah, S Sukeri. The effects of fruit smoothies on enamel erosion. Eur Arch Paediatr Dent. 2014 Jun;15(3):175-81.
- Y B Aswini, P S Tangade, A V Ankola, L Nagesh, H Pradnya. The effect of different methods of drinking a carbonated beverage on the pH of dental plaque: an in vivo study. Oral Health Prev Dent. 2005;3(4):237-41.
Images thanks to Morning smoothie and moppet65535 via Flickr.
- antioxidants
- avocados
- berries
- breast cancer
- caloric restriction
- calories
- cancer
- cardiovascular disease
- cholesterol
- Coca-Cola
- colon cancer
- dental health
- DNA damage
- fat
- flaxseeds
- food poisoning
- foodborne illness
- fruit
- fruit juice
- greens
- heart disease
- heavy metals
- hibiscus tea
- inflammation
- kidney disease
- kidney stones
- kiwifruit
- lemons
- nitrates
- nitric oxide
- nuts
- oxidative stress
- phytonutrients
- seeds
- smoothies
- soda
- strawberries
- sugar
- tea
- vegetables
- walnuts
- women's health
If you split women into two groups and tell them to eat as much soup as they want, but half are given big spoons and told to eat fast, and the other group is given small spoons and told to eat slow, the slow group ended up feeling more satiated, despite eating less food. The thought is that prolonged meal duration can allow more time for our own body’s I’ve-had-enough signals to develop before too many calories have been consumed. After all, we evolved for millions of years before cooking, when undomesticated fruits and vegetables were much tougher and more fibrous. Our body is built to expect us to take our time to eat.
There weren’t any blenders on the African savannah either. In smoothie form, you can drink fruits and vegetables at about two cups a minute—ten times faster than what it might take to eat them in solid form. Liquid calories can be consumed so quickly they can undermine our body’s capacity to regulate food intake at healthy levels. It’s not the liquid texture per se, but the high rate of consumption at which liquids are normally consumed. And so, blend all the smoothies you want, but better to sip them slowly, over a half hour or so, rather than gulping them down.
Even slowly sipped, though, an all-fruit smoothie may not be as filling as whole fruit; so, the more greens you can add to your smoothie the better, and you can add ground flax seeds. The thicker the smoothie, the less hungry you may be one, two—even four hours later, and flax seeds make for thick milkshakey-type smoothies. One tablespoon of flaxseeds was found to significantly suppress appetite and calorie intake. Less hunger, more satiety, more filling, less prospective food intake—meaning you give someone a meal two hours after the tablespoon of flax, and they eat significantly less. All the while, possibly leading to significant reduction in cholesterol. This is just one week after about a tablespoon a day.
The fat naturally found in flaxseeds can also help maximize the absorption of fat-soluble phytonutrients. There’s a threshold for optimal absorption that can be reached with just like three walnuts’ worth of fat. So, if you’re trying to reduce added fats, a green smoothie with some nuts, seeds, or avocado can enable you to take full advantage of the healthiest foods on the planet: dark green leafy vegetables.
Smoothies also allow us to eat parts of fruits and vegetables we might not otherwise. If instead of lemon juice, here in the Mayo Clinic’s basic green smoothie recipe, you used a little wedge of lemon, you might get some seeds and peel, which, in vitro at least, appear to suppress both breast cancer and colon cancer cell growth.
Clinical studies on smoothies show what you’d expect to see from eating great foods like greens and berries—enhanced athletic performance and recovery, boosting the antioxidant power of your bloodstream, potentially improving arterial function in the short-term, and the long-term. Kiwifruit smoothies protect against DNA damage and strawberry smoothies against inflammation. Of course so would, presumably, just eating greens, kiwis, and berries intact. There has been concern expressed that drinking green smoothies would bypass the nitrate-reducing bacteria in the mouth, but our body’s way too smart for that, and pumps nitrate back into our salivary glands. So, even if you deposited greens directly in your stomach with a tube, you’d still produce the nitric oxide so important for artery health.
Concerns have been raised about the oxalic acid in vegetables might increase kidney stone risk, but as I’ve explained in the past, if anything the opposite might be the case. So, are there any downsides of smoothie consumption?
Whether lemon juice or wedge, smoothies can be sour, and any time you’re eating or drinking something sour, you have to careful about eroding the enamel on your teeth. If you soak teeth in a smoothie for an hour, significant enamel is eroded away. But who soaks their teeth in a smoothie for an hour? What if you instead study the effects of smoothies in situ, meaning in position, as opposed to in vitro, meaning in glass? If you make people wear slabs of enamel in their mouths while they drink a smoothie to replicate a typical tooth exposure, they do find almost as much erosion as drinking Diet Coke, so it’s recommended that smoothies be consumed through a straw, similar to the advice given for other acidic beverages like soda or hibiscus tea. Compared to control, drinking juice through a straw has less of an acidic effect than swishing it around in your mouth, so avoid swishing smoothies around in your mouth, and you want to wait at least an hour before brushing so as not to brush your enamel in a softened state. But rinsing your mouth out with water after drinking is a good idea, as it can help rinse away some of the acids to protect your teeth.
And one final caveat for smoothies: when I advocate green smoothies to boost fruit and vegetable consumption I’m talking about whole food smoothies, not made from juice, or added sugars, or human organs. Some women choose to consume their afterbirth. Though described as “replenishing and delicious,” the problem with eating your placenta is that one of the functions of the placenta is to filter out toxins, and so, it may be contaminated with heavy metals, as well as pose a food poisoning risk if consumed raw, like in a smoothie. Green smoothies are great, but I’d be cautious about drinking certain types of red smoothies.
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.
- G B Haber, K W Heaton, D Murphy, L F Burroughs. Depletion and disruption of dietary fibre. Effects on satiety, plasma-glucose, and serum-insulin. Lancet. 1977 Oct 1;2(8040):679-82.
- C de Graaf. Why liquid energy results in overconsumption. Proc Nutr Soc. 2011 May;70(2):162-70.
- Y McLeay, M J Barnes, T Mundel, S M Hurst, R D Hurst, S R Stannard. Effect of New Zealand blueberry consumption on recovery from eccentric exercise-induced muscle damage. J Int Soc Sports Nutr. 2012 Jul 11;9(1):19.
- T W George, S Waroonphan, C Niwat, M H Gordon, J A Lovegrove. Effects of acute consumption of a fruit and vegetable purée-based drink on vasodilation and oxidative status. Br J Nutr. 2013 Apr 28;109(8):1442-52.
- T George, C Niwat, S Waroonphan, M H Gordon, J A Lovegrove. Effects of chronic and acute consumption of fruit- and vegetable-puree-based drinks on vasodilation, risk factors for CVD and the response as a result of the eNOS G298T polymorphism. Proc Nutr Soc. 2009 May;68(2):148-61.
- T W George, E Paterson, S Waroonphan, M H Gordon, J A Lovegrove. Effects of chronic consumption of fruit and vegetable puree-based drinks on vasodilation, plasma oxidative stability and antioxidant status. J Hum Nutr Diet. 2012 Oct;25(5):477-87.
- J Kim, G K Jayaprakasha, R M Uckoo, B S Patil. Evaluation of chemopreventive and cytotoxic effect of lemon seed extracts on human breast cancer (MCF-7) cells. Food Chem Toxicol. 2012 Feb;50(2):423-30.
- S Ibrugger, M Kristensen, M S Mikkelsen, A Astrup. Flaxseed dietary fiber supplements for suppression of appetite and food intake. Appetite. 2012 Apr;58(2):490-5.
- M Kristensen, M G Jensen, J Aarestrup, K E Petersen, L Sondergaard, M S Mikkelsen, A Astrup. Flaxseed dietary fibers lower cholesterol and increase fecal fat excretion, but magnitude of effect depend on food type. Nutr Metab (Lond). 2012 Feb 3;9:8.
- S M Blacker, S L Creanor, S Creanor. An in vitro investigation of the initial pH and titratable acidity of a selection of fruit smoothies. Dent Update. 2011 Nov;38(9):604-6, 608-9.
- B H Collins, A Horska, P M Hotten, C Riddoch, A R Collins. Kiwifruit protects against oxidative DNA damage in human cells and in vitro. Nutr Cancer. 2001;39(1):148-53.
- I Edirisinghe, K Banaszewski, J Cappozzo, K Sandhya, C L Ellis, R Tadapaneni, C T Kappagoda, B M Burton-Freeman. Strawberry anthocyanin and its association with postprandial inflammation and insulin. Br J Nutr. 2011 Sep;106(6):913-22.
- R D Mattes, D Rothacker. Beverage viscosity is inversely related to postprandial hunger in humans. Physiol Behav. 2001 Nov-Dec;74(4-5):551-7.
- C de Graaf. Texture and satiation: the role of oro-sensory exposure time. Physiol Behav. 2012 Nov 5;107(4):496-501.
- NA. Cataract Surgery, Choose the time. Mayo Clinic Health Letter Volume 32 Number 5 May 2014.
- S R Gotlz, T N Sapper, M L Failla, W W Campbell, M G Ferruzzi. Carotenoid bioavailability from raw vegetables and a moderate amount of oil in human subjects is greatest when the majority of daily vegetables are consumed at one meal. Nutr Res. 2013 May;33(5):358-66.
- J Selander, A Cantor, S M Young, D C Benyshek. Human maternal placentophagy: a survey of self-reported motivations and experiences associated with placenta consumption. Ecol Food Nutr. 2013;52(2):93-115.
- W Lubell-Snyder, T McKinley. Placentophagia: stir-fry, smoothie or raw? Midwifery Today Int Midwife. 2011-2012 Winter;(100):21-3.
- C W Coyle, K E Hulse, K L Wisner, K E Driscoll, C T Clark. Placentophagy: therapeutic miracle or myth? Arch Womens Ment Health. 2015 Jun 4.
- S M Blacker, R G Chadwick. An in vitro investigation of the erosive potential of smoothies. Br Dent J. 2013 Feb;214(4):E9.
- A M Andrade, G W Greene, K J Melanson. Eating slowly led to decreases in energy intake within meals in healthy women. J Am Diet Assoc. 2008 Jul;108(7):1186-91.
- K Gustafsson, N G Asp, B Hagander, M Nyman. Satiety effects of spinach in mixed meals: comparison with other vegetables. Int J Food Sci Nutr. 1995 Nov;46(4):327-34.
- A O Ademosun, G Oboh, S Passamonti, F Tramer, L Ziberna, A A Boligon, M L Athayde. Inhibition of metalloproteinase and proteasome activities in colon cancer cells by citrus peel extracts. J Basic Clin Physiol Pharmacol. 2015 Sep 1;26(5):471-7.
- M D Sorensen, R S His, T Chi, N Shara, J Wactawski-Wende, A J Kahn, H Wang, L Hou, M L Stoller, Women’s Health Initiative Writing Group. Dietary intake of fiber, fruit and vegetables decreases the risk of incident kidney stones in women: a Women's Health Initiative report. J Urol. 2014 Dec;192(6):1694-9.
- H Ali, J F Tahmassebi. The effects of smoothies on enamel erosion: an in situ study. Int J Paediatr Dent. 2014 May;24(3):184-91.
- J F Tahmassebi, P Kandiah, S Sukeri. The effects of fruit smoothies on enamel erosion. Eur Arch Paediatr Dent. 2014 Jun;15(3):175-81.
- Y B Aswini, P S Tangade, A V Ankola, L Nagesh, H Pradnya. The effect of different methods of drinking a carbonated beverage on the pH of dental plaque: an in vivo study. Oral Health Prev Dent. 2005;3(4):237-41.
Images thanks to Morning smoothie and moppet65535 via Flickr.
- antioxidants
- avocados
- berries
- breast cancer
- caloric restriction
- calories
- cancer
- cardiovascular disease
- cholesterol
- Coca-Cola
- colon cancer
- dental health
- DNA damage
- fat
- flaxseeds
- food poisoning
- foodborne illness
- fruit
- fruit juice
- greens
- heart disease
- heavy metals
- hibiscus tea
- inflammation
- kidney disease
- kidney stones
- kiwifruit
- lemons
- nitrates
- nitric oxide
- nuts
- oxidative stress
- phytonutrients
- seeds
- smoothies
- soda
- strawberries
- sugar
- tea
- vegetables
- walnuts
- women's health
Republishing "The Downside of Green Smoothies"
Terms
You may republish this material online or in print under our Creative Commons licence. You must attribute the article to NutritionFacts.org with a link back to our website in your republication.
If any changes are made to the original text or video, you must indicate, reasonably, what has changed about the article or video.
You may not use our material for commercial purposes.
You may not apply legal terms or technological measures that restrict others from doing anything permitted here.
If you have any questions, please Contact Us
Title
The Downside of Green Smoothies
LicenseCreative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)
Content URLDoctor's Note
That’s it—the whole smoothie enchilada! Phew. For those who are sick of smoothies, you will be happy to know the next video will be non-smoothie-related (though will undoubtedly unleash its own storm of controversy!). For those who missed the rest of Smoothiepalooza, here are the first four videos in the series:
- Are Green Smoothies Good for You?
- Are Green Smoothies Bad for You?
- Green Smoothies: What Does the Science Say?
- Liquid Calories: Do Smoothies Lead to Weight Gain?
Was the concern about dental erosion new to you? See more in:
What’s with that nitrate thing? See Don’t Use Antiseptic Mouthwash. What’s the best mouthwash then? See the video What’s the Best Mouthwash? More on nitrate-containing vegetables coming up!
And more on oxalates and kidney stones in:
- How to Prevent Kidney Stones with Diet
- How to Treat Kidney Stones with Diet
- Oxalates in Spinach and Kidney Stones: Should We Be Concerned?
- Kidney Stones and Spinach, Chard, and Beet Greens: Don’t Eat Too Much
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 our free newsletter. With your subscription, you'll also get notifications for just-released blogs and videos. Check out our information page about our translated resources.
Previous Video
Next Video
