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Do Smoothies Cause Overly Rapid Sugar Absorption?

Drinking sugar water is bad for you, as I explored in If Fructose Is Bad, What About Fruit?. If you have people fast and then drink a glass of water with three tablespoons of sugar in it, which is about the amount in a can of soda, you get a big spike in blood sugar within the first hour. Our body freaks out and releases so much insulin that we actually overshoot. By the second hour, we’re relatively hypoglycemic, dropping our blood sugar below where it was when we started out fasting. In response, our body dumps fat into our bloodstream as if we’re starving because our blood sugars just dropped so low. The same thing happens even after drinking apple juice.

In the three hours after eating four and a half cups of apple slices, your blood sugar just goes up and comes down normally. (You can see all of these spikes and drops in my Green Smoothies: What Does the Science Say? video.) What happens if you take in the same amount of sugar in apple juice form—about two cups? Your body overreacts, releasing too much insulin, and you end up dipping below where you started. The removal of fiber in the production of fruit juice can enhance the insulin response and result in this “rebound hypoglycemia.”

What would happen, though, if you put those four and a half cups of sliced apples in a blender with some water and pureed them into an apple smoothie? Despite still having all the fiber, it still caused that hypoglycemic dip. The rebound fall in blood sugars, which occurred during the second and third hours after drinking juice and puree, “was in striking contrast to the practically steady level after eating apples.” This finding not only indicates how important the presence of fiber is, but also perhaps whether or not the fiber is physically disrupted, like in a blender.

Let’s play devil’s advocate. Eating four and a half cups of apples took 17 minutes, but drinking four and a half cups of apples in smoothie form only took about 6 minutes, and you can down two cups of juice in about 90 seconds. So, maybe these dramatic differences have more to do with how fast the fruit entered our system rather than its physical form. If it’s just the speed, we could simply sip the juice over 17 minutes and it should be the same, right? Researchers put it to the test. They found this had the same results as drinking quickly. So, it wasn’t the speed—it was the lack of fiber. What if you disrupt that fiber with blending but sip it as slowly as the apple eating? The results were a little better, but not as good as just eating the apple. The take-away? Eating apples is better than drinking apple smoothies, but who drinks apple smoothies? What about bananas, mangoes, or berries?

There was a study that compared whole bananas to blended bananas and didn’t see any difference, but they only looked for an hour and it was while participants were exercising. Bananas in general, though, may actually improve blood sugars over time. The same goes for mangoes, as demonstrated with powdered mango, and you can’t get any more fiber-disrupted than that. It may be due to a phytonutrient called mangiferin, which may slow sugar absorption through the intestinal wall.

Berries help control blood sugar so well they can counter the effects of sugar water even when they’re pureed in a blender. By adding blended berries to sugar water, you don’t get the hypoglycemic dip and you don’t get that burst of fat in the blood. Drinking blended berries isn’t just neutral—it improves blood sugar control. Again, this is thought to be due to special phytonutrients that may slow sugar uptake into the bloodstream. Indeed, six weeks of blueberry smoothie consumption may actually improve whole body insulin sensitivity.

So, while apple smoothies may be questionable, a recipe like The Mayo Clinic’s basic green smoothie recipe, which is packed with berries and greens, would be expected to deliver the best of both worlds—maximum nutrient absorption without risking overly rapid sugar absorption.


I have a whole series of videos on green smoothies. In Are Green Smoothies Good for You?, I talk about the enhanced nutrient availability absorption. In Are Green Smoothies Bad for You?, I raise the questions about teary-eyed gut flora and intact grains, beans, and nuts. For even more, see Liquid Calories: Do Smoothies Lead to Weight Gain? and The Downside of Green Smoothies.

Is there any limit to whole fruit? See How Much Fruit Is Too Much?.

What about fructose? Is it bad? Watch my videos Apple Juice May Be Worse Than Sugar Water, How Much Added Sugar Is Too Much?, and Big Sugar Takes on the World Health Organization.

Since digesting food creates free radicals, we need to be sure the food we eat is packed with antioxidants. See Minimum “Recommended Daily Allowance” of Antioxidants, How to Reach the Antioxidant “RDA”, and Antioxidant Rich Foods with Every Meal.

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Discuss

Michael Greger M.D., FACLM

Michael Greger, M.D. FACLM, is a physician, New York Times bestselling author, and internationally recognized professional speaker on a number of important public health issues. Dr. Greger has lectured at the Conference on World Affairs, the National Institutes of Health, and the International Bird Flu Summit, testified before Congress, appeared on The Dr. Oz Show and The Colbert Report, and was invited as an expert witness in defense of Oprah Winfrey at the infamous "meat defamation" trial.


30 responses to “Do Smoothies Cause Overly Rapid Sugar Absorption?

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  1. Very interesting as always. ❤
    Nothing on orange, grapefruit, pomegranate etc. juices? ..or blended?
    Are those ‘bad’ as apple juice/smoothie?
    ☺☺☺




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    1. Grapefruit juice seems to have a life of its’ own. My husband read somewhere that drinking grapefruit juice lowers blood pressure significantly. He follows a WFPB diet when I cook, which is 95% of the time, but if he goes out he eats meat or fish, and when he goes to the grocery store he buys cookies, energy bars and chocolate, which he doles out to himself in small amounts at home. He is 5’11” and weighs 159, with no visible fat. His blood pressure had gotten high enough for his doctor to notice. He started drinking two eight ounce glasses daily and indeed, his blood pressure dropped significantly. He now drinks only one glass a day. He went from about 159/80 to 129/68. His pulse stays in the mid 50s. And no, he isn’t a runner. He works outside many hours a day in the yard pruning and grooming shrubs and trees throughout spring, summer and fall and when he takes a walk, I call it a stroll. It is definitely NOT brisk. He is 80 years old.

      A word of warning: grapefruit juice is contraindicated with many medications, so check anything you’re taking if you plan to try this.




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    2. Emanuela,

      Grapefruit and pomegranate have a lower glycemic index (GI) than apples, while oranges have a slightly higher GI. So, it is reasonable to assume that oranges would have a similar if not more significant hypoglycemic dip as the apples in the above study, and grapefruit and pomegranate would not have as significant a dip.

      If you include 1/2cup of blueberries and some spinach in your smoothie, it should protect you from a hypoglycemic dip caused by your juices/smoothies. Other ways to prevent the hypoglycemic dip are drinking the smoothies slowly, or even blending in some flaxseed and eating them with a spoon. In general, smoothies are preferable to juices because the insoluble fiber that is taken out of juices helps to regulate insulin release.

      Hope this helps!

      Julia




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    1. Sean just leave the applesauce more chunky, i.e. less ‘blended’ and or leave (washed/ scrubbbed) peel on to slow down transit time. I toss in berries or bananas just before eating based on the Dr G’s info in video series until more or better studies are out. Can’t hurt and tastes great.




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  2. Great info. thanks! The study re berries was on lingonberries and black currents. Do you think cherries, pomegranates or strawberries would have the same effect on blood sugar? These are some of my favorite smoothie ingredients.




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    1. @rob Nov 21@11:23am

      On strawberries. Blueberries given as one example based on the studies he read. From today’s post:

      “Berries help control blood sugar so well they can counter the effects of sugar water even when they’re pureed in a blender. By adding blended berries to sugar water, you don’t get the hypoglycemic dip and you don’t get that burst of fat in the blood.”




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    2. Hi rob! These sound like perfect ingredients for a smoothie that is not only good for blood sugar control, but delicious too!




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    1. You should try unsweetened vanilla soymilk as well. My smoothies consist of soy milk, water, frozen berries, frozen kale, flax seed, nuts, cacao powder and a flavored vinegar.

      Kind regards, Rob

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  3. Berries, greens and banana and then I add tumeric and amla powder (really small amount since amla is quite tart- found that out the hard way) and voila! a very healthy smoothie.

    A proud and healthy monthly supporter of Nutritionfacts.org




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    1. Bobb thx for info on amla. I’ve wanted to try the powder or better the whole fresh fruit but have heard/ read little about taste. I don’t have a sweet tooth so maybe I’ll do OK ; )




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  4. My general rule is that smoothie is for vegetables and not for fruits for which I enjoy chewing them. Smoothie or even juicing for vegetables allow me to eat more vegetables with better absorption and less time to spend eating. If I am retired or not working then I probably spend more time to eat and chew.




    9
    1. If you include 1/2cup of blueberries and some spinach in your smoothie, it should protect you from a hypoglycemic dip caused by a medium-glycemic food such as pineapple—- pineapple is about 20 points higher than an apple on the glycemic index, so while there are no studies I know of that look specifically at solid vs liquid pineapple consumption and hypoglycemia, it is reasonable to assume that pineapples would have a similar if not more significant hypoglycemic dip as the apples in the above study). Other ways to prevent the hypoglycemic dip are drinking the smoothies slowly, or even blending in some flaxseed and eating them with a spoon.

      Hope this helps!

      Julia




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  5. Hi all, thanks for the great info. Just wondering when is Dr Mike going to have the PBS special? I saw the pilot, but I thought it was supposed to air on my local PBS station in NY. I want to record it and have my parents watch it.

    Thanks




    2
    1. Hi Lou,

      Thanks for asking! Unfortunately, the special premiered only in Detroit Public TV (and streamed online) on August 8th, 2017. Fortunately, it will be airing in more locations soon, but not all. You might be able to find out if it is airing in NY by finding your local PBS station and searching for “How Not to Die” in the schedule.

      I hope this helps and am sorry we can’t provide better information for all the local stations! I hope you and your family are able to catch it.




      1
  6. What is you opinion on eating cooked oats with apples?
    I daily eat a bowl of cooked (with water) whole oats (6 tbsp) with 3 sliced medium apples together with 1 tbsp of raisins, 2 tsp of cinnamon, 1 tsp tumeric, 1tsp of coconut oil and 1 tsp of honey…

    Thank you!




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  7. Since we are sharing smoothie recipes, my daily smoothie: 3-4 oz. of a green plant juice mix (blend of fruit purees/juices, spinach, chlorella, spirulina) from TJ’s, or unsweetened Vanilla almond milk, 5-6 oz. filtered water, kale, spinach, two rounded tablespoons of ground flax seed, 2 Tbl spoons of raw Pepitas (shelled pumpkin seeds) one Tbl spoon apple cider vinegar, 1/2 teaspoon of turmeric with ground black pepper, 1/2 – 1 scoop of veggie protein powder (MRM makes a good one), rounded 1/2 cup of blueberries or tri-berry mix (blue, raspberries, black berries). optional, 1 generous Tbls of cocoa powder.




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  8. I always “eat” fruit smoothies. I don’t gulp them down, but take about 10 minutes. The reason for blending the fruits is because I can eat more fruits that way. (I don’t care too much for fruits (esp. hard fruits) and as for apples; most I don’t like; it takes me more than half an hour to eat one…)
    I blend different kinds of berries with several other fruits, like a banana, mango slices, etc. I also add some seeds (sunflower and pumpkin), oats and a few dried dates for extra sweetness. And a tablespoon of different teas/herbs. And I thought this was a healthy habit and was happy to have found a way to increase my fruit intake. In the past I tried green smoothies and even though I took the time to “chew” them and mix them well with saliva, I had a hard time digesting them: I kept burping and could not eat for hours. I have Dr. Greger’s book “How not to die” and I watch his videos and unless I’m badly mistaken I thought fruit smoothies is what he recommends. I’m Dutch and might have missed something or misunderstood. Either that or scientists first say this and now say something else…




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  9. Hey Dr.!
    I finally found someone who understands that fibers are removed in juicing a fruit. In fact, fiber is an
    essential nutrient for our bodies. Instead of taking juices, we should eat whole fruits to get all the
    nutrients it has to offer. This is certainly an informative piece of writing. Thanks for sharing Dr. Greger!




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