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Sip Smoothies Slowly

A famous study in 2000 compared the impact of soda versus jelly beans. Researchers had people add 28 extra spoonfuls of sugar to their daily diet in the form of jelly beans or soda. Then, they measured how many calories participants ate over the rest of the day to see if their bodies would compensate for all that extra sugar. For the jelly bean group, their bodies registered all the extra calories from the handfuls of jelly beans and they ended up eating less of everything else throughout the day. So, they ate pretty much the same number of calories before and after adding the jelly beans to their diet. But, for the soda group, despite all the added calories from the cans of pop they were drinking every day, they kept eating about the same amount. No wonder they gained weight after a month of drinking soda. Their bodies didn’t seem to recognize the extra calories when they were in liquid form and, therefore, didn’t compensate by reducing their appetite for the rest of the day.

What if we drink a smoothie for breakfast instead of eating a solid meal? Will our body think we skipped breakfast and make us so ravenous at lunch we’d eat more than we normally would and end up gaining weight? To answer this, we first have to determine if this solid versus liquid calorie effect is real. Soda and jelly beans don’t just differ by physical form; they have different ingredients. That’s a problem with a lot of these kinds of studies: They use dissimilar foods.

Take, for example, the study comparing liquid to solid breakfasts in my video Liquid Calories: Do Smoothies Lead to Weight Gain?. Researchers gave participants breakfasts of either fruit juices and skim milk or oatmeal with blueberries and apples. Not so surprisingly, study subjects were less hungry after the oatmeal. But, that may not be a solid versus liquid effect, as the breakfasts were comprised of completely different foods.

To test for a solid versus liquid effect, you’d have to use the exact same foods in two different forms. Finally, a study did just that. Researchers looked at what happens if you have a fruit salad with raw apples, apricots, and bananas with three cups of water to drink versus blending the fruit with two of the cups of water to make a smoothie and then just drinking the third cup of water. It’s the identical meal—one in solid form and one in smoothie form. What happened? People felt significantly less full after the smoothie, although it was the same amount of food and fiber. In smoothie form, it didn’t fill people up as much as eating fruit au natural.

Originally, we thought it was due to the lack of chewing. The act of chewing itself may be an I’ve-eaten-enough signal that you don’t get just by drinking. Researchers had people chew either 10 or 35 times per mouthful and eat pasta until they felt comfortably full. Those forced to chew 35 times per bite ended up eating about a third of a cup less pasta than those who only chewed 10 times per bite. So, there we have it: we have the proof of solid versus liquid effect and the mechanism. But, as so often happens in science, just when we have everything neatly wrapped up with a bow, a paradox arises.

In this case, the great soup paradox.

Pureed, blended soup—essentially a hot, green smoothie of blended vegetables—is more satiating than the same veggies in solid form. The same meal in liquid form was more filling than in solid form. So, it can’t be the chewing that has the satiating effect. In fact, there doesn’t appear to be a solid versus liquid effect at all, since cold smoothies appear to be less filling, but hot smoothies appear to be more filling. They are so filling that when people have soup as a first course, they eat so much less of the main course, that they eat fewer calories overall, even when you add in the soup calories.

How can we explain this paradox? Maybe pureed fruit is less filling than solid, but pureed vegetables are more filling? To test this, Purdue University researchers used apple soup. They mixed about a cup of apple juice with two cups of applesauce, liquefied it in a blender, and heated it up. If you have people eat three actual apples, they started out pretty hungry, but, within 15 minutes of eating the apples, they were hardly hungry at all. Drinking three cups of apple juice didn’t cut hunger much, but what about the apple soup, which was pretty much just hot apple juice with applesauce mixed in? The apple soup cut hunger almost as much as the whole apples, even more than an hour later. It even beat out whole apples for decreasing overall calorie intake for the day.

What’s so special about soup? What does eating soup have in common with prolonged chewing that differentiates it from smoothie drinking? Time. It took about twice as long to chew 35 times. And think about how long it takes to eat a bowl of soup compared to drinking a smoothie. Eating slower reduces calorie intake.

Alternatively, maybe we just imagine soup to be filling; so, it’s like a placebo effect. Feelings like hunger and fullness are subjective. People tend to report hunger more in accordance with how many calories they think something has rather than the actual caloric content. If you study people with no short-term memory, like the character in the movie Memento who couldn’t remember what happened more than a minute ago, they can overdose on food because they forgot they just ate, which shows what poor judges we are of our own hunger. It’s not just subjective effects, either. In a famous study called Mind Over Milkshakes, people were offered two different milkshakes, one described as indulgent, “decadence you deserve,” and the other a sensible, “guilt-free satisfaction.” People have different hormonal responses to them even though they were being fooled and given the exact same milkshake.

Finally, maybe it was just because the soup was hot, and warmer foods may be more satiating? How do we figure out if the solution to the soup mystery was time, thought, or temperature? If only the study we discussed earlier that had subjects eat either a fruit salad with three cups of water or drink the same exact foods in smoothie form had a third group—a liquid eating group, too. Well, it did!

Researchers also offered the fruit smoothie in a bowl to be eaten cold with a spoon. (Very un-soup-like.) So, if it were thought or temperature, the fullness rating would be down by the liquid drinking. However, if it was just the slowed eating rate that made soup as filling as solid food, then the fullness rating would be up closer to the solid eating rating—and it was exactly as high. The only real reason smoothies aren’t as filling is because we gulp them down, but if we sip them slowly over time, they can be just as filling as if we ate the fruits and veggies solid.

Wow, that study thought of everything. You don’t know the half of it! They also wanted to see if it would work with high-fat smoothies too. So, what, almond butter or walnuts? No, they used a liquefied fat smoothie of steamed pork belly.

I guess maybe sometimes smoothies can suppress your appetite :)

I have a whole series of videos on smoothies: Are Green Smoothies Good for You?, Are Green Smoothies Bad for You?, Green Smoothies: What Does the Science Say?, and The Downside of Green Smoothies.

For videos on weight gain, see Do Fruit & Nut Bars Cause Weight Gain?, Does Chocolate Cause Weight Gain?, Nuts and Obesity: The Weight of Evidence, and How Diet Soda Can Make Us Gain Weight. 

For weight loss, check out How Much Exercise to Sustain Weight Loss, Brown Fat: Losing Weight Through Thermogenesis, Boosting Brown Fat Through Diet, Eating More to Weigh Less, and Can Morbid Obesity Be Reversed Through Diet?

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.


36 responses to “Sip Smoothies Slowly

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  1. This is all good news to me. I’ve been eating a form of home-made warm blended mixed vegetable soup for many years. I do add some solid beans and cooked whole grains, so there is a little bit of “chewing” involved.

    Now off to have some Black Bean based artificial Turkey meat with friends and family. Happy Thanksgiving to all :-)




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    1. Happy Turkey day to you and your family :)

      The turkey did not die in vain but it is for us to says thanks to the kale and bean and herbs and all the plant foods that Mother Earth has given us for medicine.




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    1. @Tofues I’m curious what ingredients you use in your smoothies. I make 2 different large batch smoothies every weekend with each having a pound of dark leafy greens and each with about 15 different fruits, berries, and vegetables. Both of the smoothies provide me with a tall glass of smoothie every day for the rest of the week and I never have to worry about either of them going bad…




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  2. Dear Dr. Greger and Staff,
    Just wanted to take a moment to thank you and all the contributors here at Nutrition Facts for all the love and work you do for us.
    Now please take the rest of the day off and enjoy it with your family, after all it’s a holiday!!

    Mike




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  3. I discovered this years ago when I was eating a calorie restricted diet in preparation for bodybuilding competition. When I ate each carefully measured small meal very slowly I felt more satisfied afterward than if I had consumed the meal at normal speed. I attributed this to the fact that my stomach had more time to inform my brain that I was full (relatively). Alternately when I was a teenager I tended to wolf my food and many times overshot past being full resulting in quite a stomach ache.




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  4. I remember in your book you mentioned that cold water is more quickly absorbed than warmer water. Could this same principle be applied here? Wherein we tend to drink smoothies cold and soup hot, thus we’d be fuller from hot soup as we aren’t absorbing it as quickly. And if true could this affect be extrapolated to other features of smoothies and soups like blood sugar spikes. I could be totally off base, someone please correct me if I’m going on a tangent.

    As always love the content and thanks for the hard work :)




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  5. I would like to see the difference between slowly sipped smoothies, and the same food in solid form tested to see how it impacts blood sugars. With so many diabetics out there, and probably lots more people borderline, I think this is important to find out.




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  6. Ok, I seriously have to slow down my speed of drinking my smoothies. I made the MayoClinic green smoothie and just loved it. I added tumeric and amla powder. Yummo!

    Thanks for this great information, Dr. Greger and team!

    And Happy Thanksgiving to my American neighbors!

    A proud and healthy monthly supporter of Nutritionfacts.org




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  7. one of the nice things about smoothies is even people who are not on WFPB diet will accept a smoothie , especially if there is some fruit in it .
    our thanksgiving in Canada was about 5 weeks ago , and yes we broke down and had turkey , but i warned everyone next year it is going to be turkey again but a fake one , real ones are cruel .




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    1. Come on, it’s once a year. How can you spend Thanksgiving eating kale or sweet potato or faked turkey? Or I even read that some people eat nothing, i.e. fasting during Thanksgiving.

      You have to think that Thanksgiving is not just to eat and feast turkey but it is the time to say thanks, especially to the kale and bees who have to die for your foods, but it is also an occasion for family gathering. You have to know that less than 5% of the population are vegans and you cannot force the other 95% to eat kale or bean for Thanksgiving.




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      1. i don’t know Jerry I’ve made some really good vegan burgers , so maybe fake turkey might be pretty good too . dr ben kim from barrie ontario has a lot of good recipes that might interest you , as he sometimes uses tiny amounts of fish or the odd time egg , but mostly he uses whole plant based recipes . look for his korean pancakes yum .




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  8. About “The same meal in liquid form was more filling than in solid form”, I think it just due to the water that you add to your smoothie and it makes it expand in the stomach. Otherwise it should be the same, logically.

    Now there is a fallacy that eating too much will make you fat. Yes if you eat junk foods. But if you eat at least the Daily Dozen or eating enough healthy foods to get all of your nutrition and especially when you eat plant foods then you have to eat a lot to get enough protein and amino acids and certain vitamins and minerals and then you will find yourself eating all day long. I am dubbed “the guy who eats all the time” at work because there is so much foods I have to eat during the day to get my nutrition.

    So the least thing you want is that you are now full after consuming just one veggie smoothie in the morning and then skip meal for the rest of the day. Eating a lot of healthy foods and that includes healthy fats, does not make you fat. There is a misconception that eating too much will make you fat. That’s because people eat junk foods and sugar.

    Now getting full and having energy are two different things. I always start my day with a fatty meal with protein and that will give me energy for the rest of the day. Of course I include a lot of antioxidant and anti inflammatory foods to start my day. And eating fat will give me that filling sensation but I try not to let it stop me from eating what I need to eat. In another word, I usually don’t eat only when I am hungry but I eat at regular interval to consume the foods that I need.

    And I am not fat despite eating a lot. Zero fat on my body. Only muscle.




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    1. @Jerry Do you ever get bored spouting the same baseless beliefs over and over again? Half of what you just posted has been refuted multiple times by forum members who actually cite evidence in the literature. I would get so bored being you.




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      1. You need to ask TG if he has taken his statin drug. I don’t take any drug ever, even an aspirin. I only eat fat if you want to call it drug,




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        1. You have told us that you take heaps of supplements, Jerry. Sorry to break it to you but they are by definition drugs too. A drug is

          “A medicine or other substance which has a physiological effect when ingested or otherwise introduced into the body.”
          https://en.oxforddictionaries.com/definition/drug

          You take supplements because you believe that they have a physiological effect ergo you take drugs.

          And I haven’t taken a statin for 20 years or so. Since I started eating WFPB I haven’t needed to either.




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  9. A further thought occurs to me Jerry.

    If what you have told us about the number of supplements you take is correct, it is quite possible even probable that you take more drugs than anybody else using this site.

    I wonder if polypharmacy might explain the frequently addled nature of your posts? Polypharmacy is associated with increased risk of dementia and cognitive impairment. However, it is not clear if this is due to chance or if multiple drug use increases risk for cognitive problems. It is also possible that multiple drug use may cause symptoms that mimic cognitive impairment and/or dementia.

    For example “Polypharmacy was associated with cognitive impairment among urban community-dwelling older adults.’
    https://www.ncbi.nlm.nih.gov/pubmed/27628036

    Perhaps if you cut back on the pills and supplements, your cognitive difficulties might abate?




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  10. I’d read from Dr Arnold Ehret’s Mucusuless Diet Healing System (circa 1922) that consuming foods closer to body temperature caused the body to absorb the foods more readily into the bloodstream.. and that food (too hot or too cold) took more time for the body to absorb… perhaps there is a sensor in our systems that “gates” the right temperature for the bloodstream to absorb; hence satiating… interesting article, Doc .. thanks!




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