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Why it’s Better to Drink Green Smoothies With a Straw

A group of women were split into two groups and told to eat as much soup as they wanted, but half were given big spoons and told to eat quickly, while the other half were given small spoons and told to eat slowly. The slow group ended up feeling more satiated—despite eating less food. Prolonged meal duration can allow more time for our body’s own “I’ve-had-enough” signals to develop before too many calories have been consumed. It makes sense. After all, we evolved for millions of years before cooking, when undomesticated fruits and vegetables were much tougher and fibrous. Our body is built to expect us to take our time when eating.

What about when drinking? There weren’t any blenders on the African savannah. In smoothie form, you can drink fruits and vegetables at about two cups a minute—ten times faster than it might take to eat fruits and vegetables in solid form. Liquid calories can be consumed so quickly they can undermine our body’s ability 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. Blend all the smoothies you want, but sip them slowly for a half hour or so rather than gulping them down.

Even when sipped slowly, though, an all-fruit smoothie may not be as filling as eating a whole fruit, so the more greens you can add to your smoothie the better. You can also add ground flax seeds. As you can see in my video, The Downside of Green Smoothies, the thicker the smoothie, the less hungry you are one, two, and even four hours later—and flax seeds make for thick, milkshake-type smoothies. Researchers found that one tablespoon of flax seeds significantly suppresses appetite and calorie intake. You can give someone a meal two hours after the tablespoon of flax seeds, and they eat significantly less—all the while dropping their cholesterol in only one week when eating about a tablespoon of flax seeds each day.

The fat naturally found in flax seeds can also help maximize the absorption of fat-soluble phytonutrients. There’s a threshold for optimal absorption that can be reached with just about three walnuts worth of fat. If we’re trying to reduce added fats, a green smoothie with some nuts, seeds, or avocado can enable us 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 the lemon juice called for in Mayo Clinic’s basic green smoothie recipe (shown in the video), 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, and potentially improving arterial function in both the short- and long-term. Kiwifruit smoothies protect against DNA damage, and strawberry smoothies protect against inflammation. Of course, presumably, so would just eating greens, kiwis, and berries intact.

There’s been some concern expressed that drinking green smoothies would bypass the nitrate-reducing bacteria in the mouth, but our body’s way too smart for that; it pumps nitrate back into our salivary glands. Even if we deposited greens directly into our stomach with a tube, we’d still produce the nitric oxide so important for artery health.

Concerns have been raised that the oxalic acid in vegetables might increase kidney stone risk, but, as research shows, the opposite might be the case. (See How to Treat Kidney Stones with Diet.) So are there any downsides of smoothie consumption?

Whether with lemon juice or a lemon wedge, smoothies can be sour. Any time you’re eating or drinking something sour, you have to be careful about eroding the enamel on your teeth. Researchers found that 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, researchers 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. Drinking juice through a straw has less of an acidic effect than swishing it around in your mouth, so avoid swishing around mouthfuls of smoothie in your mouth. You also want to wait at least an hour before brushing so as not to brush your enamel in a softened state; rinsing your mouth with water after drinking smoothies can help rinse away some of the acids to protect your teeth.

One final caveat for smoothies: When I advocate green smoothies to boost fruit and vegetable consumption, I’m talking about whole food smoothies, not those made from juice or with added sugars—or human organs. Some women choose to consume their afterbirth. Though described as “replenishing and delicious,” the problem with eating one’s placenta is that one of the functions of the placenta is to filter out toxins, 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.

I have several videos on smoothies: 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?, and A Better Breakfast.

Was the concern about dental erosion new to you? See more in Plant-Based Diets: Oral Health, Plant-Based Diets: Dental Health, and Protecting Teeth from Hibiscus Tea.

What’s with that nitrate thing? See Don’t Use Antiseptic Mouthwash. So, What’s the Best Mouthwash? Watch to find out.

For more on fat-soluble nutrient absorption, check out an ancient video of mine, Forego Fat-Free Dressings?. And for more on oxalates and kidney stones, there’s How to Prevent Kidney Stones With Diet and How to Treat Kidney Stones with 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:


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.

22 responses to “Why it’s Better to Drink Green Smoothies With a Straw

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  1. Smoothies are such a great way to meet and exceed your fruit and veggie intake for the day! A boost of vitamins and minerals will give you the energy to get through the day (Thanks, B Vitamins!), antioxidant powers (Thanks, Vitamin C and Vitamin E!), and help you to make healthier choices throughout the day.

    Makes me wonder, though – of course acidic foods are bad for the enamel on your teeth, but is drinking a green smoothie much worse than chewing acidic fruits and veggies like oranges or tomatoes?

  2. Regarding acid beverages and tooth enamel, any Chemistry-minded folk know of a buffering agent that could be added to a drink without negative health and flavor implications?

  3. The buffering agent is saliva. There is no evidence that simply eating fresh fruits and veggies will permanently dissolve/damage enamel. There is evidence of remineralization of teeth after eating. The main thing to avoid is to put something like a lemon/orange/lime wedge over your front teeth and leave it there. This will damage enamel. Also, patients that have decreased salivary flow from medication, radiation treatment, Sjogren’s syndrome, etc, could be at increased risk of demineralization of their teeth.

    Dr. Ben

  4. If an acidic smoothie can lead to enamel erosion, would not the solution be to add additional ingredients that are alkaline in vitro, neutralizing the ph level? So, what foods can I use to do that? Thanks.

  5. Although as has been pointed out by Moderator Ben (see earlier comment) just drinking an citrus smoothie won’t necessarily lead to enamel erosion However, your idea that adding more alkaline foods to neutralize ph level would seem to make sense, in moderation, and fortunately, it is easily done by adding very healthy foods to your smoothie. Most of the foods listed, (nuts, fruits, vegetables) will make your smoothie taste even more delicious.

    1. I don’t see where in that mayoclinic linked article it says anything about those foods being alkaline in the mouth or ground up in a smoothie. It seems to me the fruits (apple and blueberry) are actually acidic.

  6. I make one smoothie for my nitric oxide, only. It is mixed dark ‘power greens’ I keep frozen till I blend with a large red beet, along with a tbsp or so of ground flax seeds. I also add a packet of natto to get extra vitamin K2 into me. There’s not even lemon or any other acid besides the green and beets, yet the smoothies were affecting my teeth, which I found interesting.

    I deal with the tooth problem by adding about half to three quarters tsp of baking soda to each smoothie. I used to get tooth sensitivity, now that has stopped since adding the baking soda.

  7. Great Article… as Always!!!
    For the past 7 months I have started my morning with a freshly squeezed whole lemon (organic when I can find them) in a 16oz. glass of filtered water: this I do “down” all at once. I then do rinse my mouth with (filtered) water in which to mitigate (hopefully) any acidic damage to my teeth… will now be sure Not to brush teeth within the hour afterward!!!
    Will now, also, add a wedge of lemon (organic): skin, Seeds and all to my green/berry smoothies (extra cancer prevention… Yay!) and be sure to sip slowly (1/2 hour) through a glass straw; will also be sure to add 3 walnuts (only 3 needed… Wow) and then, of course, follow by a rinse (again) of filtered water. Thx so much for these valuable tips!!!
    PS. First time posting a comment on your site, but long-time reader and admirer of your newsletters and website. jxo.

  8. Since discovering Dr, G, I have concocted a morning smoothie that consists of:
    Organic frozen berries (Costco)
    Organic greens — kale, spinach, and chard (Earthbound Farms)
    Ground organic flax
    Ground organic chia
    one banana
    handful organic red cabbage
    one celery stock
    4 oz blue diamond unsweetened almond milk
    4 oz Trader Joes tart cherry juice (unsweetened)
    one scoop Orgain organic plant protein power

    I know this is not what the doc recommends for a smoothie, but I think I am doing pretty well. What do you think doc? I think I check 6 or 7 boxes on the Daily Dozen.


    1. Stanwilson,

      Overall not shabby……. as Ben points out there are some processed products however, if this is what works for you….go for it ! Over time perhaps adding some real cherries, as an example, will power you on a bit further.

      Thanks for sharing your recipe.

      Dr. Alan Kadish Health Support volunteer for Dr. Greger

  9. Keep in mind that almond milk, cherry juice and plant protein are not “whole foods”. They are processed and important components that you need for health are removed.

    Evidence supports the recommendation that 5% of calories from protein are needed for optimum health. This can be obtained from a varied whole food plant based diet. Excess protein is toxic, so should not be added.

    Dr. Ben

  10. Hi.

    I have a question about smoothies. I am especially concerned about things which are described on this web site:

    Especially this part:

    Problems with Smoothies
    The problems with smoothies are two. First you don’t chew your food, and chewing is the first step in digestion that stimulates all the others. No chewing, no salivary enzymes, no pre-warning for the pancreas that food is coming. When the food in the smoothie, proceeds through the digestive tract, it may be mechanically broken down by the blender, but it has not been chemically treated by the usual salivary and other enzymes. I worry that the undigested nutrients can more easily ferment, leading to small intestine bacterial overgrowth, bloating, and abdominal discomfort.

    What is your opinion?

    Thank you.


    1. Rok,

      Can’t agree with you more….. chewing our food is both a necessary part of food ingestion and a normal stimulant toward the production of digestive enzymes.

      Juicing, dependent on the method, can strip the fiber content which clearly is another necessary element for our health. This will influence the microbiome and could result is issues of maldigestion and an imbalance of bacterial contents along with a higher glycemic load.

      Dr. Alan Kadish moderator for Dr. Greger

  11. Hi. I am new to smoothies. I have been making green smoothies. I am wondering how long will these keep fresh in the fridge. Also is the nutritional value degrading rapidly (so by day 2 in fridge all the benefit of the smoothie is gone?

    1. Hello David,

      While I am not aware of research on the specific percentages of nutrition that remain over time in smoothie form, once fruits/vegetables are blended, they have increased exposure to air, which can cause oxidation and nutrient loss over time. As a general rule, I would keep a smoothie in the fridge for up to 24 hours. It’s still okay to consume it beyond that timeframe as well, but the longer you leave it, the more oxidized it becomes. If it smells different or significantly changes in color, it is likely better off being discarded.

      I hope this helps,

      Matt, Health Support

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