Green Smoothies are Bad for You!

Well, that’s the rumor anyways.  In truth, I’m not at all convinced that green smoothies are bad for you.

While researching the “cons” – the downside – of green smoothies, I came across several objections ranging from minor to alarmist.  Are green smoothies really bad for you?  My conclusion is no, but read on for further details and judge for yourself!

In our previous post in this series, we covered the health benefits of green smoothies.  Now it remains for us to perform due diligence and explore the dark underbelly of this food trend to see if there are any lurking dangers that we need to be aware of. Just like any diet, supplement, or exercise regimen, we should always look at the big picture before diving in head first – then we will be better prepared to maximize our results!

Objections to green smoothies include the following:

  1. Blending food oxidizes the nutrients, so the nutritional value is destroyed.
  2. Green smoothies bypass our “chewing” enzymes, so we don’t get optimal nutrition from the food.
  3. Green smoothies let us easily overeat, so we consume too much food in a single sitting.
  4. Mixing food types is bad for digestion, so smoothies cause poor nutrient absorption.
  5. Green smoothie diets are expensive – fresh produce entails high cost.
  6. Green smoothies are high in Oxalates, so they cause kidney stones – or worse!

I’ll cover these point-by-point below!

1.  Blending food oxidizes the nutrients

OxidationThe assertion here is that when you blend food you are simultaneously breaking open cell walls and mixing the food at high speed, introducing millions of tiny air bubbles to those nutrients.  The oxygen in those air bubbles will then react with the nutrients, oxidizing it and ruining its nutritional value.

Oxidation is a chemical reaction, whereby an oxidizing agent (oxygen, in this case) reacts with another molecule – stealing an electron and forming an oxide.  The most common daily example is rust.  To horribly oversimplify, iron + oxygen forms iron oxide (rust).  Oxidation is a reaction that requires A) exposure to oxygen and B) some amount of time.

My objections to this assertion are based on a few points:  Oxygen is found in relatively low concentrations in the air around us (roughly 21%), oxygen is not the most agressive oxidizing agent known to man, smoothies are generally fluid environments (less exposure to oxygen in the air), the time between creation and consumption of a smoothie is relatively short so the time allowed for oxidation is also short.

Two simple observations backup my objections:  taste and appearance.  The taste and appearance of a green smoothie are as you would expect, relative to the vegetables involved.  Oxidation is a chemical change and therefore should change the appearance, the taste or both if it is truly happening on a large scale.
Even if some oxidation does occur, those nutrients would be trapped within cellulosic material if we did not blend them – so they would still be inaccessible to our bodies.  At least blending them gives the possibility to access those nutrients.

Verdict:  Blending green smoothies does not oxidize nutrients enough to be a concern.

2.   Green smoothies bypass our “chewing” enzymes

Importance of Chewing FoodThere may be something to consider here.  It is true, after all, that if you make a very creamy or fluid smoothie, then you do not chew it – you drink it.  Generally speaking, chewing food mixes enzymes in our saliva with the food that we are eating.  The act of chewing also helps to “prep” the rest of the digestive system to let it know that food is coming.

When drinking a green smoothie, you may access some of the enzymes in your saliva as it passes by – but not as much as chewing it.  One question I would have is how many of those enzymes are needed when the food has already been physically pre-processed by the blender before consuming it.  Clearly the purpose of those enzymes would be to start breaking food down – a process we have already done extensively via the mechanics of the blender.

Two other observations relate here as well.  Infants do not chew their food, and especially in the case of vegetable baby food, they are consuming similar food to what you would find in a green smoothie.  Mass-produced baby food seems to produce acceptably healthy children – and homemade baby food is often similarly prepared.  Another observation is that our rushed society generally discourages proper chewing in any case.  Most of us are so rushed at lunch that we choke down some food and get back to work.  We do not chew 20 or 40 times per mouthful (or whatever the recommended number of “chews” is nowadays).  So as a society we probably lack proper chewing enzymes when we eat regardless.  In that case, blended food has the edge.

Verdict:  This concern may be somewhat valid.  If you wish to minimize it, my suggestion is to take your time and enjoy your green smoothie.  Taste each mouthful before swallowing and that should give more exposure to the enzymes in your saliva.  Or better, if your smoothie consistency leaves some chunks in the food, your reaction is to instinctively chew those before swallowing – making this a non-issue.

3.  Green smoothies let us easily overeat

Overeating due to SmoothiesThis concern is one that applies to any food that one can eat too fast.  A smoothie allows us to consume a large volume of food/drink in a single sitting.  Really this is no different than drinking too much of anything else…. sports drinks, fantastic seasonal beers, or whatever our fancy may be.  Anything that tastes good and is in fluid form is easy to consume in large amounts.

The keys here are experience and self-control.  The first few times we consume a green smoothie, we might overdo it and find ourselves stuffed.  Merely use that experience of being full to help remember to use less water and less veggies next time.  In addition, if we are dieting and know approximately how many calories (or how many servings of vegetables) we need, the practice of some self-control should help prevent overeating.  Obviously this is easier said than done – if the problem is due to an indulgent lack of self-control, then the green smoothie is not the problem and any food would also allow us to overdo it.

One last consideration is that “overdoing it” with vegetables is difficult for most of us.  Vegetables are low calorie foods so it would take a large amount to overdo it with calories.  In addition, for many of us, we consume far too few (almost no) vegetables as part of our standard American diet.  So consuming beyond the daily recommended vegetable allowance in one setting would also be difficult.

Verdict:  Plan ahead to know which daily meals will include a green smoothie, know what ingredients will be included, and use experience to teach what water/ingredient amounts work best!

4.  Mixing food types is bad for digestion

Fruits, vegetables, nutsIn the world of food consumption, there are apparently some purists that believe certain food types should not be mixed in a given meal because our digestive system needs to process them differently – taking longer to process some foods than others in order to extract the optimal amount of nutrition from each.  I personally had never stopped to consider this possibility before!

So, the assertion goes that mixing things like fruit, seeds or nuts with vegetables in a green smoothie is just causing all of those nutrients to rush past our digestive guards on their way out the door, leaving our bodies unable to identify which ones need to more time to process.

I think the thing to keep in mind here is that our body automatically determines the type of processing necessary for the foods we consume (it has to – we don’t consciously do this).  So it must determine these digestive needs based on the physical structure of the food that needs to be broken down, as well as the nutrient load it finds present in the food.

A green smoothie is a homogenous mixture, both physically and with regards to nutrient content.  Even nuts and seeds are broken down into relatively fine portions.  Our bodies should be able to process this homogenous mixture as a single entity without much confusion, and I think that the experiences of people who consume green smoothies would attest to this.  In the short term, people tend to experience energy from the easily accessed nutrition.  In the long-term, they experience health benefits associated with better diet.

Verdict:  The nature of a green smoothie negates any concern about mixing food types, as it relates to digestive processing differences.

5.  Green smoothie diets are expensive

One Hundred Dollar BillYes, diets of fresh vegetables can be expensive depending on where you live and the time of year.  This concern relates to any diet that requires fresh produce, so it is not strictly a complaint against green smoothies.  However, since green smoothies allow you to eat more vegetables than you might otherwise, it is a valid concern for many of us.  I certainly cannot afford fresh greens every day (especially organic), so I assume that’s true for many of you as well.

The solution for those of us on a budget?  Frozen vegetables.  I tend to pre-mix my smoothie ingredients in advance, which means I freeze them anyways (see green smoothie convenience benefit number one).  Frozen vegetables allow us to include a large variety in our green smoothie at little expense.  The nutrient value may be somewhat less than fresh vegetables, but still better than the canned/cooked variety.

The only ingredient I keep fresh for daily use are the spinach, romaine lettuce, kale, etc that I use as the “leafy green” base of the smoothie.  Everything else is of the frozen, budget variety.  During the winter months, I may vary that strategy somewhat as well.

Verdict:  Buying frozen vegetables and ingredients for your green smoothies can help to drastically reduce their cost, and make for convenient storage and meal prep.

6.  Green smoothies are high in Oxalates!

Calcium Oxalate

Calcium Oxalate

The terms Oxalate and Oxalic Acid are often used interchangeably with regard to foods – especially when discussing the cons of a diet that contains high amounts of leafy green vegetables.  To clarify, oxalic acid is a naturally occurring compound found in both plants and animals.  It is found in our own bodies, due to consumption of certain foods and due to its creation by our own bodies.  When oxalic acid binds with minerals such as calcium, it creates oxalates such as calcium oxalate – a major component of kidney stones.

In most instances, our bodies evacuate this excess oxalate in our urine, but in certain individuals these oxalates build up internally to create kidney stones.  One source that I read even mentions that oxalate build-up elsewhere in the body (not just the kidneys) could be a contributing cause of fibromyalgia, a chronic disorder characterized by widespread musculoskeletal pain.

What foods contain a high amount of oxalic acid?  Leafy greens are one culprit, including spinach, swiss chard, beet greens, collards, parsley, okra.  Other vegetables, nuts and fruits also contain noticeable levels.

In light of our topic here, does eating green smoothies cause kidney stones?  Kidney stones are caused by a number of factors including genetics, diet, hydration and others.  Diet is only one portion of this.  In fact, low-oxalate diets are usually medically prescribed only for people with a high-risk of kidney stones.  High risk individuals would include people who have had kidney stones in the past, or people with some form of Hyperoxaluria – a disorder that affects only a small portion of the population.

The medical profession seems to agree that the health benefits of eating vegetables containing high amounts of oxalic acid far outweigh any associated risks.  Some individuals even assert that it is the cooking of such foods that can cause problems in our bodies, because cooking the vegetables changes the chemical make-up of the oxalic acids into a form that our bodies cannot handle.  This would make raw vegetables, and green smoothies, the healthy choice for consuming your green vegetables.

Verdict:  Consuming green smoothies as part of a diet gives more benefit than risk.  Continue to enjoy them, but avoid going to extremes (they should not become your entire diet, for example).  If you are concerned, rotate your ingredients so you do not always consume the same vegetables from week to week.  If you are very concerned, consult your doctor.  Otherwise, continue to enjoy your green smoothie meals!


After weighing the pros and cons of green smoothies, I personally feel that the health and convenience benefits of green smoothies far outweigh any of the cons listed here.  I certainly plan on continuing them as part of my diet, enjoying it while I do!

How about you?  Feel free to read through the items I have listed here, refer back to the previous post, read through the references listed below, do your own research on- or off-line – and come to your own conclusions.  What do you think?  Did I miss anything in my assessment?  Reply in the comments below!


Image Credit:  Calcium Oxalate from the Wikimedia Commons, via the Creative Commons Share Alike 2.5 Generic license.


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