Dr. Becky Maes - Is It Bad For You? Approved by Dr. Becky Maes

Are Green Smoothies Bad For You?



Short answer

Green smoothies can be nutritious and beneficial when made with whole, unprocessed ingredients and limited added sugars. It's important to differentiate between natural sugars in fruits and veggies, and added sugars which can contribute to health issues if consumed in excess. Oxalates in certain greens can pose risks for individuals susceptible to kidney stones. Balance is key—include low-GI fruits, fiber-rich greens, and avoid unnecessary sweeteners or additives.



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Long answer

Sugar Content in Green Smoothies: Natural vs. Added

When assessing the nutritional value of green smoothies, one critical factor that often raises concern is their sugar content. To navigate this aspect effectively, it's vital to distinguish between natural sugars found in fruits and vegetables and added sugars that might be included for extra sweetness.

Natural sugars are inherently present in the fruits that typically form the base of green smoothies. These sugars come with a package of beneficial nutrients such as vitamins, minerals, and fiber. For instance, an apple or banana can enhance the smoothie’s flavor while providing essential nutrients. The fiber content in these whole foods also helps to regulate the absorption of sugar into the bloodstream, preventing spikes in blood sugar levels.

On the other hand, added sugars refer to any sugars or sweeteners that are included in the smoothie recipe beyond what naturally occurs in the ingredients. These could include table sugar, honey, agave nectar, or syrups. Unlike natural sugars, added sugars contribute additional calories without beneficial nutrients and have been linked to various health issues such as obesity, heart disease, and diabetes when consumed in excess.

To make informed choices, look at the following comparison of natural vs. added sugars in typical green smoothie ingredients:

Ingredient Natural Sugar Content (per 100g) Common Added Sugars
Spinach 0.4g N/A
Kale 0.9g N/A
Bananas 12g Honey, Maple Syrup
Apples 10.4g Agave Nectar, Sugar
Almond milk (unsweetened) 0.6g Sugar, Syrups

It’s clear that whole fruits contribute natural sugars, while processed or flavored ingredients can introduce added sugars. To control sugar intake, it’s advisable to prioritize whole, unprocessed ingredients and be mindful of any unnecessary sweeteners. Moreover, the glycemic index (GI) should be considered, as ingredients with lower GI values release sugars more slowly into the bloodstream, beneficial for managing blood sugar levels.

Furthermore, research suggests that consuming whole fruits in a blended form, as opposed to juicing, preserves more of the fiber content, which can help mitigate the potential negative effects of sugar on the body. A study published in the Journal of the Academy of Nutrition and Dietetics highlighted that fiber intake is often inadequate in many diets and encouraged the consumption of whole fruits and vegetables as a method to improve fiber intake.

In summary, while green smoothies can be high in natural sugars, especially when made with a significant amount of fruit, the key is to achieve a balance. By incorporating more greens and vegetables, using lower-sugar fruits (such as berries or green apples), and avoiding unnecessary added sugars, green smoothies can remain a nutritious, health-promoting option in a balanced diet.

Oxalates in Leafy Greens and Kidney Health

One of the aspects that's often overlooked in the discussion about green smoothies is the presence of oxalates in leafy greens. Oxalates, also known as oxalic acid, are organic compounds found in a wide variety of foods, but they are notably high in certain types of leafy greens like spinach, Swiss chard, and beet greens—common ingredients in green smoothies.

While oxalates have their role in plant metabolism, in human diets they can bind with minerals to form compounds, such as calcium oxalate, which is one of the most common types of kidney stones. This raises potential concerns for individuals who are susceptible to forming kidney stones.

  • Impact of Oxalates on Absorption of Nutrients: The binding nature of oxalates can interfere with the absorption of minerals, particularly calcium and magnesium, which could potentially lead to deficiencies despite a seemingly nutrient-rich diet.
  • Risk for Kidney Stone Formation: People with a history of kidney stones, especially calcium oxalate stones, need to be cautious. Regular high consumption of high-oxalate greens in smoothies can increase the risk of stone formation.

However, it's important to recognize that not everyone is equally sensitive to oxalates. Most people can consume moderate amounts of high-oxalate foods without any issues. The body usually handles the natural levels of oxalates found in food quite well, provided that the person has no pre-existing issues with kidney stone formation or absorption of minerals.

How to Enjoy Green Smoothies Safely:

  • Variety is key — Rotate your greens daily or weekly to ensure a wide range of nutrients and avoid overconsumption of oxalates.
  • Boiling high-oxalate greens can reduce their oxalate content significantly, although it's not a common method for greens intended for smoothies.
  • Incorporate calcium-rich ingredients into your smoothies, like yogurt or kefir, which can bind to the oxalates in the gut and may help reduce the risk of stone formation.
  • Stay hydrated — Drinking fluids, especially water, can dilute the oxalates and reduce the risk of kidney stones.

Studies indicate that dietary factors, including intake of fluids, calcium, and oxalate, play a role in kidney stone formation. According to the American Journal of Clinical Nutrition, adequate intake of calcium, particularly from dietary sources, may actually lower the risk of stone formation compared to a diet low in calcium 1. Thus, incorporating calcium into smoothies could be beneficial while consuming foods with high levels of oxalates.

It's always recommended for individuals with a history of kidney stones or other renal issues to consult with a healthcare provider before making green smoothies a regular part of their diet.


  1. Curhan, G. C., Willett, W. C., Knight, E. L., & Stampfer, M. J. (2004). Dietary factors and the risk of incident kidney stones in younger women: Nurses' Health Study II. Archives of Internal Medicine, 164(8), 885–891.

Impact of Green Smoothies on Blood Sugar Levels

The concern around green smoothies and blood sugar levels stems from the variable content of fruits and vegetables blended in these drinks. It is essential to understand the glycemic index (GI) and glycemic load (GL) of ingredients used in green smoothies to assess their impact on blood sugar levels.

Glycemic Index and Glycemic Load Considerations

The GI measures how quickly a food causes blood sugar levels to rise. Foods with a high GI score, such as processed sugars, cause a more rapid increase in blood sugar. Conversely, low-GI foods like non-starchy vegetables result in a slower, more controlled rise in blood sugar. The GL is an extension of the glycemic index, taking into account the serving size of the food. This is critical in smoothies, as the combination of fruits and vegetables can alter the overall GL of the drink.

Most leafy greens that form the basis of green smoothies are low in carbohydrates and have a negligible effect on blood sugar. However, the addition of high-GI fruits or sweeteners can significantly increase the smoothie's potential to spike blood sugar levels. Therefore, choosing low-GI fruits such as berries, cherries, or apples can help maintain a healthier blood sugar curve.

Balancing Ingredients for Blood Sugar Management

  • Include high-fiber greens such as spinach, kale, and broccoli to slow digestion and stabilize blood sugar spikes.
  • Opt for fruits that have a lower glycemic impact like berries, apples, and pears rather than high-sugar choices like bananas or mangoes.
  • Add protein sources like Greek yogurt, nuts, or seeds to help modulate the blood sugar response.
  • Be mindful of added sweeteners - use natural options like stevia or monk fruit, or better yet, avoid them entirely.
  • Portion control is crucial - even with healthy ingredients, large servings can lead to higher blood sugar levels.

Scientific Research on Blood Sugar Impact

Research has shown mixed results on the effects of smoothies on blood sugar levels. A study published in the Diabetes Care journal suggests that liquid carbohydrates, such as those found in smoothies, tend to increase blood sugar more rapidly than solid carbohydrates. However, the inclusion of dietary fiber as present in leafy greens and some fruits can attenuate this response. It's evident that the ingredients and their proportions significantly influence the blood sugar impact of a green smoothie.

Furthermore, an observational study highlighted in the British Journal of Nutrition reported that high intake of leafy greens is associated with a lower risk of type 2 diabetes. This suggests that incorporating greens into one's diet, possibly through smoothies, may have long-term benefits for blood sugar management when executed wisely.

Individuals with diabetes or insulin resistance should closely monitor their response to green smoothies and consult with healthcare professionals to tailor ingredients that align with their dietary requirements.

In conclusion, while green smoothies can potentially impact blood sugar levels, careful selection and balance of ingredients can mitigate these effects and fit into a healthy, balanced diet. Always consider the individual components of your smoothie and how they interact to affect the overall blood sugar response.

The Role of Fiber in Green Smoothies and Digestive Health

Fiber plays a critical role in our overall health, particularly in the function of the digestive system. When it comes to green smoothies, they're often lauded for their high fiber content, thanks to the inclusion of fibrous vegetables, fruits, and sometimes, additional ingredients like seeds or nuts. Let's illuminate how fiber in green smoothies impacts digestive health.

Dietary Fiber: Soluble and Insoluble

Before we delve into the effects of green smoothies, it's important to recognize the two types of dietary fiber:

  • Soluble Fiber: This type dissolves in water and can help to lower blood cholesterol and glucose levels. It's found in oats, peas, beans, apples, citrus fruits, carrots, barley, and psyllium.
  • Insoluble Fiber: This type promotes the movement of material through your digestive system and increases stool bulk, benefiting those with constipation or irregular stools. Whole-wheat flour, wheat bran, nuts, beans, and vegetables are good sources of insoluble fiber.

Most green smoothies incorporate a combination of these fibers, offering a balanced approach to digestive health.

Impact of Fiber from Green Smoothies

Eating whole fruits and vegetables is the best way to get your fiber, and green smoothies can contribute to that. The blending process may reduce the size of the fiber particles but doesn't significantly diminish their beneficial properties.

  • Regularity and Constipation Relief: The insoluble fiber in green smoothies aids in adding bulk to stool, which can help maintain regular bowel movements and prevent constipation.
  • Prebiotic Effects: Certain fibers in green smoothies act as prebiotics, feeding beneficial gut bacteria, which is key for a healthy microbiome. A study published in the Journal of Nutrition suggests that prebiotic fibers can improve gastrointestinal health by enhancing the growth of beneficial bacteria.
  • Weight Management: High-fiber content from smoothies can lead to a feeling of fullness, possibly helping with weight control. A systematic review and meta-analysis featured in the Annals of Internal Medicine concluded that people who increased their fiber intake tended to eat less and lose weight.

Fiber Content in Typical Green Smoothie Ingredients

A close look at common green smoothie ingredients uncovers a variety of fiber sources:

  • Leafy Greens: Spinach, kale, and collard greens are fiber-rich and form the base of many green smoothies.
  • Fruits: Apples, pears, and berries add a sweet touch along with a soluble fiber boost.
  • Seeds: Chia seeds, flaxseeds, and hemp seeds are not only fiber-rich but also contain omega-3 fatty acids and protein.

Maximizing the Benefits

To ensure you're getting the most out of the fiber in your green smoothies:

  • Variety: Rotate your ingredients to get a mix of soluble and insoluble fibers as well as a broad spectrum of vitamins and minerals.
  • Whole Foods: Go for whole fruits and vegetables rather than juices to maximize fiber content.
  • Limit Processing: Excessive blending can break down fibers too much; blend just enough to break down the big pieces.
  • Moderation: Even though green smoothies are beneficial, they shouldn't be your only source of fiber; ensure a balanced diet.

Identifying individual tolerance is vital. For some, a high intake of fiber, especially if increased suddenly, can lead to digestive discomfort like gas or bloating. It is generally recommended to increase fiber intake gradually and monitor the body's response.

Ultimately, green smoothies can support digestive health through their varied fiber content, but attention to ingredient quality, variety, and individual digestive tolerance is key. Including green smoothies as part of a balanced diet can provide a convenient and tasty way to boost your fiber intake, enhancing overall digestive wellness in the process.

Nutrient Absorption: Benefits and Possible Inhibitors in Green Smoothies

Green smoothies can be packed with vitamins, minerals, fiber, and antioxidants, making them a seemingly ideal choice for enhancing nutrient intake. A primary benefit of consuming nutrients in smoothie form is the blending process, which can break down plant cell walls, thereby making some nutrients more bioavailable than they might be in whole vegetables and fruits. This can often aid in digestion and absorption.

For example, blending leafy greens like spinach or kale results in the release of iron and calcium, two important minerals that are essential for our health. Moreover, the vitamin C content from fruits like oranges or strawberries can improve the absorption of iron, which is especially advantageous for those with higher iron needs or individuals following vegetarian or vegan diets.

However, certain components in green smoothies might inhibit nutrient absorption. Components such as:

  • Oxalates: Found in high amounts in spinach, chard, and beet greens, oxalates can bind to minerals like calcium and lead to poor absorption.
  • Phytates: Present in seeds and grains, which are sometimes added to smoothies for protein and texture, phytates also have the ability to bind minerals and inhibit their absorption.
  • Fiber: While beneficial for the digestive system, an excessive amount of fiber can reduce the absorption of some nutrients by binding to them before they can be absorbed.

Moreover, the impact of blending on the fiber structure of fruits and vegetables raises some concern. According to a study published in the Nutrition Journal, the severing of the food matrix can sometimes affect the rate at which sugars are released and absorbed, potentially impacting blood sugar levels and satiety.

Consuming a well-balanced smoothie that combines both greens and a source of healthy fat, such as avocado or nuts, can improve the absorption of fat-soluble vitamins (Vitamins A, D, E, and K). Meanwhile, adding a protein source like Greek yogurt can make a smoothie more satiating and reduce the rapid spike in blood sugar levels.

It's important to balance out the components of your green smoothie and consider these possible inhibitors, especially if you have specific health concerns, such as kidney stones, which could be exacerbated by high levels of oxalates. Consulting a healthcare provider or a nutritionist can provide personalized guidance to ensure that green smoothies contribute positively to your diet without hindering nutrient absorption.

Balancing Ingredients for a Healthy Green Smoothie

Green smoothies have become a trendy choice for those looking to infuse their diets with a concentrated dose of nutrients. While they can be incredibly beneficial, striking a balance in the ingredients is crucial to ensure that your smoothie remains both nutritious and conducive to your overall health. Here's how to create that perfect balance:

Vary Your Greens

Rotating your greens avoids the build-up of anti-nutrients and provides a spectrum of vitamins and minerals. Spinach, kale, and Swiss chard are great, but also consider romaine, parsley, or collard greens for diversity.

Be Mindful of Sugar Content

While fruit enhances flavor and adds natural sweetness, it's essential to be aware of the sugar content. Limit fruit to a one-cup serving per smoothie and opt for low-glycemic options like berries, green apples, or a small banana. A study published in the Nutrition Journal found that low-glycemic index foods could help in maintaining blood sugar levels, which is important for preventing energy crashes and managing weight.

Include Healthy Fats

Adding a source of healthy fats, such as avocado, nuts, seeds, or a swirl of flax or chia seeds, not only contributes to creaminess but also helps in the absorption of fat-soluble vitamins. According to research in the American Journal of Clinical Nutrition, fats can increase the bioavailability of certain nutrients in vegetables.

Don’t Forget Protein

Protein is essential for a balanced smoothie, aiding in muscle repair and satiety. Consider plant-based proteins like pea protein, hemp seeds, or Greek yogurt if you don't have dietary restrictions. The Journal of the American College of Nutrition supports the inclusion of protein in meals to promote muscle synthesis and metabolic regulation.

Limit Added Sweeteners

Even 'healthy' sweeteners like honey or agave can contribute to excessive sugar intake. If additional sweetness is necessary, opt for natural sources such as a small amount of 100% pure maple syrup or stevia. The World Health Organization recommends reducing the intake of free sugars to less than 10% of total energy intake, underscoring the importance of moderating sweeteners.

Enhance with Superfoods

While not essential, adding superfoods like spirulina, chlorella, or wheatgrass can boost the nutrient profile significantly. These superfoods are packed with antioxidants, chlorophyll, and additional vitamins and may have detoxifying properties. A study by the Journal of Chiropractic Medicine found that chlorella intake resulted in noticeable reductions in cholesterol levels.

Choose The Right Liquid

The liquid base of your smoothie affects its overall calorie and nutrient makeup. Water is always a safe, no-calorie option, while plant-based milks like almond or coconut milk offer a dose of vitamin D and calcium with lower calories than cow's milk. For those who prefer dairy, opt for skim or 1% milk to keep the fat content in check.

By adhering to these guidelines, you can create a green smoothie that is not only a delight to your taste buds but part of a truly healthy, balanced diet. Remember, the key to a nourishing green smoothie lies in the quality and proportion of ingredients you blend together.

Frequently asked questions

Overconsumption of spinach or kale in green smoothies can lead to an excessive intake of oxalates, which are naturally occurring compounds that can bind with minerals and potentially form kidney stones in susceptible individuals. It's crucial to rotate your greens to prevent the buildup of oxalates and ensure a diverse intake of nutrients.

While green smoothies are a great way to incorporate fruits and vegetables into your diet, they shouldn't completely replace whole fruits and vegetables. Whole foods provide chewing resistance, which can aid in satiety, and the act of chewing also produces saliva, which is beneficial for oral health. Additionally, whole produce may contain more fiber, as the blending process can sometimes break down fiber into smaller pieces.

The liquid base of your green smoothie can significantly affect its calorie, nutrient, and sugar content. Water is calorie-free and doesn't add sugars, while unsweetened plant-based milks offer added nutrients such as calcium and vitamin D with minimal calories. Using fruit juices or sweetened milks can add unnecessary sugars and calories, which could affect your overall dietary goals.

For vegetarians or vegans looking to add protein to green smoothies, consider plant-based protein sources such as pea protein, hemp seeds, chia seeds, or tofu. These options provide a good balance of essential amino acids and are also rich in other nutrients. Nut butters, like almond or peanut butter, can also serve as a tasty protein boost.

Ask a question about Green Smoothies and our team will publish the answer as soon as possible.

Possible short-term side effects

  • bloating
  • gas
  • blood sugar spikes

Possible long-term side effects

  • nutrient deficiencies due to oxalate absorption
  • increased risk of kidney stones
  • insulin resistance

Ingredients to be aware of

  • added sugars
  • oxalates
  • phytates
  • excessive fiber
  • high-gi fruits
  • artificial sweeteners


  • high nutrient intake
  • blood sugar management with low-gi fruits
  • weight management
  • digestive health improvement
  • increased fiber intake
  • muscle repair and satiety
  • antioxidant intake

Healthier alternatives

  • low-gi fruits
  • natural sweeteners like stevia
  • healthy fats
  • lean proteins
  • varied leafy greens
  • plant-based milks
  • superfoods like spirulina

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Thank you for your feedback!

Written by Diane Saleem
Published on: 01-17-2024

Thank you for your feedback!

Written by Diane Saleem
Published on: 01-17-2024

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