Green smoothies are perceived as the "healthy" version of fruit smoothies – but are they really so healthy? Detractors say green smoothies are:
• high in calories
• high in sugar
• low in nutrients including fibre, due to the blending process
• a source of toxic oxalates and goitrogens
I've been consuming two green smoothies every day since 2012 – so I suppose I'm a bit biased.
I have had a few health problems during that time, but I don't blame my green smoothie habit for them. I've managed to overcome these health problems, while continuing to drink two green smoothies every day.
What is a green smoothie?
Green smoothies are made from fruit and green vegetables blended with water. Simple as that. The recipes can be as varied as the recipe for a salad, as long as they contain fruit, greens and water and are not cooked.
Some people add yogurt or chia seeds, or even a pinch of cayenne! (I've tried adding cayenne to a green smoothie, and it's much nicer than you might think.)
I've fallen into a bit of a routine with my green smoothies – simply because this is a basic recipe that I love. It makes two green smoothies, or about 800-900ml:
• 2 medium-sized bananas, peeled
• 1/2 a mango OR 1/4 pineapple, peeled
• 1 medium-sized orange OR apple
• 1 handfuls of spinach OR kale
• 400-600ml water
Blend it all up in a powerful blender. I have an industrial-size Blendtec, but a Nutribullet will do. Basically, the more powerful your blender is, the smoother and less lumpy your green smoothie will be.
Green smoothies might not be everybody's cup of tea, but they are much more delicious than they look – depending on how they are made, of course.
Sometimes I vary the recipe a bit. Occasionally – if I run out of greens, for example – I add a handful of frozen berries instead.
Adding berries to a green smoothie can improve blood sugar control.
In fact, scientific research indicates that drinking blended berries (ideally blackcurrants) actually improves blood sugar control, so if you're concerned about the possibility of green smoothies giving you a blood sugar spike, you could substitute mixed berries for the pineapple or mango in my green smoothie recipe.
Green smoothies tend to be quite high in natural sugar. My recipe contains 55g of sugar in total; 26.5g in each smoothie. However all of this sugar comes from fruit, and it is consumed along with fibre, which helps slow it down on its journey through the gut.
If you substitute berries for the mango/pineapple and orange, the total sugar content falls to about 35.5g for both smoothies, or 18g in each one.
I generally avoid eating any refined sugar unless it's my birthday, Christmas or after a big hillwalk, and a recent blood sample showed my blood sugar levels to be healthy.
So are green smoothies healthy or not?
Not particularly high in calories
The green smoothies I make total about 350 calories, so each one is about 175 calories, which I don't think is a large amount. I usually have my green smoothies for lunch, with some nuts, and that keeps me full until dinner time.
High in vitamins and minerals
Green smoothies are high in vitamins and minerals, supplying more than the US and UK recommended daily amounts (RDA) of vitamin A, vitamin C, vitamin K, and manganese. They are also high in many B vitamins, folate, magnesium and copper, AND they supply about 6g of protein.
This is the case even if nutrient loss from blending is taken into account, because the vitamin and mineral content of fruit and greens is so high compared to many other types of food.
Two green smoothies made with my recipe can also contain half the recommended daily amount of dietary fibre. I find that if I consume more than two green smoothies a day, my digestive system goes into overdrive, but two seem to provide the perfect amount of fibre to keep my bowels functioning well.
Does blending destroy the nutrients?
It's likely that some of the nutrient value of green smoothies is lost when they are blended, but probably nothing like as much as the 85-92% of nutrients that Dr Brian Clement of the Hippocrates Health Institute has claimed is lost when smoothies are blended for 90-120 seconds. Certainly, I know no one who blends their smoothies for this length of time. My Blendtec takes 30 seconds to blend my smoothies.
Korean scientists who compared the nutrient content of blended and juiced fruit blended apples, pears, persimmons and mandarin oranges for an astonishing three minutes at more than 20,000 rpm, still found that the blended juice contained significant amounts of polyphenols and flavonoids.
The research showed that although levels of ascorbic acid were lower in the blended apples, pears and oranges than in the juiced fruits, the blended persimmons had higher levels of ascorbic acid. All the blended fruits had significantly higher concentrations of citric and malic acids than the juiced fruit.
The research also found that total polyphenols and total flavonoids were significantly higher in blended persimmon and mandarin orange juices, but not in the other fruits.
Blended persimmon juice had more polyphenols and flavonoids than other blended fruits.
Could green smoothies cause iodine deficiency?
Kale is a goitrogenic and if eaten raw in large amounts it can impair the absorption of iodine, which can lead to thyroid problems. Other goitrogenic foods include other cruciferous vegetables such as cauliflower and broccoli, as well as soy products, flaxseeds, millet, peanuts, peaches, pears, pine nuts, spinach, sweet potatoes, and strawberries.
As long as your iodine intake is sufficient, there is no need to avoid any of these foods.
What about the effects of oxalates?
Raw kale contains oxalic acid which, if consumed in large amounts, can bind with other minerals to cause inflammation, kidney stones and gout. The list of foods containing oxalic acid includes spinach, peppers, sweet potato, squash, pumpkin, chocolate, nuts, berries, tea and coffee.
Oxalic acid is also found in coffee and chocolate.
Most of the oxalic acid in these foods is likely to be excreted by the body, with less than two percent being absorbed. Research suggests that the gut bacterium Oxalobacter formigenes helps to prevent conditions such as kidney stones by degrading oxalate activity. But this bacterium can be inhibited by the action of certain antibiotics, including clarithromycin and doxycycline.
So if you have a healthy gut, the small amount of oxalates consumed in green smoothies is unlikely to be problematic.
Hydration
Green smoothies are very hydrating, and as a regular hillwalker, I always take one with me when I climb a mountain.
Why not just eat the fruit?
Maybe it would be healthier to eat the ingredients of a green smoothie completely fresh and unblended, in a fruit salad perhaps.
That's a lot of fruit and raw greens to eat each day!
But how many people would actually do that – eat that amount of raw fruit and greens every day? People who have a high raw or totally raw lifestyle probably do, but most people don't eat anything like that amount of fresh fruit or vegetables.
As a result, many people – especially those who eat a lot of processed food – are deficient in nutrients such as magnesium, vitamin A, vitamin C and fibre.
As long as I have my two green smoothies each day, I know that I'm getting at least most of my RDA of the above-mentioned vitamins and minerals.
How to make green smoothies even healthier
• Sip them slowly to avoid a blood sugar spike, rather than glugging them back all at once.
• Add healthy fats such as linseeds or avocado, to improve nutrient absorption.
Adding healthy fats such as avocado flesh to a green smoothie can improve nutrient absorption.
• Drink your smoothies through a straw and/or rinse your mouth out with water after drinking, to mitigate the effects of acid in fruit which can lead to tooth enamel decay.
Convenience
Fruit salads are great, but if you want to eat them on the move, you need a salad box and a fork, while whole fruit, such as bananas or apples, can get squashed and dirty if you put them in your bag – unless you carry them in a bulky container.
Green smoothies can be carried around easily in a bottle. For me, they are the ultimate healthy convenience food.
Other sources
Plant-based diets: A Physician's Guide by Julieanna Hever, MS, RD, CPT
Green Smoothies: What Does the Science Say? by Michael Greger M.D. FACLM
Are There Toxins In Your Kale? – The Telegraph