Contact with too many naturally occurring acids, like the ones found in fruit, has been proven to cause dental erosion,
A 2013 study found that smoothies containing fruits like strawberries, bananas, cranberries, blueberries, and cherries led to an increase in the erosion of surface hardness on the tooth samples.
Another possible side effect of drinking smoothies is the formation of oxalate crystals in your body
which can lead to kidney problems. Oxalic acid is a compound found in many different foods, but is especially high in certain leafy green vegetables like spinach.
Certain leafy greens that are popular choices for smoothies, like kale or spinach, are often high in vitamin K.
For people who have an issue with too many blood clots or need to take blood thinners for other reasons, too much vitamin K can be an issue.
Studies have shown that cruciferous vegetables (think kale, broccoli, cabbage, etc.) can actually block
the production of thyroid hormones with a natural compound called glucosinolate. These are known to lower the intake of iodine in the thyroid and therefore potentially lead to thyroid disorders.
Before you go stuffing your blender to the brim with kale, you may want to read about a toxic metal found in soil called thallium.
This heavy metal is commonly found in soil.Thallium prefers to latch on to growing cruciferous veggies like broccoli, cauliflower, bok choy, and most importantly for green smoothie lovers: kale.