Is your green smoothie doing more harm than good?

Yes, green smoothies are having a moment, and have been seized up by all factions of the fitness and dieting world—from vegans to Paleo aficionados—as a healthful and delicious addition to any diet. But, while these wonderfully colorful and healthy drinks can be really good for you, they may have a dark side as well. [Cue: Darth Vader breathing.]

The typical green smoothie is full of vegetables, maybe a little fruit, maybe some milk (almond, regular, or coconut), protein powder, and yogurt. Ingredient choices are almost limitless, and personal preferences strong. And, many people are almost religious in their approach to smoothies—as a meal replacement or snack—and drink them daily. But, as it always turns out, too much of a good thing can be bad.

Thallium. Smoothies are usually chock full of the cruciferous vegetables—we’re talking kale, broccoli, cauliflower, and cabbage—and other leafy greens. Unfortunately, cruciferous vegetables have been found to contain high levels of thallium, a toxic heavy metal.  

Thallium is found in the soil, and is a byproduct of smelting and coal-burning. It has a tendency to preferentially accumulate in cruciferous vegetables, including Brussels sprouts, kale, broccoli, cauliflower, cabbage, and bok choy.

So, that daily green smoothie may be exposing you to high levels of thallium. Now, even low exposure to thallium can cause symptoms such as diarrhea, stomach pain, nausea, hair loss, and peripheral neuropathy. Just imagine what high levels of the stuff could do.

And because heavy metals can accumulate in your body over your lifetime, your daily green smoothie habit could become a big problem over time.

One solution is to use only organic cruciferous vegetables to whip up your smoothies. Here’s why: Unlike the soil on many conventional farms—which has typically been carbon-depleted—the soil found on organic farms is usually rich in carbon-based matter. This is important because carbon-based matter can actually slow or stop the transfer of thallium into plants.

So, carbon basically cancels thallium. You can see where this is going, can’t you? For a healthier green smoothie, go organic.

Goitrogens. In addition to thallium, cruciferous veggies also contain goitrogens. This is not good because goitrogens—specifically glucosinolates—are naturally occurring plant chemicals that have the ability to inhibit iodine uptake by the thyroid and reduce thyroid hormone production. This could be particularly bad for people with iodine deficiency and thyroid disorders.

But, there’s a fix for this, too—though you may not like it. Cooking cruciferous veggies helps deactivate the glucosinolates.

Oxalates. And the leafy greens rounding out your smoothie are not innocent bystanders either. Though leafy greens are generally nutritious, the downside is that, when consumed in large amounts, they could fill you with oxalates, another plant-based compound.

Oxalates occur in high amounts in spinach, collard greens, chard, dandelion greens, broccoli, cabbage, carrots, beets, and berries, and they can actually promote the formation of kidney stones and inflammation.

In some, oxalate accumulation can cause inflammation, and has been found to be associated with chronic pain, fibromyalgia pain, vulvar pain, and neurological symptoms.

Considering that a cup of raw spinach can contain approximately 656 mg of oxalate, and high oxalate intake is defined as consuming 250 mg/d, it’s easy to see an oxalate overdose happening after drinking daily green smoothies. How many cups of spinach do you use for your smoothies? Chances are, it is more than 1 cup.

So, how can you combat the unhealthy effects of oxalates? Restocking your gut with beneficial bacteria from fermented foods and probiotics can help your body degrade oxalate. Several probiotic species—Lactobacillus rhamnosus, Bifidobacterium animalis subspecies lactis BI07, and Oxalobacter formigenes—have been shown to be especially helpful oxalate “degraders.”

In addition, it may help to rotate out the ingredients in your beloved green smoothies to include leafy greens that are naturally low in oxalates—ie, mustard greens, watercress, and lettuce.

So, when you’re whipping up that delicious green smoothie for breakfast, lunch, or your midday or post-workout snack, remember thallium, goitrogen, and oxalate content. As with everything in your diet, it is always safer to err on the side of moderation. Overdoing anything—including green smoothies—is never a good idea.