Green smoothie Nora Kuby - Is Your Obsession With Green Smoothies Ruining Your Metabolism?

Is Your Obsession With Green Smoothies Ruining Your Metabolism?



I know what you’re thinking. ‘How in the hell can something as pristine, wholesome, and planet-saving as a green smoothie possibly be bad for my metabolism?’


Aside from any health-promoting benefits, a green smoothie is the new Starbucks for the privileged health-conscious few. Conveying status, people love to be seen consuming them in public, in a self-righteous manner, whether that’s sipping them whilst strolling along busy city sidewalks or on public transport.

Milk mustaches are so last century.


Let’s face it. Certain foods such as kale, goji berries, and the green stuff like kale, broccoli, Bok choy, Swiss chard, collard greens and other leafy vegetables have been enjoying almost God-like status and with good reason. They are very nutritious foods. In their raw state they have compounds that help support the liver detoxify the body via Phase 1 and Phase 2 pathways [legitimate detoxification versus the hype you hear around ‘cleanses’ and ‘detox’ fasts etc].


But is there any merit to the current fad of consuming glass after glass [or rather mason jar after mason jar for the uber hip], of raw green smoothies without any regard to potential negative effects? Many people consume them on a daily basis and sometimes more than once a day or at the very least several times a week. For many, the more the  better they say…


Proponents of the green-smoothie religion cite effortless benefits such as

  • energy boosting
  • detoxification of poisons stored away in fat cells
  • ‘alkalizing’ the body
  • natural weight loss
  • year-round health
  • disease-fighting antioxidants and phytonutrients and
  • a healthy alternative to fast food


And in many ways they’re right but is it possible to get too much of a good thing?


Legendary Green Smoothies_Nancy White

What are the possible down sides of all that green?

Like with any new ‘diet’ or exercise program, people will initially feel great because a lot of ‘bad’ habits fall by the wayside. People often consume less coffee, sleep better, give up junk food and other highly processed foods. It’s no different with green smoothies; people tend to start eating better overall once adopting these emerald-coloured wonders.




Consuming large quantities of raw crucifer vegetables, which are often the foundation of green smoothies, can have a dark side. As far back as 1929 researchers from John Hopkins University were able to demonstrate a down side to these long-revered vegetables; consumption of large quantities were able to induce goiter in experimental animals.


Iodine metabolism in response to goitrogen induced altered thyroid status under conditions of moderate and high intake of iodine


Goiter is the classic iodine deficiency disease of the thyroid gland characterized by swollen protrusions of the neck since the thyroid gland is found there. In an attempt to capture as much iodine as possible, the thyroid gland grows to increase the surface area of the tissue; in essence ‘casting a wide net’.




But goiter can also be caused by exposure to an excessive amount of goitrogens; compounds found in both the environment and food that inhibit the uptake of iodine by the thyroid gland. At low concentrations the goitrogens in green smoothie must-haves such as raw kale,  raw spinach, raw Bok choy, raw Swiss chard, raw broccoli & broccoli sprouts and so on, can impeded the thyroid from getting optimal amounts of iodine from food. Typically this isn’t a big deal if the diet contains sufficient amounts of iodine but iodine is a lot more scarce than it used to be.


Effects of radish on thyroid status under conditions of varying iodine intake in rats


How high can you go?

The real concern is that consuming large amounts of highly concentrated goitrogens [a.k.a. green smoothies] can inhibit the thyroid from absorbing any iodine that might be in the blood [serurm]. Worse still, at very high levels, goitrogens have the potential to block the action of any iodine that does get into the thyroid and consuming more iodine can’t over come the antagonistic properties of these blenderized crucifer concoctions.


The unanswered question centers on the impact of chronically consuming higher than usual amounts of goitrogens on iodine metabolism and thyroid health over the long term. Green smoothies are relatively new on the timelines of human nutrition and guzzling them down is uncharted territory.  It is for this reason that anyone with thyroid health issues are advised to avoid/minimize foods rich in goitrogens in the first place.


Should the health conscious simply turn a blind eye?


On a side note, green smoothies may also be bad news for nursing mothers as goitrogens can inhibit the transfer of maternal dietary iodine into breast milk. Iodine is absolutely critical for developing fetuses. Without iodine, a form of mental retardation can occur called cretinism resulting in impaired growth and mental development. This is why maternal multivitamins provide an ample amount of iodine.


Nutritional epidemiology and thyroid hormone metabolism

But what about metabolism?

A lot of us struggle to get enough iodine for optimal health for two main reasons: 1) the iodine content of the food supply has been decreasing over the past 60 years and 2) the anti-sodium frenzy has resulted in many ditching the salt shaker. Iodine was added to table salt in the early part of the 20th century to prevent, you guessed it, goiter. But many have given up using table salt because they are worried about getting too much sodium and therefore are missing out on a vital source of iodine. For the record, the pinch isn’t the problem. Small amounts added to cooking or at the table doesn’t count for much of our sodium intake and the salt that is used for food production doesn’t use iodized salt.


Iodine is vital for a healthy thyroid, the master of metabolism. Without it, we won’t make adequate amounts of thyroid hormones and our cellular energy output grinds to a halt. Making matters worse is the potential for dietary goitrogens that, if eaten in large enough amounts, could aggravate a diet already low in iodine.


Couple this with other ‘healthy’ behaviours such as drinking 8 to 10 glasses of water per day, a diet based on eating high-fiber, high-water foods that are low in starch, restrictive dieting (I mean ‘clean eating’), a lack of adequate sleep and excessive exercise, stress and burning the candle at both ends and you have a recipe for disaster; metabolic rate can drop with long term negative consequences.


Daily/weekly consumption of low-calorie, green vegetable smoothies with loads of raw crucifer vegetables can tip the balance for someone with a lowish metabolism towards a metabolism that’s in his or her boots. The results? Cold hands and feet, frequent trips to the washrooms with clear watery pee, crashing moods and energy levels and no sex drive.


Sound familiar?



What to do?

None of this is to suggest that you can’t enjoy the occasional green smoothie in small amounts if you truly enjoy them, but rest assured, they are not needed for optimal health. You can get all of their health promoting properties from small amounts of raw whole vegeables as opposed to the very large amounts in a concentrated shake. Some raw kale mixed into salad, broccoli and dip, coleslaw etc are reasonable ways to reap their benefits but it’s too easy to over-consumed them and their goitrogenic compounds when they’re in a beverage format.


Regardless, to counter any metabolism-crashing impact that the green devil may have caused, be sure to enjoy a variety of both cooked and raw vegetables, include some iodized sea or table salt everyday, choose a good quality multivitamin with minerals that includes iodine, include more calorie-dense foods like potatoes, pasta, rice, dried fruit, honey & syrup, saturated fats like Brie, cream, coconut oil and yes, even some sugar and ease up on the water [for more see here, and here] and get adequate sleep. If any of the symptoms of a low metabolism don’t improve, you may need to meet with a qualified nutrition professional to asses your diet for a little metabolism rescue and repair.


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