The first thing you learn in a toxicology course is that too much of a good thing is harmful. Even water can be toxic if you drink too much of it. And this concept is also true for microgreens.
Microgreens are safe to eat within the reccommended daily amount of vegetables, which is approximately 5 servings of vegetables or 375g. However, if you are suffering from thyroid or calcium deficiencies, then you should consult your doctor or dietician because there are vegetables that would affect your condition.
Another aspect of safety that you should be aware of is the microbial safety of your microgreens. Because microgreens are grown and packaged in high densities, growers that are unaware of practices that reduce the spread of contamination are risking the wellbeing of their consumers.
First, let’s examine the case of a woman who was hospitalized from eating too much bok choy. Bok choy is a vegetable in the brassica family (closely related to kale and broccoli) which contains the highest amount of cancer fighting phytochemicals such as sulphoraphane and glucosinolates. Nutrient wise, it contains plenty of Vitamin A, B, C, K, as well as calcium and iron.
Also known as Chinese Cabbage, it is one of the most popular vegetable grown at home and commercially as microgreens. So the question is how is too much of a good thing bad?
The hospitalized woman was an 88 year old diabetic, eating 1.3 to 1.5 kg (or 2 to 3 pounds) of raw bok choy a daily for several months. The amount she consumed is only three times higher than the daily reccommeded amount of leafy greens. Whether it was insanity or pure willpower, she didn't eat bok choy with any form of seasoning. When the responders rolled her into the hospital, she was diagnosed with high blood pressure, swelling around the eyes and tongue.
Through a live saving blood test, the doctors quickly figured out that her thyroxin levels (thyroid hormones) were undetectable. Her thyroid gland shrank significantly. The cause for her disorder is a family of antioxidants called glucosinolates, which are enriched in bok choy, as well as kale and broccoli.
Because glucosinolates are antioxidants, they prevent cancer by reducing DNA damage. On the other hand, glucosinolates enzymatic byproducts inhibits the uptake of iodine by the thyroid gland.
The lack of iodine causes the thyroid gland to shrink. The whole issue would be averted if she were to cook the vegetable. Cooking the vegetables would deactivate (denature) the enzyme (myrosinase), keeping the anti-cancer properties while reducing the toxic byproducts.
Since microgreens have higher levels of phytochemicals, should you be worried?
The brassica family of vegetables was widely known in the literature to inhibit thyroid function and iodine uptake due to compounds called goitrogens. And this affects people diagnosed with hypothyroidism severely.
The brassica family of vegetables includes broccoli, kale, turnip, arugula and bok choy. These vegetables offer different levels of phytochemicals and myrosinase: Broccoli and arugula are known to have the highest levels of myrosinase, while bok choy has the highest levels of phytochemicals. Myrosinase hyrolyze (convert) beneficial phyrochemicals into toxic byproducts. Fortunately, this enzyme can be deactivated by heat, which is the method used in the study to isolate phytochemicals in microgreens. And this same study showed that these phytochemicals reduce the incidence of breast cancer in rats.
Iodine levels are important for the prevention of gout, and is one of the critical minerals to monitor for your health.
Should you be concerned about microgreens? Broccoli microgreens and sprouts have been known to have 10 times higher levels of glucosinolates and isothiocyanates. And if they were to be hydrolzed by myrosinase, then you have a thyroid issue.
Therefore, in order to maximize the cancer fighting effect of brassica microgreens and decrease its thyroid inhibitor toxicity, cooking brassica microgreens is highly recommended. I'm not one to reccommend how people should eat vegetables, but some researchers suggests that chewing vegetables releases more myrosinase. So should you eat it raw, the reccommendation is to not chew your vegetables.
Plants in the wild are surrounded by fierce competition, where they have to sequester as many nutrients as possible from their environment. Plants use chemical chelators such as oxalates to bind minerals such as iron and calcium from leeching into the soil. Oxalates are found in a variety of vegetables such as spinach, amaranth, parsley, beets and buckwheat. All of these vegetables are commonly grown as microgreens.
Oxalates not only bind the minerals in your diet, but also your urine. They are progenitors of kindney diseases such as kidney stones. So the big question is: since microgreens have a higher concentration of phytochemicals, do microgreens contain a higher concentration of oxalates?
There aren't many studies on oxalic acid content in vegetables because they are very difficult to extract, and there aren't any oxalic acid study with regards to microgreens. However, we can guesstimate the amount of oxalic acid in microgreens with a little bit of detective work.
Oxalic acid is biosynthesized from the incomplete oxidation of carbohydrates.
And plants primarily derive their carbohydrate source from photosynthesis. Since microgreens have less leafy area for photosynthesis, they have less amount of carbohydrates and carbohydrates derivatives, including the amount of oxalic acid. And since microgreens (not sprouts) have exhausted their carbohydrate resource at the time of harvest, they should have similar amount of oxalic acid to mature plants when you normalize them by weight.
So, if you have severe calcium or iron defficiency and are able to eat spinach on a regular basis, then eating the same volume of microgreens will be a non-issue.
Microbial safety is the most life threatening issue out of the three. There are multiple cases of E. coli outbreaks and Salmonella outbreaks in the food industry, causing millions of dollars in damages and product recalls. (4)
Salmonella causes typhoid fever, severe diarrhea and vomiting. While E. Coli causes symptoms such as hemorrhagic diarrhea and severe cramps. You will be hospitalized if you come in contact with these bacteria.
The bad news is that the culture surrounding microgreens consumers and growers are more likely to cause such outbreaks.
First, we really don’t like to cook our foods. While you do get more nutrients and enzymes when you eat your vegetables raw, it doesn't remove bacteria that may have contaminated the vegetable.
Second, we like to grow our vegetables all organic. But wait, isn’t growing organic good? Not in the context of micro farming.
When a farmer are growing normal vegetables outdoors, organic is better. You’re saved from pesticides, herbicides and fungicides chemical cocktails that are harmful to your health and environment. These chemicals aren't regulated the same degree they regulate drugs, which means that small amounts are allowed in the final product, even if they are shown to cause cancer.
Without these chemicals, there would be massive losses of vegetables due to insects, weeds, and fungus, which is why organic vegetables usually cost double.
But when you’re growing commercial microgreens indoors, the farmer uses soil-less growing medium. Soil-less medium doesn’t have weeds, so they won’t need to use herbicides. They also grow the plants indoors in an enclosure, which means they don’t need to spend money on pesticides. Moreover, they grow vegetables in a high light and low humidity environment, which means that they don't need to use fungicides.
But the problem with organic farming is that you have to use organic fertilizers. The two cheapest organic fertilizers are animal manure and blood meal. Organic fertilizers such as animal manure and blood meal are the primary vectors for E. coli and Salmonella contamination.
Synthetic fertilizers are better for growing microgreens than organic fertilizers. Synthetic fertilizers are readily available for plants to use right away, whereas organic fertilizers take at least a couple of months to be effective. Moreover, microgreen growers don't have fertilizer runoff because the farm is self-contained.
For farmers that grow microgreens hydroponically, contamination should be taken seriously. Once the water reservoir is contaminated, the bacteria will spread throughout the entire system, form biofilms and will continue to spread unless the whole system is sterilized. It's not uncommon to hear outbreaks of E.Coli with hydroponically grown lettuce.
There are ways to reduce the risks of bacterial spread. Washing microgreens with a dilute ascorbic acid prior to packaging reduces the amount of microbes significantly. And of course, when dealing with food, all employees must wash their hands before handling microgreens.
I am the author of this website and owner of growyourmicrogreens.com. I am an hobbyist gardener and a passionate scientist. I was trained as a scientist in the Molecular Genetics program in University of Toronto, where I received my Masters of Science and published a journal article.