Cancer-preventative powers of superfood kale
Kale is a nutrient-dense “superfood” that has a tremendous range of health benefits that exceeds its individual nutrient properties. It is classified along with collards, Brussel sprouts, cabbage and other vegetables within the Brassica family. The Brassica vegetables are rich in phytonutrients containing sulfur and powerful antioxidants.
Of all the super-food nutrients found in kale, methyl cysteine sulfoxides and glucosinolates are two of the most critical types of compounds in supporting health. These nutrients assist in activating detoxifying liver enzymes that are responsible for neutralizing carcinogenic substances. Sulforaphane is one type of glucosinolate that is released during the process of chewing and digesting kale or through the chopping of the vegetable. Sulforaphane is a potent antioxidant which has been found to boost the detoxification activity of liver enzymes by altering genetic expression. (1, 2, 3])
Kale is dense in cancer-preventative nutrients
Isothiocyanates are a type of glucosinolates. These nutrients have been shown to stimulate apoptosis (cellular death) in cancer cells and prevent cancer formation. (4, 5]) When kale is damaged via chopping or chewing, the enzyme myrosinase helps release isothiocyanates by interacting with glucosinolates.
David Jockers DNM, DC, MS is a doctor of natural medicine, functional nutritionist, and corrective care chiropractor. He owns and operates Exodus Health Center in Kennesaw, Georgia.
This process increases the bioavailability of nutrients to be absorbed by the body. You would be right to assume that this means raw kale contains more isothiocyanates capable of absorption by the body than cooked kale. Boiling this “super food” for 9 to 15 minutes shows a dramatic decrease in the total glucosinolate content to anywhere from 18 to 59 percent. (6]) Other cooking mechanisms, such as steaming or sautéing, also contributes to a reduction in nutrient density.
Kale ranks first in class in its antioxidant content compared to other vegetables. It is high in the antioxidants lutein, zeaxanthin, and carotenoids like beta-carotene. It is the hue of these nutrients that provides kale with a natural defense against solar radiation damage.
In fact, these antioxidants are so powerful at contributing to health, that the USDA has spent more than $800,000 into a four-year “Carotenoid Project.” In combined efforts, plant biologist Dr. Dean Kopsell and nutritional scientist Dr. Joanne Curran-Celentano are analyzing the effects of carotenoids and their contribution to their natural health phenomena.
Kale has UV radiation protection
Dr. Kopsell supports the evolutionary belief that plants developed carotenoids over time in order to protect against overexposure to UV radiation. “Plants use only about one or two percent of the light energy falling on the leaf surface for photosynthesis” according to Kopsell. He also states that “in plants, lutein and zeaxanthin play a role in absorbing light outside the red and blue range and funneling it away, in essence acting as a chemical ‘sun block’ that helps protect the plant from excessive radiation.” (7])
Researchers also speculate that carotenoids perform similar duties by concentrating in the region of the human eye responsible for the highest visual activity known as the macula lutea.
As part of the Carotenoid Project, Dr. Curran-Celentano gathered information concerning 23 different varieties of kale. She analyzed the environmental, genetic and geographical factors that influence the concentration of xanthophyll carotenoids zeaxanthin and lutein. As part of the research, the nitrogen and sulfur content of the soil was altered resulting in a unique antioxidant complex and a stronger flavor in kale that not all people prefer. Kale varieties containing the highest amount of carotenoids had two and a half times the amount compared to kale with lower concentrations. (8])
This finding supports that soil condition greatly influences the nutritional value of kale. Soil health is different depending on the practices used by farmers regarding fertilization, composting and rotational schedules. Studies find that organic-grown kale varieties are worth the extra splurge in cost for their richer nutrient density than conventionally farmed kale. It is best recommended to consume kale from organically grown local farms and gardens.
Kale provides chemo protection
The resulting superfood powers of kale make it an excellent food source to combat the carcinogenesis of multiple cancer types. Its essential nutrients to human health complement one another and provide several anti-cancer benefits.
The compound sulforaphane is largely responsible for the chemopreventive effects of kale. Sulforaphane protects cells by binding to genes that induce antioxidant pathways in the body. This nutrient is critical for repairing tissue susceptible to oxidative damage such as the intestines. The lower digestive tract is constantly fighting to repair itself from environmental toxins we take in every day.
Inflammation in the intestines produces damaging reactive oxygen species (ROS) which initiate DNA damage, reduces oxygen flow to tissue and results in the further generation of pro-inflammatory cytokines and injury. (1) Sulforaphane increases the expression of detoxification enzymes and genes that code for antioxidants. These enzymes and antioxidant systems scavenge ROS and slow the carcinogenesis of colon cancer. (4])
The liver is the closest organ to the intestines and readily influenced by any injury to intestinal tissue. Detoxifying the intestines of free radicals like ROS thus inhibit the pathogenesis of disease in the liver. Clinical studies have shown that the presence of ROS in the intestines generates an inflammatory response in the liver characteristic of circulating leukocytes. (1])
Nutrients in kale support other antioxidant defense systems critical for the detoxification of ROS as well. Manganese for example supports superoxide dismutase (SOD) in neutralizing free radicals. Other studies support that the combined antioxidant activity of kale’s phenolic compounds increases the cellular levels of the super antioxidant powerhouse glutathione. SOD, glutathione, and other free radical scavengers stimulated as a result of the nutrient content in kale effectively restrain ROS from damaging liver cells and can combat the development of liver cancer. (9])
Long-term epidemiological studies have suggested that a diet high in sulfur-containing veggies, like kale, can significantly reduce the risk of bladder cancer. The conversion of glucosinolates into isothiocyanates in kale is shown to possess chemoprotective properties. Researchers have found that isothiocyanates may be responsible for both the prevention of bladder cancer and the ability to suppress its recurrence or progression.
- Detoxify carcinogens
- Inhibit DNA damage
- Induce apoptosis in cancer cells
- Improve the modulation of the cell cycle
- Reduce cancer causing enzymatic pathways
Decades of studies analyzing diets high in vegetable consumption support the effects that nutrients contained in veggies reduce human cancers. Particularly, epithelial cancers of the respiratory tract are closely associated with this reduced cancer risk. Researchers propose that a combination of carotenoids, vitamins, fiber, and phytochemicals have a synergistic effect on inhibiting cancers pertaining to the respiratory system in the following ways: (12])
- Increase detoxification enzymes
- Inhibit potent carcinogens involved in tumor growth such as nitrosamines
- Provide materials needed in cancer-fighting agents
- Regulate hormone pathways
- Bind and dilute carcinogens along the digestive tract
- Exhibit antioxidant properties
Poor nutrition intake coupled with polluted environmental conditions increases the risk for respiratory cancers such as lung, tracheal and laryngeal tumors. (11]) Adding kale to your diet will not only help you reduce your risk of cancers related to the digestive tract, but the super-food nutrients it contains will promote overall health and total wellbeing.
Typically, a major transcription factor involved in the expression of detoxification genes known as Nrf2 remains in a dormant state in the body. Dietary phytochemicals release Nrf2 so that it can stimulate detoxification genes and enzymes to remove carcinogens. (13]) The phytonutrients in kale promote the expression of Nrf2 and halt the progression of cancer cells. Specifically, sulforaphane activates Nrf2, which is significantly impacted by oxidative stress associated with oral cancer.
Oral cancer affects tissues in the mouth and can also invade the sinuses and throat. Sulforaphane has been used in treating oral cancer cells taken from humans by upregulating the Nrf2 pathway and reducing signs of oxidative stress and damage. However, researchers found that sulforaphane alone was not responsible for this treatment effect. The phytonutrient complex of isothiocyanates had to be present with sulforaphane in order to exhibit cancer preventative properties. Kale contains both sulforaphane and isothiocyanates. (14])
Ways to consume kale
As you can see, kale is loaded with cancer-fighting antioxidant compounds and should be a staple in a cancer prevention or a cancer healing protocol. Steamed kale and baked kale chips are more tasty ways to consume kale but have significantly lower isothiocyanates. They are still enjoyable ways to get kale into your body, but won’t pack the same cancer-prevention punch as raw kale.
Chewing raw kale is very tough on the digestive tract. I recommend juicing kale or blending it into smoothies. You also can make a kale salad dressing by taking kale, olive oil, lemon or lime, apple cider vinegar, and herbs and blending them together until the kale is fully broken down.
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- Myzak MC, Dashwood RH. Chemoprotection by sulforaphane: keep one eye beyond Keap1. Cancer Lett. 2006 Feb 28;233(2):208-18. Review. PMID: 16520150
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- Yang Y, Yan H, Li Y, Yang ST, Zhang X. Isothiocyanates from Broccolini seeds induce apoptosis in human colon cancer cells: proteomic and bioinformatic analyses. Pharmazie. 2011 May;66(5):382-90. PMID: 21699074
- Abbaoui B, Riedl KM, Ralston RA, Thomas-Ahner JM, Schwartz SJ, Clinton SK, Mortazavi A. Inhibition of bladder cancer by broccoli isothiocyanates sulforaphane and erucin: characterization, metabolism, and interconversion. Mol Nutr Food Res. 2012 Nov;56(11):1675-87 PMID: 23038615
- McNaughton SA, Marks GC. Development of a food composition database for the estimation of dietary intakes of glucosinolates, the biologically active constituents of cruciferous vegetables. Br J Nutr. 2003;90(3):687-697. PMID: 13129476
- Kopsell, et al. The Effects of Ultraviolet Radiation on Pigment Production, Growth, and Photochemical Efficiency in Allium spp. Masters Thesis at University of Tennessee. April 2009. Source
- Kopsell, et al. Genetic and environmental influences on the nutritional content of vegetable brassicas. United States Department of Agriculture. Oct 2001- Sept 30th. Source
- Fernandes Fatima, et al. Kale Extract Increases Glutathione Levels in V79 Cells, but Does not Protect Them against Acute Toxicity Induced by Hydrogen Peroxide. Molecules 2012. 17(5): 5269-5288. DOI: 3390/molecules17055269
- Fahey JW, Zhang Y, and Talalay P. Broccoli sprouts: An exceptionally rich source of inducers of enzymes that protect against chemical carcinogens. Proc Natl Acad Sci USA. 1997 Sep; 94(19): 10367-10372. PMCID: 23369
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- Gopalakrishnan A, Kong TAN. Anticarcinogenesis by dietary phytochemicals: cytoprotection by Nrf2 in normal cells and cytotoxicity by modulation of transcription factors NF-kappa B and AP-1 in abnormal cancer cells. Food Chem Toxicol. 2008 Apr; 46(4): 1257-70. PMID: 17950513
- Lan A, et al. Chemoprevention of oxidative stress-associated oral carcinogenesis by sulforaphane depends on NRF2 and the isothiocyanate moiety. 2016 Jul. DOI: 18632/oncotarget.10609