IngredientsCollard is a group of loose-leafed cultivars of Brassica oleracea (the same species as many common vegetables, including cabbage and broccoli), part of the Acephala Group and also classified as the variety B. oleracea var. viridis. The name "Acephala" refers to a group of leafy cabbages "without head." Collard bears the same botanical name as kale, from which it differs only in leaf characters: collard leaves are much broader, are not frilled, and resemble those of head cabbage.
"Collard" is the shortened American word for colewort (or cole), which means "cabbage plant." Collard greens are known variously as couve (Brazil), couve-galega (Portugal), kovi or kobi (Spanish-speaking countries), haak (Kashmir), and sukuma wiki (East Africa).
Collard greens belong to the Brassicaceae family, also known as the cruciferous vegetable family. This group includes many nutritionally important vegetables, such as cabbage, broccoli, kale, and Brussels sprouts, all derived from the species Brassica oleracea through selective breeding.
The main stem reaches a height of 60–120 cm (24–48 inches) with a rosette of leaves at the top. Lower leaves are commonly harvested progressively; the entire young rosette is sometimes harvested. The vegetables of the Acephala group of Brassica oleracea are biennial cultivars and originated in the Mediterranean region but have gained popularity worldwide due to their strong tolerance toward unfavorable environmental conditions, as well as their nutritional aspects and versatility in recipes.
Popular cultivars of green collard include "Georgia Southern," "Morris Heading," and "Couve-Manteiga." The vegetable is primarily grown by commercial farmers in the Southern United States—with South Carolina and Georgia as leading producers—as well as by home gardeners and small-scale farmers, particularly in the Southeast. They are also widely cultivated in East Africa, Brazil, and parts of Europe.
Collard greens are consumed and prepared in several forms:
Collard has been cultivated as food since classical antiquity. Originating in the eastern Mediterranean region, collard greens have been cultivated for thousands of years, with evidence suggesting their consumption dates back to ancient Greece and Rome. Collards have been cultivated in Europe for thousands of years, with references to the Greeks and Romans back to the 1st century CE.
In Montenegro, Dalmatia, and Herzegovina, collard greens, locally known as raštika or raštan, were traditionally one of the staple vegetables. They are particularly popular in the winter, stewed with smoked mutton (kaštradina) or cured pork, root vegetables, and potatoes. Known in Turkey as kara lahana ("dark cabbage"), it is a staple in the Black Sea area. It is also an essential ingredient in many Spanish soups and stews, like the pote asturiano, from the Asturian province. In Portugal and Brazil, a type of collard green known as couve is a staple ingredient in dishes like caldo verde, a traditional soup.
West Africans used collards and other leafy greens to make stews. Enslaved people in the United States used collards to supplement their diets and used what they had on hand to survive. During the time of slavery in the U.S., collards were one of the most common plants grown in kitchen gardens and were used to supplement the rations provided by plantation owners.
Collard greens are a staple vegetable in Southern U.S. cuisine. They are often prepared with other similar green leaf vegetables, such as spinach, kale, turnip greens, and mustard greens in the dish called "mixed greens." Typically used in combination with collard greens are smoked and salted meats such as ham hocks, smoked turkey drumsticks, smoked turkey necks, pork neckbones, and fatback. Traditionally, collards are eaten on New Year's Day, along with black-eyed peas or field peas and cornbread, to ensure wealth in the coming year. Cornbread is used to soak up the "pot liquor," a nutrient-rich collard broth.
Collard greens are part of the South's culinary traditions, especially in Black households. The plant's centrality to African-American foodways reflects the broader history of the Great Migration and cultural continuity, and the vegetable is now the subject of heirloom seed conservation efforts.
Collards may have arrived in southern Morocco via early Muslim traders, and Morocco may have been a stop in the journey the vegetables took to America. Research has begun to trace possible historical routes from the Middle East through North Africa to the Americas through rare historical documentation.
Raw collard greens are 90% water, 6% carbohydrates, 3% protein, and contain negligible fat. Collard greens' profile of being low in calories and high in fiber, protein, and minerals such as calcium and potassium support their suitability as a functional food.
Like kale, collard greens contain substantial amounts of vitamin K (339% of the Daily Value, DV) in a 100-gram (3.5 oz) serving. Collard greens are especially rich in calcium and vitamin K, both of which are important for bone health. Just 1 cup (170 grams) of cooked greens provides 27% of the DV for calcium and an impressive 883% of the DV for vitamin K.
Collard greens are an excellent source of vitamin K, vitamin A (in the form of carotenoids), manganese, vitamin C, dietary fiber, and calcium. In addition, collard greens are a very good source of vitamin B1, vitamin B6, and iron. They are also a good source of vitamin E, copper, protein, magnesium, phosphorus, vitamin B5, folate, omega-3 fatty acids, niacin, and potassium.
Glucosinolates (S-glucopyranosyl thiohydroximates) are naturally occurring S-linked glucosides found mainly in cruciferous vegetables. They are enzymatically hydrolyzed by myrosinase to produce sulfate ions, d-glucose, and characteristic degradation products such as isothiocyanates (sulforaphane, erucin, etc.), thiocyanate, epithionitrile, nitrile, and goitrin. Isothiocyanates are believed to be responsible for the physiological activity of these plants.
Phytonutrients in collard greens include phenols like caffeic and ferulic acid, flavonoids like quercetin and kaempferol, and glucosinolates like glucobrassicin and glucoraphanin. Collard greens are a particularly rich source of a glucosinolate called glucoraphanin, which can be converted into sulforaphane, and glucobrassicin, which is a precursor to indole-3-carbinol.
Sulforaphane (SFN, molecular formula C₆H₁₁NOS₂) is the biologically active isothiocyanate produced by the metabolism of glucoraphanin by the enzyme myrosinase. Myrosinase is present in plant cells and is compartmentalized separately from the glucosinolates. Sulforaphane was also found in Brassica oleracea species including Brussels sprouts, white cabbage, kohlrabi, cauliflower, collard greens, and savoy.
The indole I3C (indole-3-carbinol), which upon exposure to gastric acid undergoes self-condensation to form DIM (3,3'-diindolylmethane), is also present in cruciferous vegetables, including broccoli, cabbage, cauliflower, Brussels sprouts, collard greens, and kale, and is used as a chemopreventive agent.
Collard greens are a best source (>50% daily value) of carotenoids, glucosinolates, and vitamin K; an excellent source (20–50% daily value) of manganese, polyphenols, vitamin A, vitamin C, and vitamin B9 (folate); and a good source (10–20% daily value) of calcium, dietary fiber, and vitamin E.
Chlorophyll, an essential bioactive compound found in satisfactory amounts in collard greens, is associated with reducing oxidative stress, preventing DNA damage, and offering potential antitumor benefits. The leaves of collard greens have been analyzed for proximate composition, mineral content, amino acid and fatty acid profiles, and chlorophyll levels; chlorophyll retention was measured after sous vide cooking and freeze-drying to assess the efficacy of these preservation methods.
Collard greens contain a number of healthy phytonutrients and antioxidants, specifically carotenoids beta-carotene, alpha-carotene, and lutein + zeaxanthin, and flavonoids kaempferol and quercetin.
Collards are also a rich source of polyphenols, with 178.6 mg per 2-cup serving. Polyphenols play a role in protecting against cancer, heart disease, diabetes, asthma, osteoporosis, neurodegenerative diseases, and other conditions associated with oxidative stress.
Collard greens are an excellent source of vitamin B9 (folate), providing 23% of the daily value per 2-cup serving. Vitamin B9 is an essential B vitamin that plays roles in blood cell production, the formation of genetic material (including DNA), and cell growth and function. It is particularly important during pregnancy, when folate demands increase due to the rapid creation of new cells and DNA. Along with helping protect against fetal development problems, folate can support cardiovascular health, potentially protect against certain cancers, and reduce the risk of cognitive and neurological disorders later in life.
Sulforaphane is the most potent naturally occurring inducer of the Keap1-Nrf2 pathway, which is best-known for its upregulation of antioxidant and detoxification mechanisms as well as its anti-inflammatory potency. The major mechanism by which sulforaphane protects cells was initially thought to be through Nrf2-mediated induction of phase 2 detoxification enzymes that elevate cell defense against oxidative damage and promote the removal of carcinogens.
The isothiocyanates (ITCs) made from glucosinolates in collard greens (and other cruciferous vegetables) have been shown to modify enzyme activity in Phase 2 of detoxification and increase the likelihood of detox success.
When collard greens are consumed, fiber-related nutrients in this cruciferous vegetable bind together with some of the bile acids in the intestine in such a way that they pass out of the body in a bowel movement rather than being absorbed along with the fat they have emulsified. When this happens, the liver needs to replace the lost bile acids by drawing upon the existing supply of cholesterol, and as a result, cholesterol levels drop.
Researchers found that steam cooking significantly improved the in vitro bile acid binding of collard greens, kale, mustard greens, broccoli, and cabbage, and concluded that green leafy vegetables, when consumed regularly after steam cooking, would lower the risk of CVD.
Researchers have determined that the sulforaphane made from a glucosinolate in collard greens (glucoraphanin) helps protect the health of the stomach lining by preventing bacterial overgrowth of Helicobacter pylori in the stomach or too much clinging by this bacterium to the stomach wall.
Vitamin K is actually a group of fat-soluble vitamins with a similar molecular structure. This nutrient plays a vital role in coagulation, serving as a cofactor for proteins needed for blood clotting; it is also essential for bone metabolism, cellular function, and the prevention of soft tissue calcification.
Eight studies met the inclusion criteria of a published meta-analysis investigating the relationship between the incidence of total cardiovascular disease and the intake of green leafy vegetables. The overall effect size (random effect model) was RR = 0.842 (95% CI = 0.753 to 0.941), p = 0.002, which indicates a significant 15.8% reduced incidence of cardiovascular disease.
Some studies note an inverse relationship between consumption of cruciferous vegetables (Cruciferae or Brassicaceae) and risk of CVDs. However, these epidemiological findings encompass cruciferous vegetables broadly and are not specific to collard greens alone.
An in vitro study published in the Food Chemistry journal investigated the bile acid binding capacity of eight steamed vegetables. In this study, lab samples were obtained from eight steamed vegetables — collard greens, kale, mustard greens, broccoli, Brussels sprouts, spinach, green bell pepper, and cabbage — and the researchers measured the ability of all eight vegetable samples to bind bile acids, and the winner of this measurement process was collard greens. This is an in vitro finding and does not directly translate to confirmed clinical outcomes in humans specific to collard greens.
Studies show that individuals who increase their intake of dietary vitamin K have a lower risk of cardiovascular mortality. Getting enough vitamin K2 can help protect against cardiovascular disease, may improve bone mineral density and skeletal health, and may even support endocrine function and brain health; there is also some limited evidence it has anti-cancer and anti-inflammatory properties.
Evidence strength: Epidemiological (meta-analysis level) for green leafy and cruciferous vegetables broadly; in vitro for collard-specific bile acid binding. Direct human clinical trials specific to collard greens and CVD outcomes are not yet available in the published literature.
As a cruciferous vegetable, collard greens contain glucosinolates, substances that the body can convert into various cancer-fighting compounds. Research has shown that eating cruciferous vegetables may help reduce the risk of certain types of cancers, including bladder, colorectal, lung, and prostate.
Several epidemiological and pharmacological studies have demonstrated that dietary glucosinolates and their breakdown products, isothiocyanates, may reduce the risk of carcinogenesis and particular human diseases. International research shows that consumption of cruciferous vegetables decreases the risk of lung, breast, colon, and prostate cancers.
The capacity of isothiocyanates (ITC) such as sulforaphane to be of clinical utility in preventing and treating chronic disease is clear. The health-promoting, preventive, protective, and therapeutic applications of sulforaphane are well established, having been the subject of thousands of studies including more than 125 clinical trials. However, the vast majority of this clinical research uses standardized sulforaphane or broccoli sprout extracts rather than collard greens specifically.
Human studies and studies on collard greens alone are limited. Further research is warranted to better understand how this vegetable may help prevent cancer.
Evidence strength: Moderate-to-strong epidemiological evidence for cruciferous vegetables as a class; preclinical (cell/animal) and clinical evidence for sulforaphane (predominantly from broccoli/broccoli sprout studies). Collard-specific human clinical trials on cancer endpoints are lacking. Claims should not be extrapolated directly from sulforaphane studies to collard consumption without reservation.
Human intervention studies demonstrate that vitamin K not only increases bone mineral density in osteoporotic people, but reduces fracture rates, too. Many older and newer observational studies speculate that a low intake of vitamin K may be linked to an increased risk of bone fractures.
Almost all of the body's calcium is stored in the bones and teeth, where it supports their structure and function. If calcium intake is insufficient for long periods, bones may start to break down, making them thinner and more vulnerable to fractures. Getting enough calcium is particularly important for older adults, especially postmenopausal women.
Calcium content in collard greens aids in maintaining strong bones and teeth, providing approximately 27% of daily calcium needs per cooked cup.
Evidence strength: Strong evidence for dietary vitamin K and calcium in bone health from intervention studies, though these are not specific to collard greens as an isolated food. Benefits for bone health are inferred from the substantial vitamin K and calcium content of collard greens, set against a well-established nutrient-outcome literature.
The role of lutein and zeaxanthin in human health, in particular the health of the eye, is well established from epidemiological, clinical, and interventional studies. They constitute the main pigments found in the yellow spot of the human retina, which protect the macula from damage by blue light, improve visual acuity, and scavenge harmful reactive oxygen species. They have also been linked with reduced risk of age-related macular degeneration (AMD) and cataracts.
Lutein/zeaxanthin was associated with a reduction in the risk of progression to late AMD when compared with beta carotene. These findings from the AREDS2 cohort suggest that the AREDS2 supplement with lutein/zeaxanthin instead of beta carotene was safe, with no association with developing lung cancer and a potential beneficial association with further reduction in progression to late AMD.
However, despite strong biological plausibility, evidence from epidemiologic studies and clinical trials on the relations between intakes of lutein and zeaxanthin and age-related macular degeneration (AMD) has been inconsistent.
Regarding glaucoma specifically, multiple studies indicate that ≥1 serving/month of collards or kale was associated with a 69% lower glaucoma risk. In one review, higher dietary nitrate from leafy greens is consistently associated with lower primary open-angle glaucoma risk, aligning with nitric-oxide-mediated endothelial support and more stable ocular perfusion pressure. Flavonoids (anthocyanins and flavanols), carotenoids (lutein/zeaxanthin), and B vitamins have strong biological rationale for glaucoma prevention but have limited support from long-term, large population-based studies.
Evidence strength: Moderate for lutein/zeaxanthin and AMD (supported by the large AREDS2 trial and prospective cohort data, though results are not fully consistent). Preliminary to moderate for glaucoma risk reduction; the specific collard-frequency association is from observational, not interventional, data.
One cup of cooked collard greens contains about 5.5 grams of fiber — about 20% of the daily value. Fiber is essential for maintaining a healthy digestive system, and diets higher in fiber have also been linked to lower cholesterol levels and reduced risk of colorectal cancer, type 2 diabetes, and obesity.
Dietary fiber is important for helping maintain digestive health. The soluble fiber in collard greens can help absorb cholesterol before it makes its way into the bloodstream, lowering cholesterol levels. The insoluble fiber in collard greens feeds the good bacteria in the gut, which can help with more efficient digestion.
Evidence strength: Dietary fiber's benefits for digestive health are well-supported by a broad body of evidence from clinical and epidemiological studies, though this evidence is for dietary fiber generally rather than from collard greens specifically.
Collard greens provide vitamin A and vitamin C, both of which are important to the immune system. Vitamin C helps keep blood cells healthy and vitamin A is important for healthy T-cells, a part of the immune system that attacks invading bacteria and viruses.
Evidence strength: Well-established roles for vitamins A and C in immune function, though evidence is based on nutrient function rather than on clinical trials isolating collard greens.
No formal therapeutic dose has been established for collard greens as a dietary supplement. Research on cruciferous vegetables typically references serving sizes as consumed in dietary patterns:
Collard greens are available commercially as freeze-dried powder. In this format, the leaves are harvested, frozen, cold-dried, and ground. The high chlorophyll retention rates achieved through sous vide cooking and freeze drying demonstrate the effectiveness of these methods in preserving the nutritional value of chlorophyll. No standardized clinical dosage for collard greens powder has been established in the peer-reviewed literature; commercially, individual scoop sizes are typically calibrated to be equivalent to a set fraction of a cup of fresh leaves (e.g., one scoop equaling one-half cup of fresh collard greens).
This is the most clinically important interaction associated with collard greens consumption. Large changes in the amount of vitamin K in the diet can affect warfarin therapy. This is because warfarin and vitamin K work in opposite ways: vitamin K is a nutrient the body uses to help form natural blood clots, and warfarin prevents blood clots by blocking vitamin K. To keep a steady level of vitamin K in the diet, individuals on warfarin are advised not to change the amounts of vitamin K-rich foods or drinks they consume from day to day or week to week. Vitamin K-rich foods include Brussels sprouts and collard greens.
Importantly, the concern is specifically with inconsistency of intake. Stable, regular consumption is generally manageable through appropriate warfarin dose titration, but sudden increases or reductions in collard consumption can destabilize anticoagulation control.
Raw collard greens contain goitrogens, which can negatively impact thyroid function, particularly in individuals with pre-existing thyroid conditions and low iodine levels. Cooking can deactivate these compounds. Contrary to popular belief, according to the latest studies, foods themselves — collard greens included — are not "goitrogenic" in the sense of causing goiter whenever they are consumed, or even when they are consumed in excess. Most foods that are commonly called "goitrogenic" — such as the cruciferous vegetables (including cabbage, broccoli, kale, and cauliflower) — do not interfere with thyroid function in healthy persons even when they are consumed on a daily basis.
Individuals prone to oxalate kidney stones should be aware that foods such as collard greens, kale, and spinach contain oxalates that can worsen kidney stone formation. Oxalates are water-soluble, meaning that their presence in these foods can be reduced by cooking methods like steaming, boiling, and blanching. Collard greens offer more calcium (268 mg per cooked cup vs. 245 mg in spinach) and fewer oxalates than spinach, which can inhibit calcium absorption.
A sudden increase in fiber intake from collard greens can cause bloating and gas; it is advisable to introduce collard greens gradually to the diet.
Though uncommon, allergies to cruciferous vegetables like collard greens can occur.
Folate is an important vitamin that helps the body grow and is particularly important for small children and pregnant women. Doctors recommend that people who may become pregnant get at least 400 micrograms of folate daily in order to help prevent birth defects like spina bifida. At typical dietary amounts, collard greens are recognized as a healthful source of folate. However, very high supplemental intakes during pregnancy have not been specifically studied for collard greens.
Health conditions that Collard may help support.
Collard greens provide both iron and vitamin C in the same food, a combination that enhances non-heme iron bioavailability — vitamin C converts ferric to ferrous iron, which is absorbed more readily. They also provide folate, deficiency of which causes megaloblastic anemia. These nutritional roles are relevant particularly for plant-based dieters and pregnant women at risk of iron-deficiency anemia.
Collard greens contain multiple classes of antioxidants including vitamin C, vitamin A (beta-carotene), lutein, zeaxanthin, alpha-lipoic acid, and glucosinolate-derived isothiocyanates that activate Nrf2 — the master antioxidant transcription factor. These compounds collectively neutralize free radicals, reduce oxidative stress, and support cellular protection. The National Cancer Institute recognizes cruciferous glucosinolates for their biological antioxidant and chemoprotective activity.
Collard greens contain potassium (~220mg per cooked cup) which counteracts sodium-mediated blood pressure elevation. A study in spontaneously hypertensive rats showed collard green consumption led to a measurable decrease in systolic blood pressure. A broader observational study confirmed that green leafy vegetables including collards can decrease blood pressure and reduce cardiovascular disease risk.
Collard greens have a very low glycemic index (~15) and provide approximately 7–8 grams of fiber per cooked cup, slowing glucose absorption. The fiber content has been linked to reduced inflammation and improved glycemic control in both type 1 and type 2 diabetes in published studies. The antioxidant alpha-lipoic acid in collards may further improve insulin sensitivity.
Collard greens are exceptionally rich in vitamin K (over 880% DV per cooked cup) and provide significant calcium (~27% DV per cooked cup), both of which are critical for bone mineralization. Vitamin K activates osteocalcin and other proteins essential for calcium incorporation into bone matrix. Observational studies link low vitamin K intake to increased fracture risk.
The soluble fiber in collard greens binds bile acids in the digestive tract, preventing their reabsorption and obligating the liver to synthesize new bile from circulating cholesterol, thereby lowering LDL. A study in spontaneously hypertensive rats confirmed reduced LDL cholesterol with collard green consumption. Glucosinolate-derived compounds additionally reduce hepatic cholesterol synthesis.
Collard greens contain glucosinolates that break down into isothiocyanates (e.g., sulforaphane), which activate Nrf2 and inhibit NF-κB — two key regulators of the inflammatory response. A 2021 Frontiers in Pharmacology systematic review confirmed anti-inflammatory effects of cruciferous glucosinolates in both preclinical and clinical studies. Collards also provide vitamin C, beta-carotene, and other antioxidants that reduce oxidative stress-driven inflammation.
Collard greens provide approximately 7.6–8 grams of dietary fiber per cooked cup, combining both soluble and insoluble types. Insoluble fiber adds bulk to stool and accelerates transit, while soluble fiber softens stool consistency. High-fiber diets are well-supported by clinical evidence for preventing and relieving constipation.
Collard greens are a leading dietary source of lutein and zeaxanthin (~14.6mg per cooked cup), carotenoids that concentrate in the macula and retina where they filter harmful blue light and act as antioxidants. Population studies link higher dietary lutein/zeaxanthin to reduced risk of cataracts and age-related retinal degeneration. The American Optometric Association recognizes these carotenoids for eye health benefits.
The insoluble fiber in collard greens acts as a prebiotic, feeding beneficial gut bacteria such as Agathobacter rectalis and stimulating production of short-chain fatty acids (SCFAs) including butyrate. Collards also contain sulfoquinovose — a sulfur-containing sugar with prebiotic properties — and glucoraphanin, which may protect the stomach lining. Glucosinolate-derived isothiocyanates have anti-inflammatory effects on gut tissue.
Collard greens provide approximately 34 calories per cooked cup while delivering 7–8g of fiber, making them a high-satiety, low-energy-density food. Their low glycemic index (approximately 15) promotes stable blood glucose, reducing hunger-driving insulin surges. WebMD notes that low-GI foods help people feel fuller longer, supporting weight management.
Studies indicate that diets incorporating collard greens reduce systolic blood pressure and improve lipid profiles. Their soluble fiber binds bile acids to lower LDL cholesterol, while potassium and folate support vascular function. A study in spontaneously hypertensive rats showed that collard greens decreased systolic blood pressure and LDL cholesterol; epidemiological evidence links green leafy vegetable intake to a ~16% reduction in cardiovascular disease risk.
Collard greens are among the richest natural sources of folate (dark leafy greens per WebMD), and folate is the primary dietary determinant of plasma homocysteine. Elevated homocysteine is an established biomarker for cardiovascular risk; dietary folate from vegetables has been shown in a controlled trial to significantly decrease plasma homocysteine concentrations in humans. WeightWatchers cites that collard greens' folate lowers blood levels of homocysteine, linked to heart disease and arterial hardening.
Collard greens contain glucosinolates and methyl cysteine sulfoxides that activate hepatic phase II detoxification enzymes (glutathione S-transferases), facilitating conjugation and elimination of carcinogens and xenobiotics. Collards also boost glutathione — the body's primary antioxidant — which is required for liver neutralization of toxins. A 12-week RCT in 391 adults consuming cruciferous vegetables showed significantly increased urinary excretion of benzene carcinogens compared to placebo.
Collard greens provide approximately 14.6mg of lutein plus zeaxanthin per cooked cup — carotenoids that accumulate in the macula and retina to protect against oxidative damage and blue-light toxicity associated with AMD. The CAREDS study (PubMed 16908818, n=1,787 women) found significantly reduced odds of intermediate AMD in women under 75 with high lutein/zeaxanthin intake. AREDS2 clinical trial data also support the protective role of these carotenoids.
Collard greens provide approximately 27% DV calcium and over 883% DV vitamin K per cooked cup. Vitamin K activates osteocalcin and other bone-building proteins necessary for calcium incorporation into bone mineral. Low vitamin K intake has been linked observationally to increased fracture risk, and research supports adequate calcium intake as protective against osteoporosis and fractures.
Collard greens are among the best natural sources of folate, and adequate folate intake during early pregnancy is strongly evidence-based to prevent neural tube defects such as spina bifida. Doctors recommend at least 400mcg folate daily for women who may become pregnant. Collards also provide iron, calcium, and vitamin C relevant to maternal and fetal health.
Body systems that Collard may help support.
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