Dr. Andrea Middleton - Is It Bad For You? Approved by Dr. Andrea Middleton

Are Collard Greens Bad For You?



Short answer

Collard greens are a nutrient-rich vegetable, with benefits such as aiding in weight management, supporting digestive health, and providing essential vitamins and minerals. They are not bad for you and can be part of a healthy diet. However, their vitamin K content can interact with blood thinners, and their oxalates might contribute to kidney stone risks for susceptible individuals. Cooking can reduce negative effects, making them a safe choice for most people.



Long answer

Nutritional Profile of Collard Greens

Collard greens, a cruciferous vegetable that hails from the same family as kale, broccoli, and Brussels sprouts, have a rich nutritional profile that contributes to their many health benefits. This leafy green is packed with vitamins, minerals, fiber, and antioxidants, making it an excellent addition to a healthy diet.

Let's break down the nutrients found in a one-cup serving (about 190 grams) of boiled and drained collard greens, without added salt:

  • Calories: A low-calorie option, collard greens contain approximately 49 calories per cup, making them ideal for weight management.
  • Fiber: With about 5 grams of dietary fiber, collard greens can help support digestive health and promote a feeling of fullness.
  • Protein: Collard greens offer around 4 grams of protein, which is relatively high for leafy greens, contributing to muscle maintenance and growth.
  • Vitamins: They are exceptionally rich in vitamin K, providing over 1000% of the Recommended Daily Intake (RDI) in a single cup. This is crucial for blood clotting and bone health. They are also high in vitamin A (providing about 308% of RDI), which supports vision and immune function, and vitamin C (58% of RDI), an antioxidant promoting skin health and immune function.
  • Minerals: A great source of calcium, collard greens contain about 266 milligrams per cup, which is essential for bone health and muscle function. They also provide significant amounts of manganese, iron, magnesium, and potassium, which are vital for metabolic functions, oxygen transport, nerve health, and blood pressure regulation, respectively.
  • Antioxidants: Rich in antioxidants like beta-carotene, lutein, and zeaxanthin, these compounds help protect the body against oxidative stress and may reduce the risk of chronic diseases.

It is important to note that some nutrients, like vitamin C, can be reduced during cooking, especially when boiling. Steaming or sautéing collard greens might retain more nutrients compared to boiling them. Additionally, fat-soluble vitamins like vitamin K are better absorbed when consumed with a source of fat.

The following table offers a concise summary of the essential nutrients found in one cup of boiled collard greens:

Nutrient Amount % RDI*
Calories 49 N/A
Fiber 5 g 20%
Protein 4 g 8%
Vitamin K 1042 mcg 1302%
Vitamin A 17707 IU 354%
Vitamin C 34.6 mg 58%
Calcium 266 mg 27%
Iron 2.2 mg 12%
Magnesium 40 mg 10%
Potassium 220 mg 6%
Manganese 0.99 mg 50%

* Percentages are based on a 2000 calorie diet

Given their robust nutrient content, it's clear that collard greens can be a nutritious addition to a balanced diet. However, how one integrates them into meals and the accompanying ingredients can also influence their overall nutritional impact.

Thyroid Function and Goitrogenic Effects in Collard Greens

When it comes to discussing the impact of collard greens on thyroid function, it is crucial to understand the concept of goitrogens. These are substances that can disrupt the production of thyroid hormones by interfering with iodine uptake in the thyroid gland. Collard greens, along with other cruciferous vegetables like broccoli, kale, and cabbage, naturally contain goitrogens. However, the context and the amount of consumption are key factors in determining their actual impact on thyroid health.

Let's dive into the science behind goitrogens and how they interact with the thyroid:

  • Glucosinolates: This is the compound in collard greens and other cruciferous vegetables that can yield goitrogenic effects when consumed in very large quantities. Upon ingestion, glucosinolates can be converted into isothiocyanates, which have been shown to interfere with thyroid hormone synthesis.
  • Iodine deficiency: The goitrogenic effects of collard greens are mostly a concern if there is an existing iodine deficiency. When thyroid glands lack sufficient iodine, consuming high amounts of goitrogens can contribute to the development of goiter and other thyroid-related issues.
  • Cooking and its impact: Cooking can significantly reduce the goitrogenic potential of collard greens. Methods like steaming, boiling, or fermenting can decrease the levels of glucosinolates, hence reducing the risk of affecting thyroid function.
  • Dietary context: The effects of goitrogens are generally mitigated by a balanced diet that is rich in iodine. For those who consume adequate levels of iodine, the intake of collard greens should not pose a threat to thyroid health.

Research provides perspective on this issue:

  • A study published in The Journal of Nutrition suggests that moderate consumption of cruciferous vegetables does not increase the risk of thyroid cancer or other thyroid diseases in individuals with adequate iodine intake.
  • Another study in Nutrition Reviews concluded that the potential health benefits of cruciferous vegetables like collard greens often outweigh the risks associated with their goitrogenic compounds.
  • Experts from the Linus Pauling Institute at Oregon State University have noted that a diet containing a variety of vegetables is essential for health and that the focus should be on diversification rather than elimination.

In essence, while collard greens contain compounds that can affect thyroid function when consumed in excessive amounts or in the presence of an iodine deficiency, they are generally considered safe for consumption. Cooking these greens can further alleviate concerns, making them a nutritious addition to a balanced diet. As always, when considering dietary choices and thyroid health, it is best to consult a healthcare provider or a registered dietitian for personalized advice.

Potential Interaction with Blood Thinning Medications

Collard greens, the nutritious leafy vegetables often associated with Southern cuisine, are a rich source of vitamins and minerals. However, it is crucial for individuals on blood-thinning medications, such as warfarin (Coumadin), to be aware of their vitamin K intake. While collard greens offer numerous health benefits, they are also high in vitamin K, which plays a key role in blood clotting processes. The consistency of vitamin K intake is imperative for the effectiveness and safety of warfarin therapy.

Warfarin works by inhibiting the recycling of vitamin K, thereby prolonging the time it takes for blood to clot. An intake of vitamin K that is higher than usual can counteract the effects of warfarin, leading to a risk of blood clots. Conversely, a significant decrease in vitamin K intake can enhance the effects of warfarin, increasing the risk of bleeding. Hence, maintaining a stable intake of vitamin K is essential when on these medications.

It is important for those on warfarin to:

  • Consult with their healthcare provider about their diet and the use of warfarin.
  • Monitor their vitamin K intake and keep it consistent day to day.
  • Be educated about foods high in vitamin K and how to balance them within their dietary intake.
  • Understand that moderation is key – rather than eliminating collard greens completely, they can be consumed in controlled amounts as part of a well-balanced diet.
  • Consider getting their INR (International Normalized Ratio) levels checked regularly to ensure blood clotting times remain in the therapeutic range.

A study published in The American Journal of Medicine has indicated that sudden changes in vitamin K intake can lead to a significant alteration in INR values among individuals taking warfarin. Additionally, patient education on dietary vitamin K has been linked to more stable INR control, as per research in the Journal of Thrombosis and Thrombolysis.

In summary, collard greens are not inherently bad for individuals on blood-thinning medications, but they should be consumed with care and awareness of their potential interactions. It is vital to engage in a dialogue with healthcare providers to ensure safe dietary practices and effective medication management.

Oxalates in Collard Greens and Risk of Kidney Stones

Collard greens are a nutrient-dense leafy vegetable that are an excellent source of vitamins, minerals, and dietary fiber. However, they also contain compounds called oxalates, which can contribute to kidney stone formation in some individuals. Oxalates are natural substances found in many plants, nuts, seeds, and chocolate. In the body, oxalates can bind with minerals to form compounds, such as calcium oxalate, which is the most common type of kidney stone.

Oxalates on their own are not inherently bad, but in patients with a history of oxalate kidney stones, consuming high-oxalate foods like collard greens might elevate the risk. The digestive system of some individuals may not process oxalates effectively, leading to the accumulation of these compounds in the kidney, where they can crystallize and form stones.

Research suggests a correlation between high dietary intake of oxalates and the formation of kidney stones. A study in the New England Journal of Medicine reported that individuals who are prone to forming calcium oxalate stones should reduce their oxalate intake to mitigate risk. However, it also highlighted the importance of dietary calcium, which can bind to oxalates in the gastrointestinal tract, thereby reducing their absorption and subsequent excretion in urine.

For those concerned about oxalate intake, the following measures might be helpful:

  • Increasing fluid intake, particularly water, to help flush out oxalates from the kidneys.
  • Consuming calcium-rich foods alongside high-oxalate foods to reduce oxalate absorption.
  • Limiting other high-oxalate foods, especially if you are at risk for kidney stones, such as spinach, beets, and certain nuts and beans.
  • Consulting with a healthcare provider or dietary specialist to individualize dietary recommendations based on personal health history and needs.

It's worth noting that the risk associated with oxalate intake varies considerably among individuals. Factors that may influence risk include genetic tendencies, hydration status, dietary habits, and other health conditions. Therefore, moderate consumption of collard greens, complemented by a balanced and hydrating diet, may still be safe and beneficial for many people, even those with a propensity for kidney stones. Consulting with a nutritionist or healthcare provider can provide personalized advice and strategies to enjoy collard greens without significantly increasing the risk of kidney stones.

Additionally, cooking methods can impact the oxalate content of collard greens. Studies indicate that boiling vegetables can significantly reduce their oxalate content as the water-soluble oxalates leach into the cooking water. Therefore, choosing the right preparation method could be a strategic approach to enjoying collard greens while mitigating the risk of kidney stones.

Frequently asked questions

To maximize the nutritional value of collard greens, steaming or sautéing is recommended over boiling. These methods help retain more vitamins, especially vitamin C, and reduce the loss of other water-soluble nutrients.

Yes, collard greens are an excellent plant-based source of calcium, providing about 266 milligrams per cup. This makes them a valuable addition to vegetarian and vegan diets for maintaining bone health and muscle function.

Individuals with thyroid concerns should ensure they have adequate iodine intake and cook collard greens to reduce goitrogenic compounds. Consuming these greens in moderation and consulting with a healthcare provider can help manage potential effects on thyroid function.

People with a history of kidney stones should approach collard greens with caution due to their oxalate content. Boiling collard greens can reduce oxalate levels, and consuming them with calcium-rich foods might lower the risk. It's best to consult with a healthcare provider for individual dietary advice.

Ask a question about Collard Greens and our team will publish the answer as soon as possible.

Possible long-term side effects

  • goiter
  • thyroid dysfunction
  • blood clotting issues
  • increased risk of kidney stones

Ingredients to be aware of

  • goitrogens
  • vitamin k
  • oxalates


  • low in calories
  • high in fiber
  • good source of protein
  • rich in vitamins a, c, k
  • contains calcium
  • contains minerals: manganese, iron, magnesium, potassium
  • antioxidants: beta-carotene, lutein, zeaxanthin

Healthier alternatives

  • steamed or sautéed collard greens
  • balanced diet rich in iodine
  • low-oxalate vegetables

Thank you for your feedback!

Written by Diane Saleem
Published on: 02-27-2024

Thank you for your feedback!

Written by Diane Saleem
Published on: 02-27-2024

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