Kale is often labeled a “superfood,” and for good reason. It is one of the most nutrient-dense foods on the planet. A member of the cabbage family, kale is related to cruciferous vegetables like cabbage, broccoli, cauliflower, collard greens, and Brussels sprouts. While it has become a trendy ingredient in smoothies and salads in recent years, its history as a dietary staple goes back centuries. There are many different types of kale. The leaves can be green or purple and have either a smooth or curly shape. The most common type, called curly kale or Scots kale, has green and curly leaves and a hard, fibrous stem.
In this article, we will explore the science behind kale, breaking down its nutritional profile and explaining exactly why it is so beneficial for your health. Whether you are looking to boost your immune system, improve your skin, or manage your weight, understanding the power of this leafy green is the first step.
1. A Nutritional Powerhouse
Kale is incredibly popular among health-conscious individuals because it provides a massive amount of nutrients for very few calories. It is loaded with vitamins, minerals, and bioactive compounds that the body needs to function optimally. A single cup of raw kale (about 67 grams or 2.4 ounces) contains ample amounts of Vitamin A (from beta-carotene), Vitamin K, and Vitamin C.
In addition to these vitamins, kale is a rich source of minerals that many people do not get enough of. It contains manganese, calcium, copper, potassium, and magnesium. It is essential to understand that kale contains very little fat, but a large portion of the fat in it is an omega-3 fatty acid called alpha-linolenic acid. Given its incredibly low calorie count, kale is one of the most nutrient-dense foods in existence. Eating more whole foods like kale is a cornerstone of improving overall nutrient density in your diet.
According to the U.S. Department of Agriculture (USDA), one cup of raw kale provides well over 100% of the Daily Value (DV) for Vitamin K, making it one of the best plant-based sources available.
2. Loaded With Powerful Antioxidants
Many of the health benefits associated with kale are attributed to its content of antioxidants. Antioxidants are substances that help counteract oxidative damage by free radicals in the body. Oxidative damage is believed to be among the leading drivers of aging and many chronic diseases, including cancer. But antioxidants do much more than just fight free radicals; they have specific biological functions.
Kale is very high in antioxidants, including beta-carotene and Vitamin C, as well as various flavonoids and polyphenols. The most studied flavonoids in kale are quercetin and kaempferol. These substances have been studied intensely in test tubes and animals. They have powerful heart-protective, blood pressure-lowering, anti-inflammatory, anti-viral, anti-depressant, and anti-cancer effects. By incorporating kale into your meals, you are naturally adopting an anti-inflammatory diet strategy which can have long-term benefits for chronic disease prevention.
Research published by the National Institutes of Health (NIH) highlights how quercetin acts as a potent scavenger of free radicals, further solidifying the importance of including flavonoid-rich foods in your daily routine.
3. An Excellent Source of Vitamin C
Vitamin C is an important water-soluble antioxidant that serves many vital functions in the body’s cells. For example, it is necessary for the synthesis of collagen, the most abundant structural protein in the body. Collagen is what gives structure to your skin, hair, and bones. Kale is actually one of the world’s best sources of vitamin C. A single cup of raw kale contains more vitamin C than a whole orange.
This high Vitamin C content also aids in the absorption of iron. If you are struggling with energy levels, you might want to read more about identifying signs of iron deficiency, as pairing iron-rich foods with Vitamin C sources like kale can significantly improve absorption rates. This is particularly important for vegetarians and vegans who rely on non-heme iron.
4. Can Help Lower Cholesterol and Reduce Heart Disease Risk
Cholesterol has important functions in the body. For one, it is used to make bile acids, which are substances that help us digest fats. The liver turns cholesterol into bile acids, which are then released into the digestive system whenever you eat a fatty meal. When all the fat has been absorbed and the bile acids have served their purpose, they are reabsorbed into the bloodstream and used again.
Substances called bile acid sequestrants can bind bile acids in the digestive system and prevent them from being reabsorbed. This reduces the total amount of cholesterol in the body. Kale contains bile acid sequestrants, which can lower cholesterol levels. This might lead to a reduced risk of heart disease over time. Interestingly, a study found that steaming kale dramatically increases the bile acid-binding effect. Steamed kale is actually 43% as potent as cholestyramine, a cholesterol-lowering drug. For those looking to manage their heart health naturally, learning about natural ways to lower cholesterol is vital, and kale fits perfectly into that plan.
The link between leafy greens and cardiovascular health is well-documented. According to the American Heart Association, a diet rich in fruits and vegetables, particularly leafy greens, is associated with a lower risk of cardiovascular events.
5. Vitamin K: Essential for Blood Clotting
Vitamin K is one of the world’s most misunderstood nutrients. It is absolutely critical for blood clotting, and it does this by “activating” certain proteins and giving them the ability to bind calcium. The well-known anticoagulant drug Warfarin works by blocking the function of this vitamin. Kale is one of the world’s best sources of vitamin K, with a single raw cup containing almost 7 times the recommended daily amount.
The form of vitamin K in kale is K1, which is different from vitamin K2. K2 is found in fermented soy foods and certain animal products. While K1 is primarily involved in blood clotting, it also plays a role in bone health. If you are interested in the different roles of vitamins, check out our guide on the differences between Vitamin K1 and K2. It is generally safe for most people to eat as much Vitamin K1 as they like, but those on blood thinners must be cautious.
Information from the NIH Office of Dietary Supplements confirms that adequate Vitamin K intake is also linked to improved bone health and reduced fracture risk.
6. Numerous Cancer-Fighting Substances
Cancer is a terrible disease characterized by the uncontrolled growth of cells. Kale is loaded with compounds that are believed to have protective effects against cancer. One of these is sulforaphane, a substance that has been shown to help fight the formation of cancer at the molecular level. It also contains indole-3-carbinol, another substance that is believed to help prevent cancer. Studies have shown that cruciferous vegetables (including kale) may significantly lower the risk of several cancers, although the evidence in humans is mixed.
These phytonutrients work by altering the way the liver metabolizes potential carcinogens. Incorporating kale into a diet rich in other cancer-fighting foods creates a synergistic effect that boosts your body’s defense systems. The sheer density of glucosinolates in kale makes it a top contender in oncology nutrition research.
According to the National Cancer Institute, glucosinolates in cruciferous vegetables break down into biologically active compounds like indoles and isothiocyanates, which have demonstrated anticancer effects in animal studies.
7. Supports Eye Health
One of the most common consequences of aging is that eyesight gets worse. Fortunately, there are several nutrients in the diet that can help prevent this from happening. Two of the main ones are lutein and zeaxanthin, carotenoid antioxidants that are found in large amounts in kale and some other foods. Many studies have shown that people who eat enough lutein and zeaxanthin have a much lower risk of macular degeneration and cataracts, two very common eye disorders.
These antioxidants act like natural sunglasses, filtering out harmful blue light and protecting the delicate structures of the retina. If you are concerned about vision loss, reading about essential nutrients for maintaining eye health will provide you with a broader list of foods to include in your diet alongside kale.
The National Eye Institute supports the finding that high dietary intake of lutein and zeaxanthin is associated with a lower risk of advanced age-related macular degeneration.
8. Weight Loss and Digestion
Kale has several properties that make it a weight-loss-friendly food. It is very low in calories but still provides significant bulk that should help you feel full. Because of the low calorie and high water content, kale has a low energy density. Eating plenty of foods with a low energy density has been shown to aid weight loss in numerous studies. Kale also contains a small amount of protein and fiber.
Fiber is crucial for maintaining a healthy digestive tract and regulating blood sugar levels. By slowing down digestion, fiber helps prevent the spikes and crashes in insulin that lead to hunger cravings. For those looking for meal inspiration, our high-fiber smoothie recipes often feature kale as a primary ingredient because it blends well without adding excess sugar.
According to the Centers for Disease Control and Prevention (CDC), substituting high-calorie foods with lower-calorie vegetables that contain water and fiber is a key strategy for successful weight management.
How to Select and Store Kale
To get the most out of your kale, look for bunches with dark, crisp leaves. Avoid yellowing or wilting leaves, as these indicate the vegetable is past its prime. Smaller leaves will generally be more tender and have a milder flavor than large, tough leaves. Store kale in the refrigerator in a plastic bag, removing as much air as possible. It can stay fresh for up to 5 days. You can also wash and dry the leaves before storing them to make meal prep faster.
9. Potential Side Effects and Interactions
While kale is a superstar vegetable, it is not suitable for everyone in unlimited quantities. Kale contains goitrogens, which are substances that can interfere with the function of the thyroid gland. This is usually not a problem for healthy people, but it can be an issue for those with thyroid conditions. Cooking kale helps deactivate some of these enzymes.
Additionally, because of the high Vitamin K content, people taking blood-thinning medication like Warfarin (Coumadin) need to be careful. The medication works by inhibiting Vitamin K, so a sudden increase in kale intake can render the drug less effective. It is vital to consult your doctor if you are on medication. You can learn more about common food-drug interactions on our blog to ensure you are eating safely.
The American Thyroid Association notes that while cruciferous vegetables are healthy, those with compromised thyroid function should consume them in moderation and preferably cooked.
10. Mineral Deficiency Solution
Modern diets are often high in processed foods and low in essential minerals. Kale is a good source of minerals that most people are missing. It is a good plant-based source of calcium, a nutrient that is very important for bone health and plays a role in all sorts of cellular functions. It is also a decent source of magnesium, an incredibly important mineral that most people don’t get enough of. Eating plenty of magnesium may be protective against type 2 diabetes and heart disease.
Kale also contains potassium, a mineral that helps maintain electrical gradients in the body’s cells. Adequate potassium intake has been linked to reduced blood pressure and a lower risk of heart disease. To understand how these minerals work together, read our article on the importance of electrolytes and hydration.
A study published in the The Lancet highlights the global health implications of low fruit and vegetable intake, emphasizing the need for mineral-rich foods like kale to combat non-communicable diseases.
How to Add More Kale to Your Diet
Adding kale to your diet is relatively easy. You can simply add it to your salads or use it in recipes. A popular snack is kale chips, where you drizzle some extra virgin olive oil or avocado oil on your kale, add some salt, and then bake in an oven until dry. It tastes absolutely delicious and makes a great crunchy, super-healthy snack. Many people also add kale to their smoothies in order to boost the nutritional value.
If you find the texture of raw kale too tough, try “massaging” it. Drizzle a little olive oil and lemon juice on the leaves in a bowl and rub them with your hands for 2-3 minutes. This breaks down the cellulose structure, making the leaves softer and sweeter. For dinner ideas, check out our collection of easy weeknight plant-based meals where kale takes center stage.
Finally, steaming kale is a great way to preserve its nutrients while making it easier to digest. Avoid boiling it for long periods, as water-soluble vitamins like Vitamin C and B vitamins will leach out into the water. According to the Harvard T.H. Chan School of Public Health, varied preparation methods can help you enjoy kale without getting bored of the flavor.
The Bottom Line
Kale is definitely one of the healthiest and most nutritious foods on the planet. It is loaded with vitamins, minerals, antioxidants, and various bioactive compounds. It supports heart health, eye health, immune function, and may even help protect against cancer. While those on blood thinners or with thyroid issues should proceed with caution, for the vast majority of people, kale is a safe and incredibly beneficial addition to the diet.
If you want to dramatically boost the nutrient content of your diet, adding kale is one of the easiest and most effective strategies you can employ. For a holistic approach to wellness, consider pairing your healthy diet with regular exercise; see our guide on combining nutrition and exercise for optimal health.
