Kale has become an incredibly popular leafy green in recent years, hailed for its impressive nutritional profile. It’s high in fiber, vitamins A, C, and K, calcium, potassium, magnesium, and antioxidants. Some of the potential health benefits of kale include improved heart health, reduced inflammation, anti-cancer effects, better blood sugar control, and aid with weight loss.
With the rise in popularity of juicing, many people are blending up raw kale to pack more nutrients into their diet. Proponents claim that juicing helps concentrate the beneficial plant compounds in kale while removing the fiber, making the nutrients easier to absorb. However, others argue that juicing strips away much of the beneficial fiber content of kale that is important for health.
So should you be drinking raw kale juice? Can you gain the same benefits of eating kale by juicing it instead? This article examines the evidence behind the potential benefits and downsides of drinking raw kale juice.
Nutrition Profile of Kale
First, let’s take a look at why kale is considered one of the healthiest vegetables around.
One cup (67 grams) of raw kale contains just 33 calories yet packs impressive amounts of vitamins and minerals:
|% Daily Value
As you can see, kale provides high amounts of vitamin K, vitamin A, vitamin C, and also contains a decent amount of calcium, potassium, magnesium and manganese.
The two carotenoids found in kale, lutein and zeaxanthin, are incredibly important for eye health and have been linked to reduced risk of macular degeneration and cataracts.
Additionally, kale contains cancer-fighting compounds called glucosinolates, which form bioactive compounds like sulforaphane when kale is chopped or chewed. These compounds have been studied extensively for their ability to protect against cancer.
Kale also provides polyphenols like quercitin and kaempferol, which have strong anti-inflammatory effects in the body. And with just 33 calories per cup, kale is incredibly nutritious while still being low in calories.
Benefits of Eating Raw Kale
Eating kale raw, such as in salads, smoothies, or juiced, may provide the most nutritional bang for your buck. Here are some of the key benefits associated with consuming raw kale:
Higher Nutrient Content
Several nutrients in kale are sensitive to heat and degrade when cooked. For example, one study showed that boiling kale for just 5 minutes can reduce the amount of vitamin C by 25% (1).
Steaming kale for 15 minutes has also been shown to significantly decrease vitamin K content (2).
Additionally, some studies have found that raw kale has a higher amount of cancer-fighting compounds like sulforaphane compared to cooked kale (3).
Therefore, to maximize the nutrient content of kale, it’s best consumed raw.
The fiber content of vegetables decreases significantly when cooked.
Fiber moves through the digestive system undigested and offers many beneficial effects. It helps regulate bowel movements, lowers cholesterol, controls blood sugar levels, and feeds the beneficial bacteria in the gut (4).
A high intake of dietary fiber has also been associated with a lower risk of heart disease, diabetes, and certain types of cancer (5, 6, 7).
One study showed that cooking kale reduces its insoluble fiber content by nearly 50% (8). Insoluble fiber adds bulk to stool and speeds the passage of food through the digestive system.
Because insoluble fiber is reduced with cooking, consuming raw kale maximizes fiber intake.
As mentioned previously, kale contains compounds called glucosinolates, which have been studied extensively for their anti-cancer effects.
Studies show that steps like chopping, blending, and chewing cruciferous vegetables like kale helps activate these compounds (9).
However, some early research also indicates that allowing kale to sit after chopping for at least 5 minutes before heating or mixing it further enhances glucosinolate activation (10).
So while raw kale prioritizes glucosinolate activation, allowing chopped kale to rest before consuming may maximize the formation of these beneficial compounds.
Better Absorption of Fat-Soluble Vitamins
The fat-soluble vitamins A, D, E, and K are best absorbed when consumed with dietary fat.
While cooking kale in oil can help boost absorption, simply drizzling some olive oil over raw kale is an easy way to maximize nutrient absorption.
One study even showed that absorption of beta-carotene from raw vegetables was 6.5 times greater when consumed with fat versus fat-free salad dressing (11).
So to best absorb the fat-soluble vitamins in kale, consume it raw alongside a healthy fat like olive oil or avocado.
Downsides of Juicing Kale
While juicing raw kale allows you to take in a concentrated dose of its various micronutrients, there are some downsides to consider as well. Here are some of the drawbacks of drinking raw kale juice regularly:
Loss of Fiber
Juicing strips away the insoluble and soluble fiber content of kale, leaving only the nutrients behind in the juice.
This is detrimental because fiber is vital to digestive health and linked to a multitude of benefits, including reduced cholesterol, stabilized blood sugar levels, and lower risk of chronic disease (4).
Juicing once in a while isn’t a big concern, but replacing whole fruits and vegetables with only juice can have negative consequences due to inadequate fiber intake.
High in Oxalates
Kale contains compounds called oxalates, which can bind to minerals like calcium and iron in the body and prevent them from being absorbed (12).
Cooking kale helps reduce the oxalate content, while juicing concentrates these anti-nutrients (13).
For most people, oxalates from a varied diet are not an issue. However, for those prone to kidney stones or with a health condition that inhibits mineral absorption, the high oxalate levels in kale juice could potentially cause problems.
Blood Sugar Spikes
Due to its low fiber content, drinking fruit and vegetable juices like kale juice can spike blood sugar levels.
Fiber helps slow the absorption of sugar into the bloodstream, which is important for maintaining steady blood sugar levels, especially for those with diabetes (14).
Compared to eating whole kale, drinking kale juice causes a more rapid rise in blood sugar. Over time, frequent spikes can take a toll on health.
Nutrient Loss from Oxidation
Juicing subjects vegetables and fruits to oxidation, which can degrade certain nutrients over time.
For example, an analysis of vegetable juices found that juicing causes a significant decrease in the amount of vitamin C and carotenoids (15).
One study showed that vitamin C levels declined by 24% in juices made from a combination of fruits and vegetables after 8 hours of storage (16).
To minimize nutrient degradation, it’s best to drink fresh juices right away rather than saving them for later.
Who Should Avoid Raw Kale Juice?
While drinking kale juice a few times per week is unlikely to cause issues for most healthy people, those with certain health conditions may want to minimize consumption or avoid it altogether.
– Those with kidney problems or a history of kidney stones
– Individuals taking blood thinners
– Anyone with an underactive thyroid (hypothyroidism)
– People unable to properly absorb minerals like calcium or iron
Additionally, check with your doctor if you are undergoing chemotherapy treatment, as compounds in kale may interact with certain drugs used for cancer.
Pregnant women should also limit juicing to an occasional treat. Getting adequate fiber, protein, and fat from whole foods is important during pregnancy.
How Much Kale Juice is Safe to Drink Daily?
There’s no official recommendation for how much kale juice is safe or advisable to drink each day.
Like most things in nutrition, moderation is key. While juicing every now and then likely poses no issues for most, regularly replacing meals with green juices could have negative side effects.
For healthy adults, sticking to 8 ounces (230 ml) or less of kale juice 2–3 times per week is a safe amount that can help increase your nutrient intake when paired with a balanced diet.
Drinking more than this on a regular basis may not provide much additional benefit and could even inhibit mineral absorption or lead to issues due to excess oxalate or vitamin K intake in some cases.
It’s best to focus on getting your nutrients, fiber, protein, and healthy fats from whole foods like fruits, vegetables, nuts, seeds, and quality sources of protein. Use juicing as a supplement to your diet rather than a meal replacement.
Look for recipes that combine kale with fruits, carrots, tomatoes, or cucumber to help dilute the stronger, bitter taste. You can also add a squeeze of lemon to help cut the earthy flavor.
Kale is one of the most nutritious vegetables you can eat. Juicing kale allows you to take in a concentrated dose of its various vitamins, minerals, and beneficial plant compounds.
However, juicing also strips away kale’s fiber content, which is linked to many health benefits. Drinking raw kale juice also provides anti-nutrients like oxalates and may spike blood sugar levels in large amounts.
For most people, drinking a reasonable amount of fresh kale juice two to three times per week is unlikely to cause problems. However, those with certain health conditions may want to avoid juicing kale.
To maximize the nutritional value of kale, it’s best to consume it lightly cooked or raw as part of a balanced diet, rather than relying on juicing. Focus on getting fiber, protein, and healthy fats from whole foods and use kale juice as an occasional nutritional boost.