Kale: Does it Deserve the Hype?

Written By: Xavier Oyola and Laila Ibrahim

 Over the past decade or so, kale went from an obscure garnish to the unofficial symbol of clean eating. You've seen it in smoothies, salads, chip form, and probably blended into something that costs twelve dollars at a juice bar. The hype isn't entirely wrong. Kale is genuinely one of the most nutrient-dense vegetables you can eat. But the conversation around it has gotten so loud and so one-sided that a few important nuances have gotten buried, including the fact that for certain people, eating too much of it can potentially cause problems.

Kale belongs to the same cruciferous family as broccoli, cabbage, and Brussels sprouts. A single serving is super nutrient dense,  packing vitamins A, C, and K, along with calcium, iron, potassium, and dietary fiber. Research has found that kale provides higher bioavailability of calcium than milk, which surprises most people. It also contains antioxidants like quercetin and kaempferol, which studies link to reduced inflammation and a lower risk of chronic disease. One 2016 study found that in 149 people with metabolic syndrome, consuming 14 grams of kale powder daily for eight weeks significantly reduced LDL cholesterol levels, along with blood pressure, belly fat, and fasting blood sugar levels. For the average healthy person eating a varied diet, adding kale regularly is a straightforward win.

Where things get more complicated is when kale stops being one part of a balanced plate and starts being treated like a cure-all to eat in unlimited quantities. The same compounds that give kale many of its benefits can, in excess, work against you.

Take the thyroid concern, which has circulated online for years and scared a lot of people off kale entirely. The worry centers on goitrogens, compounds found in cruciferous vegetables that can interfere with how the thyroid absorbs iodine. The common curly and lacinato varieties sold in most grocery stores contain less than 10 micromoles of goitrin per 100-gram serving, well below the 194 micromoles shown to actually inhibit thyroid function. For the vast majority of people eating normal portions of standard kale varieties, thyroid disruption is not a realistic concern. Cooking kale also significantly reduces its goitrogenic properties, so if you have an existing thyroid condition, lightly steaming or sauteing your kale rather than eating it raw in large amounts is a reasonable precaution.

The kidney stone connection is another misconception worth unpacking. Kale contains only about 17 milligrams of oxalate per serving, compared to the hundreds of milligrams found in spinach and Swiss chard. Researchers have said it is essentially impossible to eat enough kale to cause kidney stones from oxalate alone. If you have a personal or family history of kidney stones, your doctor may recommend rotating your leafy greens rather than relying on one exclusively, but kale is far from the worst offender in this category.

The one area where caution is genuinely warranted involves people taking blood thinning medications like warfarin. Kale is extremely high in vitamin K, which promotes blood clotting and works against what warfarin is designed to do. The key is consistency: eating roughly the same amount of vitamin K-rich foods from week to week helps keep your medication dose properly calibrated. Sudden large increases or decreases in kale intake can throw off your clotting levels. If you take a blood thinner and want to include kale in your diet, the solution is not to avoid it entirely but to talk to your prescriber and keep your intake steady.

Beyond these specific populations, the most common issue people run into with kale is simply digestive discomfort. Its high fiber content can cause bloating and gas, particularly when eaten raw in large quantities on an empty stomach. This is not dangerous, but it is a good reminder that more is not always better, even with vegetables. Varying your greens throughout the week is both safer and more nutritious than treating any single food as a daily staple in enormous amounts.

References:

Guo, C., et al. (2020). Kale: Review on nutritional composition, bio-active compounds, anti-nutritional factors, health beneficial properties and value-added products. Cogent Food and Agriculture, 6(1). https://www.tandfonline.com/doi/full/10.1080/23311932.2020.1811048

Fernandes, F., & Valentão, P. (2021). Extraction and natural bioactive molecules characterization in spinach, kale and purslane: A comparative study. Molecules, 26(9). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8123472/

ScienceInsights. (2026, April 28). Is kale good for you? Benefits and side effects. https://scienceinsights.org/is-kale-good-for-you-benefits-and-side-effects/