Spinach Loses Most of Its Vitamin C When Heated
Think spinach is the ultimate superfood? Raw spinach certainly packs a nutritional punch with its impressive vitamin C content, but here’s what nobody tells you. Spinach can lose much of its vitamin C when cooked. Blanching for five minutes can more than halve vitamin C levels, with more than 90 percent dissolving into the cooking water after 15 minutes. That vibrant green power you’re expecting from your cooked spinach dishes? Most of it literally goes down the drain with the cooking water. Some water-soluble vitamins can be lost when spinach or kale are cooked using water-heavy methods, such as boiling, or when they come into contact with oil, like sauteing. Yet countless recipes still call for wilted spinach, sautéed spinach, or blanched spinach as if they’re delivering the same nutritional value as the raw leaves. Spinach contains large amounts of dietary oxalate, a compound that binds to calcium in your body, preventing its absorption. Eating oxalate-rich foods also increases the excretion of oxalate through your urine, which can lead to the formation of calcium oxalate kidney stones.
Kale’s Vitamin C Takes a Major Hit From Heat
“If you were to boil kale, you’re going to have heat, and heat will denature the antioxidants, so vitamin C will get destroyed. Basically, it will leach into the water,” Sherry Gray, MPH, RD, a registered dietitian and extension educator at the University of Connecticut, told Verywell. Raw kale contains more than twice the vitamin C of spinach, making it seem like a nutritional powerhouse. But when you throw it into that trendy kale and white bean soup or massage it for a warm salad, something disappointing happens. The downside is that cooking can reduce the antioxidant and mineral content in kale, but some cooking methods are worse than others. But heat can affect the antioxidant content. Drying is especially damaging, eliminating up to 90 percent of the vitamin C, which suggests that kale chips may pale in comparison to fresh kale. Those popular kale chips you see everywhere? They’re basically crunchy green chips with a fraction of the vitamin power you’d expect.
Blueberries Lose Their Antioxidant Magic When Cooked
Everyone knows blueberries are antioxidant superstars, but here’s where things get tricky. “Antioxidants can be harmed by heat,” Zumpano explains. “But heat can affect the antioxidant content.” Those blueberry muffins, pancakes, and pies you love? They’re delicious, but they’re not delivering the same superfood benefits as fresh berries. Antioxidant activity was not reduced when using shorter microwaving times, or baking or boiling. “What we can say from this study is that cooking and heating, especially longer microwaving, does decrease the amount of beneficial compounds in the berries,” Grusak said. Heating may affect the amount of antioxidants blueberries provide. The deep blue anthocyanins that make blueberries special are heat-sensitive compounds that break down during cooking. Yet recipe after recipe calls for baking blueberries into everything from bread to crumbles, assuming you’ll get the same health benefits.
Broccoli’s Water-Soluble Vitamins Vanish in Boiling Water
Broccoli, spinach, and lettuce may lose up to 50% or more of their vitamin C when boiled. Because vitamin C is water-soluble and sensitive to heat, it can leach out of vegetables when they’re immersed in hot water. Broccoli is often touted as a cancer-fighting superfood, and while it does contain impressive compounds, cooking it the wrong way strips away much of its nutritional value. In fact, boiling reduces vitamin C content more than any other cooking method. Think about all those recipes that tell you to boil broccoli until tender – they’re essentially asking you to throw away half the nutrients. Up to 60% of thiamine, niacin, and other B vitamins may be lost when meat is simmered and its juices run off. However, when the liquid containing these juices is consumed, 100% of the minerals and 70–90% of B vitamins are retained. The irony is that many people drain and discard that vitamin-rich cooking water, thinking they’re being healthy by eating the “solid” vegetables.
Carrots’ Beta-Carotene Gets Complicated by Heat
Here’s where things get weird with carrots. Everyone knows they’re packed with beta-carotene, but cooking them creates a nutritional paradox that most people don’t understand. Cooked vegetables were occasionally higher contents of fat-soluble vitamins, including α-tocopherol and β-carotene, than that of their fresh counterparts, but it depends on the type of vegetables. While some cooking can actually make beta-carotene more available to your body, other cooking methods can damage it. Most of the beta-carotene, which is fat soluble, tends to stay in the leaves, though. The problem is that many recipes call for boiling or overcooking carrots, which can break down these beneficial compounds. Steaming and roasting tend to preserve more nutrients, but how many carrot recipes actually specify gentle cooking methods? Most just tell you to cook until soft, which often means cooking until the nutrients are compromised.
Bell Peppers Lose Their Vitamin C Crown When Heated
Red bell peppers actually contain more vitamin C than oranges – when they’re raw. But the moment you toss them into a stir-fry or roast them for that Instagram-worthy stuffed pepper dish, things change dramatically. B vitamins are similarly heat sensitive. Like other vitamin C-rich vegetables, bell peppers are incredibly vulnerable to heat and water exposure. Generally, higher retention of vitamin C was observed after microwaving with the lowest retention recorded after boiling. Steaming and microwaving retained higher concentrations of vitamin C than boiling because of the reduced contact with water at relatively low temperatures. Yet countless recipes call for sautéing, grilling, or roasting bell peppers as if they’ll maintain their superfood status. The bright colors might look appealing when cooked, but much of the nutritional firepower has been lost to heat. Those colorful pepper and onion fajitas? They’re tasty, but they’re not the vitamin bombs you might expect.
Brussels Sprouts Sacrifice Nutrients for Palatability
Brussels sprouts have had a major image makeover in recent years, going from universally hated to trendy superfood status. But here’s the catch – most of the popular preparation methods that make them actually taste good also strip away many of their beneficial compounds. Cooking may cause changes to the contents of vitamins, but it depends on vegetables and cooking processes. Those crispy, caramelized Brussels sprouts that everyone loves? They’re usually roasted at high heat for extended periods, which breaks down heat-sensitive vitamins and antioxidants. Kale is high in antioxidants, such as vitamin C, which may help fight oxidative damage to the body. Oxidative damage plays a role in many illnesses, including cancer, heart disease, and diabetes. Brussels sprouts, being in the same family as kale, face similar nutritional losses when subjected to high heat. The irony is that the cooking methods that make Brussels sprouts delicious enough for people to actually eat them also diminish their superfood status.
Sweet Potatoes’ Vitamin A Takes a Hit From Extended Cooking
Sweet potatoes are often praised for their incredible vitamin A content, and they do deserve recognition for their nutritional density. However, the way most people prepare them – baking for long periods, boiling, or frying – can significantly impact their nutrient profile. Microwaving had less of an impact on vitamin C content, with high retention (> 90%) observed for spinach, carrots, sweet potato, and broccoli. While sweet potatoes retain more of their nutrients than some other vegetables when cooked, extended high-heat cooking still causes losses. Using minimal cooking water and cooking for shorter time periods should result in higher vitamin C retention. Those popular sweet potato fries and long-baked sweet potatoes that are crispy on the outside? They’ve lost a significant portion of their water-soluble vitamins compared to quickly steamed or microwaved versions. Yet recipe after recipe calls for hour-long baking or deep frying, assuming the nutritional benefits remain intact. The caramelization that makes them taste amazing comes at a nutritional cost that most people don’t realize.
