Vegetables are a diet superstar, but many people aren’t eating enough of them. They’re also some of the most nutrient-dense foods on the planet, being an excellent source of vitamins, minerals, fiber, and antioxidants, the nutrients that support mental and physical health.
Plus, vegetables come in an array of stunning colors, making them a visual feast too. No matter what color you choose, you’ll get an abundance of vitamins, minerals, and phytonutrients that offer various health benefits.
How do you eat most of your vegetables? If you eat your veggies raw, you’ll get the most vitamin C. Of all the vitamins abundant in vegetables, vitamin C is the most fragile. Certain B vitamins are also heat sensitive. How can you cook them in a way that preserves their nutritional goodness?
Heat and Light Destroys Vitamin C
At one time, it was popular to boil vegetables until they were soft and mushy. But when you boil veggies, you expose them to heat and water, and a significant amount of the vitamin C in that veggie ends up in the cooking water. The degree to which you lose vitamin C depends on how much water you add, the temperature of the water, and how long you boil your vegetables. The quantity of vitamin C loss varies widely from 19% to 58%.
Frozen vegetables usually contain as much nutrition as fresh ones and sometimes more. That’s because freezing seals in the nutrients while fresh vegetables lose vitamins when exposed to light and heat. Studies also show that you shouldn’t thaw frozen vegetables before cooking, as it leads to an even greater loss of vitamin C. B vitamins, including thiamine and riboflavin, are also heat and light-sensitive. So, you’ll lose these vitamins too through boiling.
Boiling vegetables also reduces glucosinolate, a cancer-fighting compound in broccoli. In fact, high heat and water destroy around 77% of the glucosinolate in broccoli, based on one study, and the losses increase as boiling time increases. If you’re eating broccoli for its potential cancer-fighting phytochemicals, like glucosinolate, don’t boil it.
Additionally, boiling destroys myrosinase, an enzyme that activates glucosinolates. Activation converts it into a compound called sulforaphane with anti-cancer properties. Thus, myrosinase is necessary for the full benefits of broccoli – another reason not to boil broccoli. You won’t get the full benefits from boiled broccoli.
Certain vegetables are susceptible to nutrient loss with boiling. One study found that cauliflower, peas, and zucchini lost over half of their antioxidants when boiled. Boiling also does little to improve the flavor of vegetables, so it’s the least desirable way to prepare them.
What Are Better Methods for Cooking Vegetables?
If you’re in a hurry, you might wonder how you get veggies on the table fast while still preserving their nutrients. One method supported by science is steaming vegetables in a bamboo or metal steamer. With this method, the vegetables aren’t immersed in water, and the veggies don’t have direct contact with water, only steam. You’ll preserve much more vitamin C using this method than you will by boiling them.
Surprisingly, microwaving vegetables is an effective way to preserve a veggie’s nutrients. Because the cooking time is short, you don’t get a substantial loss of nutrients. The key is to use as little water as possible and keep the cooking time short.
Also, don’t chop vegetables into small pieces before microwaving, since that increases the surface area exposed to water and can lead to the leaching of vitamins into the water. You can also save the microwave water and use it to make a sauce. If you cook broccoli in a microwave, some glucosinolates will leach into the water, so save the water and you can still get the benefits.
What about Stir-Frying?
Who doesn’t enjoy a tasty stir-fry? Unfortunately, it might not be the best cooking method for preserving nutrients. One study found that stir-frying led to the loss of vitamin C, carotenoids (anti-inflammatory nutrients and precursors to vitamin A), and chlorophyll. It also led to a loss of glucosinolates in broccoli.
Here are some general guidelines for cooking vegetables to retain nutrients:
- Cook for the shortest time possible.
- Use the least amount of water possible.
- Save the water and use it to make a sauce for the veggies.
- Don’t cut vegetables into small pieces before microwaving.
- Eat both raw and cooked vegetables to get the most nutritional benefits.
- Frozen veggies are a nutritious option too and they keep longer.
- Add a source of fat, like olive oil, to enhance absorption of water-soluble vitamins like beta-carotene.
- Choose vegetables in a variety of colors for a more diverse nutritional profile.
The Bottom Line
Boiling and stir-frying aren’t the best way to prepare vegetables. If you’re eating vegetables for their health benefits, steaming, and microwaving with a small amount of water is better. To further maximize the health benefits of veggies, add a healthy source of fat, like olive oil. Doing so will help you better absorb fat-soluble nutrients in vegetables, like beta-carotene. Enjoy your veggies and eat more of them!
References:
- “Vitamin C losses in some frozen vegetables due to various ….” 14 Dec. 2000, onlinelibrary.wiley.com/doi/abs/10.1002/1521-3803%2820001201%2944%3A6%3C451%3A%3AAID-FOOD451%3E3.0.CO%3B2-5.
- López-Berenguer C, Carvajal M, Moreno DA, García-Viguera C. Effects of microwave cooking conditions on bioactive compounds present in broccoli inflorescences. J Agric Food Chem. 2007 Nov 28;55(24):10001-7. doi: 10.1021/jf071680t. Epub 2007 Nov 3. PMID: 17979232.
- Jiménez-Monreal AM, García-Diz L, Martínez-Tomé M, Mariscal M, Murcia MA. Influence of cooking methods on antioxidant activity of vegetables. J Food Sci. 2009 Apr;74(3):H97-H103. doi: 10.1111/j.1750-3841.2009.01091.x. PMID: 19397724.
- Yuan GF, Sun B, Yuan J, Wang QM. Effects of different cooking methods on health-promoting compounds of broccoli. J Zhejiang Univ Sci B. 2009 Aug;10(8):580-8. doi: 10.1631/jzus.B0920051. PMID: 19650196; PMCID: PMC2722699.
- Dadali G, Ozbek B. Kinetic thermal degradation of vitamin C during microwave drying of okra and spinach. Int J Food Sci Nutr. 2009;60(1):21-31. doi: 10.1080/09637480701568038. PMID: 17886082.
- “Microwave cooking and nutrition – Harvard Health.” 17 Aug. 2021, .health.harvard.edu/staying-healthy/microwave-cooking-and-nutrition.
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