There’s no question that cooking can do wonderful things for the foods we eat—and no denying the fun of getting creative in the kitchen, for that matter. But you might not know that while the process of cooking can improve digestibility, add flavor, and in some cases, make food safer to eat, it can also have an impact on nutrient content.

Is that going to stop us from firing up the oven? Nope—we’ll always still recommend prioritizing your nutrient intake from your diet, and that means preparing your favorite nutritious meals in any way you see fit. But it also doesn’t hurt to practice a little curiosity around the nutritional value of your food and how different factors can have an impact, including cooking. So let’s take a closer look.

Cooking technique matters.

Remember the difference between water-soluble and fat-soluble vitamins? Here’s a quick refresher. Water-soluble vitamins (which include vitamin C, as well as B-vitamins like B12, folate, and riboflavin) are metabolized more quickly than fat-soluble vitamins (which include vitamin A, vitamin D, vitamin E, and vitamin K). That means we excrete any excess water-soluble vitamins when we urinate, while fat-soluble vitamins stick around longer in the body for later use.

Why does this matter? Because water-soluble vitamins tend to be more sensitive to heat, and they dissolve in water—which is why cooking method, time, and temperature can all have different impacts on nutrient composition. (1)

One 2018 study published in Food Science and Biotechnology observed different methods of cooking on the nutrient content of select vegetables. What they found was pretty telling: For example, microwaving seemed to retain the most vitamin C while boiling retained the least. Why? If you think about it, boiling involves cooking in a large amount of water—which can cause water-soluble vitamins to leach out. And since we don’t typically retain the water we cook our veggies in, that means some of that nutrient content can quite literally go down the drain. (2)

But when we’re steaming or microwaving, on the other hand, we’re often cooking for a shorter amount of time, and there’s minimal (if any) liquid involved—which might explain why there isn’t as much of an impact on nutrient content. Similarly, USDA data shows that when we use the liquid our vegetables are cooked in rather than dumping it, up to 15% more of vitamin C and folate are retained. Sauteeing and stir frying have also been linked with slightly better nutrient retention, since water isn’t usually used and the cooking time is shorter. (1,3)

Fat-soluble nutrients are sometimes enhanced by cooking methods, like stir-frying.

In the case of some fat-soluble compounds, some cooking methods can actually impact nutrient availability in a more positive way—especially if they involve a small amount of healthy fat. Beta-carotene, for example is a carotenoid: plant pigments that double as antioxidant.* Beta-carotene specifically gives carrots and sweet potatoes their orange hue, and also functions as a precursor to vitamin A. In one study that measured the impact of different cooking methods on carrots, for example, the researchers found that beta-carotene was easier to metabolize when carrots were stir fried in a small amount of oil, when compared their raw form. The reason for this can be traced to a couple of things. For one, the vegetable’s cell walls can be tricky for the human body to break down in uncooked form—but heat alters the wall structure, which is why cooking can ultimately make nutrients easier to metabolize. For another, beta-carotene is fat-soluble—which is why a small amount of oil can also have an impact. (2,4)

Another great example? Lycopene is related to beta-carotene in that it’s another fat-soluble carotenoid—giving tomatoes their rosy-red hue. One study found that when tomatoes were cooked in a small amount of oil, people were able to metabolize it slightly better than when they were cooked without oil—and even more so when compared to their raw form. (5)

The bottom line

Maybe stir-frying is already your go-to cooking method, and you love steaming your kale or broccoli. Maybe, on the other hand, you prefer raw carrots to sauteed, or your go-to mashed potato recipe requires boiling. Truthfully, while it’s nice to be mindful of the different things that can impact nutrition, we think the top priority is getting a wide array of veggies, fruits, and other nutrient-rich foods on your plate to begin with—prepared in the way that makes you most excited to eat them.

References:

1. Xu, F., Zheng, Y., Yang, Z., Cao, S., Shao, X., & Wang, H. (2014). Domestic cooking methods affect the nutritional quality of red cabbage. Food Chemistry, 161, 162–167. doi: 10.1016/j.foodchem.2014.04.025
2. Lee, S., Choi, Y., Jeong, H. S., Lee, J., & Sung, J. (2017). Effect of different cooking methods on the content of vitamins and true retention in selected vegetables. Food science and biotechnology, 27(2), 333–342. https://doi.org/10.1007/s10068-017-0281-1
3. USDA Table of Nutrient Retention Factors. (2007). Retrieved from USDA
4. Ghavami, A., Coward, W. A., & Bluck, L. J. C. (2011). The effect of food preparation on the bioavailability of carotenoids from carrots using intrinsic labelling. British Journal of Nutrition, 107(9), 1350–1366. doi: 10.1017/s000711451100451x
5. Fielding, Jeanette & Rowley, Kevin & Cooper, Pauline & Dea, Kerin. (2005). Increases...after consumption of tomatoes cooked with olive oil. Asia Pacific journal of clinical nutrition. 14. 131-6.