Cooking Vegetables & Vitamin Content - Ask a Nutritionist

July 27, 2023

What happens to the vitamins in a vegetable when you cook it? Are they destroyed? Where do they go? Tune into this week's episode of Ask a Nutritionist with Leah to get all these answers and more.

Join our Dishing Up Nutrition Facebook Community!


Podcast Powered by Podbean

Print Transcript


Welcome to the “Ask a Nutritionist” podcast, brought to you by Nutritional Weight and Wellness. We are thrilled to have you join us today as we discuss the connection between what you eat and how you feel, and share practical real life solutions for healthier living through balanced nutrition. Now let's get started.

LEAH: Hello and welcome to Dishing Up Nutrition's midweek segment called “Ask a Nutritionist”. My name is Leah Kleinschrodt. I'm a Registered and Licensed Dietitian with Nutritional Weight and Wellness. And on today's show I'll be answering a few related nutrition questions about one particular topic that we received from our Dishing Up Nutrition listeners.

So this particular listener says, “I recently read that cooking vegetables reduces or destroys vitamin content by as much as 50%”. So this person asked number one, is that true? And number two, are the vitamins leached into the water? So this is true when boiling vegetables or does heat of any kind denature the vitamins so there would be vitamin loss, no matter the cooking method, whether it's steaming, grilling, sauteing?

So there's a couple of parts to this question. It, these are really great questions. I love this. So to address that first question, is that accurate? I would say yes, no, and it depends. So super specific answer I know. I'm sure people love that answer, but we're going to, we're going to dive into this a little deeper.

The thing is, when we cook foods, there is a trade-off. So when we heat and cook food, yes there is going to be some nutrient loss or nutrients that are wasted no matter what, no matter the cooking method. But on the flip side, there are other nutrients in food that are actually enhanced or they're made more available to the body when we cook our food. Before I forget too, let's not forget that when we cook our food, there is a safety consideration also. So we lessen the risk of foodborne pathogens making it into our body. And that's always a plus. I think anybody who's ever been a victim of food poisoning will agree that that is not one way to retain nutrients in our body. So when we cook foods, there is that safety consideration in addition to what are we getting in terms of nutrient content out of our food.

Cooking food makes it more easily digestible

So when we think about cooking food in general, cooking makes food more easily digestible. So I mean, and the way I explain it to clients is in a sense, cooking predigests our food for us because it starts to break down some of the bigger structures in food like proteins or some of the fibers or some of like the cell walls that are in our plant foods.

And when we are able to do that, not within our own bodies, but outside our bodies to begin with, we're able to extract more energy and more nutrients out of that food. And so this is actually how historians and researchers think that humans really had some great leaps in our development and and becoming more human. And how we grew such big brains as we at some point in history learned how to harness, how to make fire and harness the power of fire.

So then we started cooking the animals that we hunted and the plants that we gathered, and that then we were able to get more nutrients out of our food by doing this with less effort than it was before. So it just meant a huge leap in development for our early ancestors; just a couple little tidbits historically about how that, how that came about.

So when we think about nutrients that are lost or they're degraded when we cook our foods, especially thinking about vegetables, 'cause this particular question was about vegetables. The big ones that we think about are vitamin C and a lot of the B vitamins. We also think about some of the polyphenols, which are just plant compounds that have some antioxidant properties to them.

Boiling vs. steaming vegetables

So there is research there that says yes, boiling vegetables, for example, can lead to as much as a 40 to 55% loss of vitamin C compared to steaming vegetables may only cause a loss of eight to maybe 15% or so of that vitamin C loss. And the B vitamins are thought to be similar. And this makes sense because both vitamin C and all of our B vitamins are water soluble vitamins, which means they get absorbed by water and then they follow water where it goes. So when we say boil vegetables and we heat up those vegetables, that vitamin C and those B vitamins are going to go where most of the water is, which is outside of the vegetables.

And this may not be a big deal if we're going to then consume that cooking liquid. So if you think about soups or stews where we are kind of boiling those foods, but we're usually going to eat the broth or the liquid that goes along with that, then we're still probably getting a fair amount of that vitamin C and those B vitamins and some of those polyphenols.

But say if we boil our vegetables and then we dump that water out and dump it down the drain, yes, we are going to lose, you know, possibly a fair share of some of that vitamin C and those B vitamins. So that does make the case for in general, when it comes to vegetables at least that cooking methods that use less water; so think roasting in the oven, steaming or stir frying; some of those types of methods; that will help reduce the loss of some of those particular vitamins.

Now I mentioned before, on the other hand, when we heat up vegetables, and again, this could be whether it's boiling or roasting, grilling, steaming, stir frying, anything like that, we actually make other nutrients more bioavailable and easier to absorb for our bodies. So this is because heat, as I mentioned before, kind of starts that breakdown process of the cell walls in that vegetable and the heat and the cooking starts to deactivate some of the components in plants that prevent us from being able to absorb some of our nutrients and some of our minerals.

So some people may have heard of phytic acid. Again, this is a naturally occurring plant compound, but it binds up to some of those minerals really tightly. So unless we do something to reduce the phytic acid, so again, cooking our food or soaking or sprouting and things like that, that phytic acid will not allow us to get access to some of those minerals. So this tends to be, again, like more of the case for minerals. So think zinc, iron, magnesium, potassium, calcium, a whole host of other minerals in there.

Cooking vegetables increases antioxidants

So cooking, heating our vegetables and starting that digestion process actually will help make some of those minerals more bioavailable. So just more easily accessed and absorbed by our bodies. And heat also tends to increase antioxidants in food. So think lycopene, like most people have heard of lycopene in tomatoes. It's kind of what contributes to some of that red color; carotenoids in carrots. These are our examples of some of those antioxidants.

And so we increase the amount and the bioavailability of those antioxidants when we heat and cook those foods. And those antioxidants are so important for fighting inflammation and for cancer prevention and for our immune system to be tuned up and ready. And so many other things.

As I mentioned before, again, think trade-offs. Yes, we may be losing some specific nutrients in the process of heating and cooking our foods and cooking our vegetables, but we also are likely increasing the availability of some other nutrients in our food.

Adding healthy fats to vegetables increases absorption of nutrients & antioxidants

And let's not forget. We've talked about this before on Dishing Up Nutrition, but adding healthy fats. So whether that is during the cooking process or after our vegetables have been cooked, adding healthy fats like butter, olive oil, avocado oil, avocados, I mean all sorts of healthy fats, will help with the absorption of many nutrients and antioxidants as well. So again, don't hesitate to use some of those good healthy fats somewhere along the line in that cooking process.


So yes, to summarize, yes, cooking vegetables, any method is going to lead to some loss of those nutrients. We think about it more for vitamin C and some of the B vitamins, but it makes some other nutrients more bioavailable. We can make the case that, you know, boiling vegetables, maybe that should be saved for if we're doing something more like soups and stews and something that is a higher liquid content.

And that when it comes to vegetables, using dryer methods of cooking will help preserve the most nutrients out of those foods. And just to throw it in there too, there are benefits to having some raw vegetables in the mixture. I know we didn't necessarily, that wasn't part of the question, but raw vegetables have their benefits also, again, just because sometimes we lose certain compounds, certain enzymes, certain nutrients when we cook our foods. So getting a nice balance of having some cooked foods and some raw foods in there, you're going to get really a whole plethora of benefits just by kind of having a mixture of those things in there.

So hopefully that answers that question and just kind of clarifies some of what that reader had or what that listener had read. So I want to thank you all so much for listening to Dishing Up Nutrition’s “Ask a Nutritionist”, and just know if you have a nutrition question that you would like us to answer, we invite you to join our Dishing Up Nutrition Facebook community by searching Dishing Up Nutrition on Facebook.

Join Our Dishing Up Nutrition Facebook Group

This is a private group. It is moderated by Nutritional Weight and Wellness nutritionists and nutrition educators, and it provides our community with a safe and supportive place to ask questions, share ideas, and just get inspired. And once you're a member of the community, we invite you to join the conversation and don't be shy to ask questions if you have one or if you have many, let us know. We look forward to hearing from you.

Print Transcript

Back To Top