How do I boil/cook frozen vegetables to maintain nutrients?

What you want to avoid is where you leave lots of liquid behind.

When you're boiling, water soluble nutrients (eg minerals, vitamins B) will be leached out.

If you cook it slowly in fat (oil, butter, etc.), but it's so much that it's a puddle left behind, you might be losing fat soluble vitamins (eg, vitamins A, D, E)

Cooking at too high of a heat can also break down nutrients into other compounds ... but it's a trade-off, as cooking breaks down cell walls and makes them more bio-available.

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Personally, I tend to look at flavor, not just nutrients, as if it doesn't taste good, you're not going to eat it, and then you won't get any nutrients.

So, I'd recommend a 'steam-sauté' method:

• Put the vegetables in a pan with a little bit of water (about 3 TB / 45mL) and a lid
• Heat until you have steam, and let steam for a couple of minutes (exact time depends on the size of what you're re-heating, but you want them defrosted)
• Take the lid off, and let most of the water evaporate. You can push the veg to one side to speed this up
• Add a little oil and whatever seasoning, and cook 'til you get a little bit of color

For fresh vegetables, I'll sauté first, then steam. (and for brocolli, I saute the sliced up stems before adding the florets)

Use a microwave. Microwaves have been shown to preserve more nutritional value in vegetables than boiling in numerous studies. When it comes to maximizing the amount of nutrients retained in vegetables a microwave literally cannot be beat. A few studies have found that microwaving certain vegetables actually makes certain nutrients more available too so depending on the vegetable microwaving might actually be more nutritious than eating it raw.

If you don't want to use a microwave then you need to blanch them. I defrost mine on the counter, but if you're using enough water then you shouldn't need to worry about the temperature drop too much. Experiment and use common sense when adding frozen stuff to hot water.

Now, with the above out of the way, if you're eating enough vegetables it doesn't matter how you boil them when it comes to the micro-nutrients. The simple fact of the matter is that vegetables don't just contain nutrients, they're loaded, absolutely strapped, with them. If you actually eat enough vegetables - with a good amount of variety of course - you should really be getting all of the nutrients you need that you could get from eating vegetables regardless of the amount of nutrition lost to boiling. Cooking method isn't going to make a ton of difference, unless you boil them for 4 hours or something, but even with that if you just eat a few servings of vegetables that aren't cooked to death you should be fine. Keep in mind that adding a ton of fat or sugar to vegetables is going to affect your macro-nutrients(Macro-nutrients are protien, carbs, and fat, Micro-nutrients are vitamins and minerals and stuff)

One thing that's important to note is that you probably don't get all of the nutrients you actually need from vegetables. Most Americans don't get enough b12 so you should be taking b12 supplements.(The rate of b12 deficiency in omnivores is high enough to suggest that the average american isn't getting enough b12 from meat either so you should really be eating b12 fortified foods or taking supplements anyway.)

Before the argument starts, frozen vegetables lose less nutrients over time than "fresh" vegetables do. If you're not growing your own food, frozen vegetables are the most nutritional choice.

sous vide, although cumbersome, is likely best. No water Comes into contact with the vegetables, and this minimizes loss of nutrients. You can also precisely determine the temperature for the vegetables which can minimize loss of water and nutrients.

It depends on vegetable in question.

I generally use the steam of the boiling water to defrost green beans; then boil them directly in the same water for a couple of minutes.

You can also add a small amount of butter and a bit water and slowly cook them in a pot directly frozen. I use this method for frozen green peas, when I want to make a green pea mash.

actually, most people are surprised that boiling is the best method of cooking to maintain the most nutrients in vegetable products after that comes microwaving, then steaming, baking is one of the worst, and then frying and smoking/grilling which both have a number of unhealthy characteristics from these methods.

First. To freeze any veg you must blanch it. That mean what you have bought frozen, is already cooked. Defrost in the microwave end of story.