Most people know that boiling vegetables to death is generally not best for them, but raw isn’t always best either, and if we want to not sabotage our food, then there’s more to bear in mind than “just steam them, then”.

So, what should we keep in mind?

Water solubility

Many nutrients are water-soluble, including vitamin C, vitamin B-complex (as in, the collection of B-vitamins), and flavonoids, as well as many other polyphenols.

This means that if you cook your vegetables (which includes beans, lentils, etc) in water, a lot of the nutrients will go into the water, and be lost if you then drain that.

There are, thus, options;

• Steaming, yes
• Use just enough water to slow-cook or pressure-cook things that are suitable for slow-cooking, or pressure-cooking such as those beans and lentils. That way, when it’s done, there’s no excess water to drain, and all the nutrients are still in situ.
• Use as much water as you like, but then keep the excess water to make a soup, sauce, or broth.
• Use a cooking method other than water, where appropriate. For example, roasting peppers is a much better idea than roasting dried pulses.
• Consume raw, where appropriate.

Fat solubility

Many nutrients are fat-soluble, including vitamins A, D, E, and K, as well as a lot of carotenoids (including heavy-hitters lycopene and β-carotene) and many other polyphenols.

We’re now going to offer almost the opposite advice to that we had about water solubility. This is because unless they are dried, vegetables already contain water, whereas many contain only trace amounts of fat. Consequently, the advice this time is to add fat.

There are options:

• Cook with a modest amount of your favorite healthy cooking oil (our general go-to is extra-virgin olive oil, but avocado oil is great especially for higher temperature cooking, and an argument can be made for coconut oil sometimes)
• Remember that this goes for roasting, too. Brush those vegetables with a touch of olive oil, and not only will they be delicious, they’ll be more nutritious, too.
• Drizzle some the the above, if you’re serving things raw and it’s appropriate. This goes also for things like salads, so dress them!
• Enjoy your vegetables alongside healthy fatty foods such as nuts and seeds (or fatty animal products, if you eat those; fatty fish is a fine option here, in moderation, as are eggs, or fermented dairy products).

For a deeper understanding: Can Saturated Fats Be Healthy?

Do not, however, deep-fry your foods unless it’s really necessary and then only for an occasional indulgence that you simply accept will be unhealthy. Not only is deep-frying terrible for the health in a host of ways (ranging from an excess of oil in the resultant food, to acrylamide, to creating Advanced Glycation End-products*), but also those fat-soluble nutrients? Guess where they’ll go. And unlike with the excess vegetable-cooking water that you can turn into soup or whatever, we obviously can’t recommend doing that with deep-fryer oil.

*see also: Are You Eating AGEs?

Temperature sensitivity

Many nutrients are sensitive to temperature, including vitamin C (breaks down when exposed to high temperatures) and carotenoids (are released when exposed to higher temperatures). Another special case is ergothioneine, “the longevity vitamin” that’s not a vitamin, found in mushrooms, which is also much more bioavailable when cooked.

So, if you’re eating something for vitamin C, then raw is best if that’s a reasonable option.

And if it’s not a reasonable option? Well, then you can either a) just cope with the fact it’s going to have less vitamin C in it, or b) cook it as gently and briefly as reasonably possible.

On the other hand, if you’re eating something for carotenoids (especially including lycopene and β-carotene), or ergothioneine, then cooked is best.

Additionally, if your food is high in oxalates (such as spinach), and you don’t want it to be (for example because you have kidney problems, which oxalates can exacerbate, or would like to get more calcium out of the spinach and into your body, which which oxalic acid would inhibit), then cooked is best, as it breaks down the oxalates.

Same goes for phytates, another “anti-nutrient” found in some whole grains (such as rice and wheat); cooking breaks it down, therefore cooked is best.

This latter is not, however, applicable in the case of brown rice protein powder, for those who enjoy that—because phytates aren’t found in the part of the rice that’s extracted to make that.

And as for brown rice itself? Does contain phytates… Which can be reduced by soaking and heating, preferably both, to the point that the nutritional value is better than it would have been had there not been phytic acid present in the first place; in other words: cooked is best.

You may be wondering: “who is eating rice raw?” and the answer is: people using rice flour.

See: Brown Rice Protein: Strengths & Weaknesses

Want to know more?

Here’s a great rundown from Dr. Rosalind Gibson, Dr. Leah Perlas, and Dr. Christine Hotz:

Improving the bioavailability of nutrients in plant foods at the household level

Enjoy!