Ever wonder how nutrient content varies between cooked and raw vegetables? Well, the short answer is that it’s good for us to eat a combination of raw and cooked vegetables. This is because the effects of cooking are different depending on the nutrient in question.
Cooking is a double edged sword because it modifies both the physical and chemical properties of foods which can cause leaching of certain nutrients and phytochemicals. But it can also be a great thing because it also softens cell walls which facilitates the extraction and absorption of others. Let’s take a look at some key things to remember.
While many nutrients can be damaged by heat, light, or oxygen, vitamin C looks to be the nutrient that is most vulnerable to cooking. In fact, about 30 percent of vitamin C in leafy greens can be destroyed by cooking. Other nutrients affected by heat are folate, other B vitamins, and some antioxidants. But, minerals and the fat-soluble vitamins, A, D, E, and K are much more stable when heated.
Cruciferous vegetables like kale and collard greens win the prize for their powerful anti-cancer properties. They contain valuable nutrients called glucosinolates, which are converted to cancer-fighting compounds when the plant cells are broken up by chopping or chewing. What’s important to know here is that heat inactivates the enzyme that makes this conversion happen, so a good thing to do is to chop or even blend these vegetables before cooking. In fact, blending the raw greens and then adding them to a soup of stew preserves the most anti-cancer properties. Try adding some raw kale or other leafy green to a smoothie for a serious nutritional boost! Steaming when compared to stir-frying, boiling and microwaving results in the smallest nutrient losses in broccoli. But the less it is cooked the better.
Carotenoids like alpha-carotene, beta-carotene, and lycopene are very heat stable and become even more absorbable once foods are cooked. This is why tomato sauce or paste is such a great source of lycopene. Carotenoids are located in the plant cells and some of that cellular structure must be disrupted by blending or heating to make them more available to the digestive system. Steamed carrots and beets anyone?
Did you know that there is some nutrient loss when fresh foods are stored? This is why produce that has been shipped a long distance will tend to have less nutritional value than if you bought the same produce locally. For me, “local” means that it’s grown within a 100-mile radius of where I live. This greatly expands what’s available and I have found many really cool veggies like different squashes that I have never tried before.
Frozen vegetables do have some nutrient loss due to the blanching step of the freezing process. But, once the food has been frozen, the nutrient loss slows down considerably. And because frozen vegetables are picked when they are fresh and frozen soon after, this preserves many of the nutrients. Frozen fruits do even better because they are not blanched before they are frozen.
Try to avoid high-heat dry cooking and browning like roasting to prevent the formation of acrylamide which is a possible carcinogen formed in cooked starchy foods. You know that gorgeous brown color on roasted potatoes? That indicates the presence of acrylamides! I know, I know, roasted potatoes taste amazing! So, just try not to have them very often.
The best way to maximize the amount of the nutrients you get is to eat a large variety of raw and gently cooked vegetables. Think large daily salads, vegetable-bean soups or stews, or even vegetables steamed for only 10 minutes. And when you have a large green salad be sure to add a sprinkle of raw, unsalted nuts or seeds like walnuts or flaxseed because they will help your body to absorb the carotenoids in the vegetables.
Here’s some tips to remember for healthy cooking methods for vegetables:
- Steam your greens in a steamer for 10 minutes or less
- Add sweet potatoes, carrots and parsnips to soups and stews
- Hard squashes are best baked at a low oven temperature (325° F) for 1 hour
- Steam mushrooms and use in a salad or add to soups and stews
- Puree raw cruciferous greens like kale along with shallots and onions before adding to soups and stews
To your good health!