Keeping Food's Nutritional Value: Tips for Preserving Vitamins When Cooking Vegetables

Cook Vegetables without Losing Nutrients

Different cooking techniques make a tremendous difference in the retention of different nutrients in plant foods. Let's take a look at the results of different cooking methods in the nutritional content of broccoli.

Nutrients in Broccoli

Some people love its taste, and some people hate its taste, but every nutritional expert agrees that broccoli is one of the most nutritious of all plant foods. A single 3-1/2 oz (100 gram) serving of raw broccoli only sets you back 34 calories, but it provides thiamine (vitamin B1), riboflavin (vitamin B2), niacin (vitamin B3), pantothenic acid (vitamin B5), pyridoxine (vitamin B6), folic acid, vitamin C, vitamin E, vitamin K, lutein, zeaxanthin, beta-carotene, calcium, iron, magnesium, and fiber. It is also one of the best natural sources of a group of cancer-fighting compounds known as the glucosinolates.
 
A high intake of broccoli is known to reduce the risk of prostate cancer in men and the risk of heart disease in both sexes. The only downside to eating broccoli is that it is well known for causing malodorous flatulence, because of the high sulfur content of its cancer-fighting compounds.

Different methods of cooking broccoli have different effects on nutrient retention. There is no single best method of cooking that preserves all of its nutritional value.

Vitamin C in Cooked Broccoli

Scientists at Zhiejiang University in China measured vitamin C in broccoli after several different cooking methods. They found that:

• 33% of vitamin C was destroyed by boiling,
• 24% of vitamin C was destroyed by stir-frying,
• 18% of vitamin C was destroyed by microwaving, but
• Steaming broccoli caused no significant loss of vitamin C.

Heating broccoli does not destroy vitamin C, but contact with hot liquids seems to dissolve vitamin C.

READ The Top Eight Foods Rich in Vitamin C

Sugars in Cooked Broccoli

If you have ever eaten broccoli the same day it was harvested, you probably noticed that it is a naturally sweet vegetable. These sugars break down if broccoli is held in refrigerated storage for weeks or months before being sold as "fresh" broccoli in the market. Certain cooking methods preserve far more of these natural sugars than others.

• A 100 gram serving of raw broccoli contains about 4 grams of natural sugars.
• A 100 gram serving of steamed or microwaved broccoli contains about 3 grams of natural sugars.
• A 100 gram serving of boiled broccoli contains about 2 grams of natural sugars.
• A 100 gram of stir fried broccoli contains about 1 gram of natural sugars.

Many stir fry sauces include sugar to make up for the natural sweetness lost in frying the vegetable.

Glucosinolates in Cooked Broccoli

And what about the cancer-fighting compounds in cooked broccoli. What does cooking do to them?

• Boiling removed about 40% of the cancer-fighting compounds in broccoli.
• Stir-frying removed about 55% of the cancer-fighting compounds in broccoli.
• Steaming had no effect on the cancer-fighting compounds in this favorite vegetable.

For broccoli, steaming preserves the greatest nutritional content. But what about for other vegetables?
 

Special Benefits from Different Cooking Techniques

In the study of nutrient retention after cooking of broccoli, steaming was the clear winner. But not every food has to be steamed.
 

The Best Way to Boil Vegetables for Nutrient Retention

Heat water to boiling before adding vegetables. The less time it takes to cook your veggies, the fewer nutrients leach into the cooking water. When possible, peel vegetables such as beets and potatoes after they have been boiled.

The Best Way to Microwave Vegetables for Nutrient Retention

The enzymes in vegetables often survive microwaving at low power. For example, one study found that there is little enzyme loss in red cabbage cooked in the microwave for 24 minutes at 180 watts, but almost total loss of enzymes in red cabbage cooked in the microwave for 4 minutes at 900 watts.

The Best Way to Fry Vegetables for Nutrient Retention

If you must fry your vegetables, soak them in salt water for 2 hours in the refrigerator and then dry thoroughly before you cook them. They will have a more pleasing texture, and lose fewer nutrients.

READ How to Stop Eating Junk Food: Top Tips

The Best Way to Roast Vegetables for Nutrient Retention

Leave vegetables in their peels or rinds or coat them with olive oil before roasting or baking. Get flavor from salt, spices, and marinades rather than from the char on slightly burnt vegetables.

The Best Way to Steam Vegetables for Nutrient Retention

Make sure you are steaming your vegetables, not boiling them. Allowing water to boil up to the level of the steamer leaches out nutrients, and causes the vegetables to cook unevenly.

Here are some additional helpful hints for retaining nutrient content of cooked vegetables.

• Beans contain lectins that can trigger autoimmune reactions resulting in anemia in susceptible individuals. Never eat beans raw.
• Boiling helps release iron into a form that can be absorbed by the body, especially if the meal also includes a food rich in vitamin C. If you are eating a food for its vitamin C value, boil or stew it.
• Cooking beans and lentils in a pressure cooker converts their carbohydrates into a form that has minimal effect (but not no effect) on blood sugar levels after they are digested.
• French fries come with a warning label in some states and cities because the process of frying them produces acrylamides, a "potential carcinogenic material." A study of fried potatoes in Sweden, however, found that people who ate the most fried potatoes had the lowest levels of colon cancer.
• Simply putting a cover over a skillet used to fry food greatly reduces the production of toxic compounds.
• Adding MSG (monosodium glutamate) to foods makes many plant compounds more soluble and more likely to leach out into cooking water or frying oil.
• Broccoli that is stir-fried in virgin olive oil does not lose cancer-fighting glucosinolates.
• The use of tenderizers helps kill E. coli.
• Starchy vegetables lose almost all of their vitamin content during canning. Green, red, and yellow vegetables lose very little.
• Overheating any sauce can make it curdle—even in the microwave. Lower power in the microwave helps keep sauces tasty.
• Vitamin B12 is destroyed in the microwave. Either cooking or reheating food in a microwave destroys vitamin B12, converting it into an inactive form.