Preparation is Key

Some vegetables are known for their sources of vitamins and antioxidants. We learned from a pool of nutritionists in South America that the way we prepare vegetables may impact their nutritional values. Here are few examples:

Carrot:
Rich in vitamins A, C and betacarotene. Also a source of sodium, potassium and carbohydrates.
Cooking it in water can cause the loss of 10 to 50% of vitamin C. Minimize it by cooking carrots in large chunks, little water and low heat or steam.
Roasting it in the oven may reduce its levels of minerals.
Warming up in the microwave may reduce the levels of vitamins.
Freezing it doesn't result in significant loss of nutrients.

Eggplant:
Rich in proteins, calcium and vitamins B1, B2 and C.
Cooking it in water and high heat can cause the loss of up to 50% of vitamin C, and 25% of vitamin B.
Roasting it in the oven may slightly reduce its levels of minerals.
Warming up in the microwave may slightly reduce the levels of vitamins.
Freezing it doesn't result in significant loss of nutrients.

Tomato:
Rich in lycopene, potassium, sodium, calcium, magnesium, iron, fibers, vitamin C and betacarotene.
Cooking it in water can cause the loss of vitamin C. Adding some oil increases the absorption of lycopene.
Roasting it in the oven with oil increases the lycopene absorption.
Warming up in the microwave reduces levels of lycopene.
Freezing it doesn't result in significant loss of nutrients.

Broccoli:
Rich in vitamins A, B, C and antioxidants. Also a source of calcium, iron, zinc, folic acid and potassium.
Cooking it in water can cause the loss of several vitamins. Minimize it by steaming instead.
Roasting it may reduce its levels of minerals, however increases the absorption of vitamin A.
Warming up in the microwave is a good way to keep its nutrients.
Freezing it doesn't result in significant loss of nutrients.

source: veja.com.br