The nutritional value of vegetables on your plate is not the same as the nutritional value of those vegetables in their raw state. Cooking can both enhance and reduce nutrient availability depending on the specific nutrient, the cooking method, and the cooking time. Understanding these relationships allows you to maximise the nutritional return from the food you buy.
Nutrients That Are Lost in Cooking
- Water-soluble vitamins including vitamin C and B vitamins: lost rapidly when boiling vegetables in water; steaming, roasting, or stir-frying preserves significantly more
- Myrosinase enzyme in cruciferous vegetables: destroyed by boiling before glucosinolate-to-sulforaphane conversion has occurred; chop and rest before cooking
- Probiotic bacteria in fermented foods: destroyed by heat above 40 degrees Celsius; do not cook kefir, live yoghurt, or raw sauerkraut
Nutrients That Are Enhanced by Cooking
- Lycopene from tomatoes: bioavailability increases substantially with cooking in the presence of fat; cooked tomatoes with olive oil are far superior to raw for lycopene absorption
- Beta-carotene from carrots and sweet potato: cell wall softening by cooking significantly increases carotenoid bioavailability
- Starch digestibility in legumes: raw legumes contain lectins and other antinutrients that are deactivated by proper cooking; soaking and thorough cooking is essential for safe and nutritious consumption of dried beans
Best Cooking Methods by Priority
For most vegetables: steaming preserves the most water-soluble vitamins. Roasting with extra-virgin olive oil enhances carotenoid absorption and produces flavour through Maillard reactions. Light stir-frying in a small amount of oil is fast and preserves most nutrients. Boiling is the least efficient method for nutrient preservation and the cooking water should be used in soups or sauces if the vegetables were boiled.