Certain cooking methods for some vegetables cause less nutrients to be digested because of the characteristics of vitamins and minerals and how they can be affected by heat and water (Spritzler, 2019).
The referenced Healthline article by F. Spritzler is linked at the bottom of the page, and that article (at the end of it) has a helpful list of 10 easy ways to preserve the nutrients in your food when you cook.
Here’s a list of some cooking methods and their effects on nutrients summarized from Spritzler’s article. You’ll notice that, in general, the best way to preserve the nutrients in vegetables is to cook for a shorter duration of time and use less water.
Vitamin C is water soluble and sensitive to heat, so when vegetables are boiled Vitamin C can be lost in significant quantities. Broccoli, spinach, and lettuce may lose up to 50% or more of their Vitamin C if boiled.
Vitamin B amounts decrease after exposure to heat because it is in the nutrient rich-juices that run off. In vegetables like peas, up to 60% of thiamin may be lost while the food is simmered and the juices run off. If the runoff juices are consumed then 100% of the minerals and 70-90% of B vitamins are digested. When grilling and broiling a significant amount of Vitamin B is lost because it is in the juice that drips from the vegetables.
Stir Fry and Sautéing:
More vitamins and minerals are retained when cooked by way of sauteing or stir fry’s than water based cooking methods. The shorter the duration of cooking time the more nutrients are preserved.
An important note, contrary to the loss of nutrients theme, is that when healthy fats are among the stir fry or saute mix, absorption of plant compounds and antioxidants can increase. For example, the absorption of beta carotene can be up to 6.5 times greater in stir fried carrots than raw carrots.
Vitamin C is lost in the instance of stir fries and sauteed dishes because of the exposure
to heat. The loss is less significant in the vegetables compared to other cooking methods that use water.
Roasting and Baking:
Because this is a dry heat there is minimal nutrient loss, unless the cooking duration is extensive. Vitamin B is most notably affected, but it is quite notable because it can decrease by 40% when exposed to high heats for too long.
Vitamin C is most significantly affected by the heat in microwaves, but because it is a dry heat, not too much is lost. Mainly green vegetables are affected and only about 20-30% of Vitamin C is lost.
Cooking vegetables by steaming them is the best way to preserve their nutrients. Broccoli, spinach, and lettuce have been shown to only lose 9-15% of their Vitamin C content.
Thank you for reading! - Elizabeth Beattie
Article for reference and more information:
Spritzler, F. (November 7, 2019). How Cooking Affects the Nutrient Content of Foods. Healthline. https://www.healthline.com/nutrition/cooking-nutrient-content