Vegetables are an essential part of our diet because they supply the body with carbohydrates which are our basic energy nutrient. In addition, vegetables supply essential vitamins, minerals and bulk. A daily fiber consumption of around three quarters of an ounce should be aimed for.
But nutrients are mainly concentrated in the outer layers of plants, so that too much trimming can result in nutrient loss. This is exacerbated during handling and preparation but can be lessened by following a few basic rules.
The preparation of vegetables can particularly affect the vitamin C content, especially if mincing and storage occurs. Simple cutting appears to have little effect on nutrient losses, but soaking and/or washing can increase nutrient loss due to the larger surface areas exposed to water.
To minimize loss wash fruit and vegetables before chopping or slicing, minimize chopping and cutting, and avoid mincing if possible. The biggest loss in nutrients, up to 50%, comes from heating and cooking. Vitamin C is particularly unstable under heating in most foods and losses of thiamin, riboflavin, carotene and niacin can also occur under certain conditions.
Boiling results in a significant loss of nutrients unless the cooking water is used for base stock or gravy, in which case the value is maintained. Steaming results in a greater retention of nutrients and again fluid can be re-used. Pan-frying or stir-frying can reduce the nutrient loss but the food should be cooked at low temperatures and for only short periods.
In summary, to minimize nutrient losses in vegetables this is what you should do. Store food for the shortest possible time, choose food that looks in good condition, and make chopping and cutting time as short as possible. Retain the outer layers of vegetables. Re-use cooking water for stock or soup, and serve food right after cooking. Cooked food should not be left and then re-heated and refrigerated food that has thawed out should not be re-frozen.