Many people believe that frozen vegetables are less nutritious than fresh vegetables, since foods which have been processed are often less nutritious than ones that have not been. That said, it appears that frozen vegetables are at least as nutritious as fresh ones — and in some situations, they may actually be more nutritious.
Part of the confusion probably arises from the fact that vegetables lose much of their nutritional value when certain preparation techniques are used. Proponents of a raw food diet will discourse at length about the health benefits of eating vegetables that haven’t been heated past a certain temperature. Canned foods are often less nutritious than fresh, because they are cooked for a very long time, and then often packaged with a great deal of salt. Vegetables to be frozen, however, are not heated and so do not undergo the same denaturing of proteins or loss of vitamins in waste water.
The term “fresh vegetables” needs to be looked at a bit closer to determine whether frozen vegetables might actually even be more nutritious. Truly fresh vegetables, of course, are those that a person picks out of his own garden, or are perhaps purchased at a farmer’s market the day they’ve been harvested. These vegetables are ideally picked at the peak of their freshness, and if a cook prepares them that evening, they will be full of minerals and vitamins.
When most people talk about fresh vegetables, however, they mean vegetables purchased at their nearby supermarket, an aisle or two away from the frozen foods. These vegetables aren’t nearly as fresh as those from a person's own garden. In many cases, they’ve spent days or weeks in transit, and then some time in the produce aisle. Over that time, vitamins and minerals have leeched out, and by the time a cook buys and prepares them, they are often far from their peak ripeness.
Frozen vegetables have usually been picked at the peak of their ripeness and immediately flash frozen. As a result, all of the minerals and vitamins are locked in, ready for the consumer's benefit. This means that in some cases, these vegetables might be more nutritious than those purchased from the produce aisle that have been sitting for weeks. They may also have the outer cellulose layer already broken as a result of the freezing, making it easier for the body to digest them.
There are some things that may make frozen vegetables less nutritious than fresh, however. Shoppers should avoid products that have sugar or salt added — good ones should just have the vegetables listed in the ingredients. Also, cooks must take care that they don’t leech out the good nutrients by boiling the vegetables for a long time — the less produce is boiled, in general, the more vital ingredients it will retain.
When chosen thoughtfully, vegetables that have been flash frozen are no less nutritious than fresh. Of course, fresh vegetables usually have much richer flavors, and most people find the texture preferable. When these considerations don't bother the eater, however, and he prefers the convenience of frozen products, nutritional issues shouldn't be a concern.