How do frozen vegetables compare to fresh ones nutritionally? Most of us assume that fresh veggies must be better for us, but the surprising answer is that sometimes frozen ones are the healthier choice.
When the vegetables were picked and how long ago are factors that make a difference for both fresh and frozen produce. Homegrown vegetables and those that are harvested for commercial freezing are usually picked when they are fully ripe, which is also when they are at their peak nutritionally. They are usually frozen soon after they are picked.
While each vegetable is still part of an actively growing plant, it continues to build its store of vitamins, minerals and phytonutrients.
If it is picked underripe, as is the norm for many commercially grown vegetables that are sold "fresh", it doesn't have as many nutrients as, for example, a tomato that fully ripened not only on the vine but on a vine that was still attached to a live root system.
That last bit is important. Sticking with the tomato example, there are "vine-ripened" tomatoes sold at the supermarket that were, indeed, ripened on their vines - after the vines had been severed from the parent plant. In other words, they were picked green and ripened on the vine but off the living plant, which means that their nutritional value (and taste, FYI) is not as good as that of field-ripened veggies.
A standard "fresh" supermarket vegetable was typically harvested underripe and then sat on a truck before sitting on a shelf before sitting in your refrigerator. After losing out on the chance to fulfill its nutritional potential because it was picked too early, it lost out even more in storage because the more ephemeral vitamins such as C and the B vitamin thiamin start to break down as soon as the plant is picked. If it takes as long as two weeks from when it is picked until you bite into it, as much as 50% of some nutrients will have been lost.
Many vegetables require a rapid blanching before freezing, and that process does destroy a small portion of the vitamin content. But so little is lost that frozen foods can contain significantly higher amounts of these vitamins than those tired specimens that were picked before their peak and stored for days or even weeks before you ate them.
Over time, the vitamin content of even frozen vegetables does decline, so it is important to pay attention to how long you can freeze each food.
The bottom line: If picked at their peak harvest time and eaten within a day or two, fresh or minimally cooked vegetables are usually more nutritious than frozen. However, compared to standard underripe supermarket vegetables from non-local farms, frozen veggies are often nutritionally superior. This means that in winter, if you live in a climate where the only "fresh" winter produce is storage crops or foods that traveled long distances to get to you, frozen vegetables are your healthier choice.
On a side but related note: Are home-frozen vegetables better for you than commercially frozen ones? Nutritionally, probably not. But home-frozen foods have an impressively smaller carbon footprint than that of their commercial cousins. If you keep your foods in reusable freezer containers, over time that adds up to an environmentally friendlier choice than disposable packaging that goes straight into the trash. And if your vegetables were sourced in your own backyard or from a local farmer, that is a vast reduction in the amount of fossil fuel that was burned to get them to you.