People always seem to think that food out of a freezer isn’t any good when it comes to nutrition, but that’s something I want to clear up, as frozen veggies (and fruit) are such a quick win when it comes to cooking healthy meals.
The nutritional content of all produce will depend on a number of factors including the soil, weather, season, farming methods, storage duration, conditions, and will ultimately be determined by if/how it's cooked (avoid boiling in favour of steaming/grilling to retain the maximum amount of nutrients).
FRESH produce can be ripened on the vine or in transit. Most produce absorbs nutrients from soil during its early growth, so this is not an important factor for nutritional content in terms of deciding if one is better than the other.
FROZEN produce undergoes minimal processing at source and therefore has very similar overall nutritional content to fresh veggies. If the produce is blanched before being frozen, there may be some nutrient loss, but this is minimal. The main thing that blanching does is affect the flavour (I mean, a frozen tomato is NEVER going to taste as good as a fresh one, is it?).
CANNED produce undergoes more processing than frozen and some of the added preservatives/salt/sugar can break down nutrients. Additionally, some cans are lined with BPA, which nobody wants to be eating.
VERDICT: so on the whole, there isn’t really a significant difference between fresh or frozen veg, and even eating canned veg will give you some nutrients too.
Having a freezer full of frozen veggies is such an easy way to reach your 5 a day target, it’s cheaper and less hassle than fresh veg as it’s pre-chopped, and if you’re putting it into a curry or stir fry which is packed full of flavour then the slight loss of flavour won’t make any difference. Win win!
Another perk of frozen food is that the freezing process will more often than not kill any harmful pathogens that may be in or on the food, so the chances of your food going off, or even getting food poisoning, are much less. Fresh food (even when kept in a fridge) risks the growth of pathogenic and spoilage-causing food borne bacteria.
One of the main downsides of frozen produce is that it can sometimes suffer from freezer burn. This occurs when there is a loss of moisture on the food which causes that hard, grazed looking texture on food when it's defrosting. This part is harmless and can be cut off the food, although you can try and prevent it occurring in the first place by wrapping food tightly to limit air exposure and not leaving the produce in the freezer for too long.