"Eat fresh vegetables" used to be the motto for healthy eating. But with little time for food preparation and no time for daily shopping, I'm often asked if frozen vegetables can take the place of fresh. And if you live some distance from a good shopping centre, it's a fair question. So let's weigh up the odds ...

What does “fresh” really mean?

Firstly, you have to ask yourself just how “fresh” your fresh veggies really are? These days, “fresh” no longer means “just picked”. If your fresh vegetables have been sitting at the markets, then at the greengrocer or the supermarket and then in your fridge before you prepare them, their vitamin levels will have already declined significantly.

How you cook your veggies really matters

If you overcook your veggies or hold them warm for more than 5 minutes, that destroys some more (but not all) of the nutrients. What are lost are the heat-sensitive vitamins – vitamin C and two key B vitamins, thiamin (B1) and folate. The content of minerals (like potassium and magnesium) and fibre are unaffected by cooking.

Eat some raw veggies for a healthy boost

On the other hand, uncooked fresh vegetables – like a salad – give us a higher intake of these sensitive vitamins plus a number of antioxidants. I often recommend a salad a day for just this reason.

If raw is so good, why cook at all?

Cooking vegetables makes certain nutrients more biologically available to the body – for example, beta-carotene (converted into vitamin A in the body) and the antioxidant lycopene are absorbed better from cooked carrots or tomatoes than from raw. And if you add a splash of olive oil during the cooking, the fat further improves their bio-availability.

A healthy balance of cooked and raw veggies is the key

I suggest you eat a combination of both raw and cooked vegetables so that you can take advantage of what both have to offer. A salad at lunch and cooked vegetables at dinner is one way to do this.

Where do frozen veggies fit in?

Frozen vegetables can be as nutritious as home-cooked – as long as you cook them quickly in as little water as possible. Freezing (at -18°C for no more than 6 months) is the most nutritious and efficient way to preserve food.

Freezing is better than canning, as frozen vegetables retain a lot more of the heat-sensitive nutrients (particularly vitamin C, thiamin and folate) and have a better texture. Yes frozen veges lose SOME of these vitamins but not all. Also there’s little additional salt which is a big drawback with canned vegetables. 

The bottom line for healthy vegetable cooking

• The golden rule for all veggies is to cook until just tender but still crisp.
• Don’t keep them warm for long periods before you serve them.
• Use as little water as possible. Steaming, microwaving or baking are best.
• With frozen vegetables, remember they’re already half cooked, so they need only a final heat. Think a minute in rapidly-boiling water tops.
• If you microwave, then your vegetables don’t even need any water.