Delia Smith's current TV series and her new book How to Cheat at Cooking have caused a stir in Middle England. It seems that while we are perfectly comfortable with reaching for a can of tomatoes and red kidney beans to make a wholesome chilli con carne, many of us throw our hands up in horror at the thought of using tinned mince to rustle up a quick spaghetti Bolognese, feeling that this is a cheat too far.

With interest in farmers' markets at an all- time high, and organic vegetables being delivered to our doors, it is hardly surprising that Delia's new tack, which involves making use of everything from pre-roasted peppers to frozen roast potatoes, has caused a bit of hoo-haa. But do we have a right to dismiss shortcuts that could allow busy people to make tasty meals more easily? I don't think so and I feel strongly that we should not hide behind health issues when turning our noses up at such “cheats”.

“It looked like she was making dinner for my dog,” said a friend who watched Delia using canned meat on TV. “And it can't possibly be good for you” she added, feeling that, as a nutritionist, I'd have to agree.

In fact, I don't agree. Good-quality canned meats are as rich in protein as fresh versions and retain all-important iron, a mineral needed to keep our energy levels up and our stress levels down. They may not taste the same, and the means of production might make the animal welfare lobby turn the wrong sort of green - according to the RSPCA, as a rule of thumb, the more processed a food the less traceable it tends to be, and the less likely it is to be raised in a high-welfare system - but you can't condemn canned meat on nutritional grounds.

I think many of us have a slightly contradictory attitude to convenience foods. Why does canned mince cause such a reaction among many cooks who wouldn't bat an eyelid over cans of tuna used to knock up a quick salad Niçoise? Equally, why do we dislike the idea of frozen, pre-grilled slices of aubergine to make a moussaka and yet happily throw a handful of frozen peas into a risotto? Where you draw the line for including convenience ingredients in your cooking is a matter of personal choice. If you are a committed cook then, clearly, short- cuts will not be on your agenda. For others, who really do not have the time or perhaps the confidence to knock up 100 per cent home-made fare every night, maybe there is a place for dipping into a packet of frozen mashed potato or a jar of ready-fried onions to make life easier.

Take a look at the nutritional facts. Convenience does not necessarily mean forfeiting health. By understanding the processes involved in food preservation, you may come to see that the odd can of carrots, far from being a poor relation, can be a health booster.

FREEZING

What happens? Rapid freezing techniques convert water in the food into the smallest possible ice crystals. This means the water is not available to micro-organisms such as bacteria that spoil food, and the low temperatures slow down the rate at which bacteria can multiply. Rapid freezing techniques help to reduce damage to the texture and flavour of the food so that artificial additives such as colours, flavours and preservatives are not needed.

Does it affect nutrients? Nutrients are not seriously affected by the freezing process.

Great for peas and berries. In well-known brands, peas, for instance, are frozen within two-and-a-half hours of harvesting and the levels of vitamin C and B are often higher than in fresh foods which lose these nutrients during transportation and storage within shops and in the kitchen. Frozen mashed potato is also surprisingly good for vitamin C.

Be wary of Some immersion freezing techniques, especially for fish and prawns involves the use of brine which can increase salt content.

Golden rules Get frozen foods from the supermarket freezer into your own freezer as quickly as possible, ideally using a cold bag to transport them. As foods gradually defrost the vitamin C will start to decline. Also keep a temperature probe in your freezer and ensure that it remains under -18C.

CANNING

What happens? Food is cleaned and prepared, and then the cans are filled with a weighed amount of the food. Vegetables and fruits then have liquor (usually brine or syrup) added to fill the cans, which are then usually exposed to hot water or steam, heating contents to 95C. Lids are sealed on and the can is sterilised, usually by heating to about 121C for several minutes to kill bacteria. The cans are then cooled.

Does it affect the nutrients? Levels of heat-sensitive nutrients such as vitamin C are reduced through canning. While a 100g fresh peach has 31mg of vitamin C, 100g of canned peach slices has only 6mg. But supernutrients such as beta-carotene, the orange pigment in carrots, and lycopene, the red pigment in tomatoes, becomes easier for your body to absorb through the heating process, making canned versions a better source of nutrients than fresh versions eaten raw.

Great for tomatoes, carrots and spinach. Spinach contains the yellow pigment lutein, useful for warding off wrinkles and preventing age-related blindness, and canning makes it easier to absorb this. Canned fish such as mackerel, sardines and pilchards are also good for you. Canning helps to soften the bones in sardines and anchovies, making the bones edible and a great source of bone-building calcium. A 100g serving of canned sardines eaten with their bones gives you 500mg of the 700mg of calcium that we need daily. Canned pulses, such as kidney beans, are good for protein.

Be wary of canned tuna and vegetables. Tuna contains fewer omega-3 oils than other oily fish. The canning process damages these essential fats so that canned tuna is almost devoid of them. Vegetables canned in brine can contain about 1g of salt per 100g serving compared with zero in the fresh version, while fruit canned in syrup can contain 14g of sugar per 100g serving compared to 9.7g when canned in juice.

Golden rules Avoid any badly dented, bulging or rusty cans. The contents might have been spoilt and could cause serious food poisoning.

CHILLING

What happens? Foods such as ready-made cheese sauces, custard, pancakes and gnocchi are made and cooked as you would at home and then chilled within 30 minutes of cooking to 0C-3C. The chilled food must then be held at these temperatures when transported and when on supermarket shelves. They are then reheated for use at home.

Does it affect the nutrients? Nutrients such as vitamins C and the B group are lost, as they would be using cooking methods at home. Further losses, however, can occur during storage.Great for mainly milk-based sauces and custards, which are not greatly affected nutritionally because the minerals in them (calcium and magnesium, which are good for bones) are not damaged by cooking.

Be wary of chilled ready-to-use cheese and pesto sauces and ready-cooked crispy bacon are certainly convenient but can be high in fat, sugar and salt. Check label before tucking in.

Golden rules Check nutritional information before buying. A ready-made prawn cocktail may look appetising, but you can make a leaner version at home with low-fat mayonnaise.

BOTTLING

What happens? Pickling is a method of preserving food in which vegetables and fruits are preserved by covering them with vinegar, to which spices and sugar are sometimes added. Fruit can be bottled with sugar-rich syrups alone.

Does it affect the nutrients? Vegetables are often treated first with salt to extract some of their water and to prevent the growth of bacteria and so, nutritionally, pickled vegetables can be higher in salt than fresh veg. Fruit is cooked gently before pickling and therefore heat-sensitive nutrients such as vitamin C are damaged.

Great for red cabbage and beetroot. Both are rich in red and purple pigments (anthocyanins in red cabbage and betacyanins in beetroot), which have potential health-protecting roles in our bodies. Adding foods in vinegar to a meal slows stomach-emptying and lowers its glycaemic value so that you feel fuller for longer.

Be wary of Check the salt levels on the nutrition label. Pickles can also have quite large amounts of sugar added. For example, there can be four-and-a-half teaspoons in a serving of pickle with a ploughman's lunch. If you order a ploughman's, try to eat pickle in moderation.

Golden rules When buying healthy-looking bottled fruit compote, be aware that it is packed with sugar. Stewing your own fruit does not take long and you can use granulated fruit sugar (fructose), which has a lower glycaemic index value than sugar.

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