Eating a balanced diet may seem like the most obvious way to get your vitamins and minerals, but are you getting the maximum nutritional value from your food?

Although Nigella Lawson, Gordon Ramsey and Jamie Oliver may beg to differ, the real reason we cook our food is to increase the digestibility and eating quality of raw fare. However, while it almost always improves the taste, cooking also results in many nutrients being lost in the process. So how can you optimise the nutrients in your food without compromising the flavour?

The most vulnerable nutrients in our foods are those that are water soluble - meaning those that can be dissolved in water - such as B group vitamins and vitamin C.

Vitamin C
Being water soluble, this vitamin is easily destroyed by heat or through extended exposure to air. This means that during both the preparation of vegetables and fruit - after they have been peeled or shredded - and cooking, vitamins are rapidly lost. The best way to maximise the vitamin C content is as follows:

• Prepare fruit and veggies just before you are going to use them.
• Use only a small amount of water when cooking and cook veggies for only a short period of time. This includes adding veggies to boiling rather than cold water to reduce their time spent in water.
• Don't add sodium bicarbonate to the cooking water in order to retain the green colour of veggies, as this will only speed up the rate at which vitamin C is lost. This is because the vitamin is unstable under an alkaline environment.
• Don't delay serving veggies once they're cooked, as the levels of vitamin C drop with time. For example, if cabbages are kept warm and left for half an hour before serving, 40% of the vitamin C is lost.
• The vitamin C content in fruit and vegetables decreases with storage. While you may not think that potatoes provide much vitamin C, because we tend to eat a lot of them they are actually a very useful source. Vitamin C levels are highest in new potatoes and freshly dug potatoes and fall gradually after harvesting and storage.
• Different methods of cooking potatoes will affect the vitamin C content. For example, if potatoes are peeled before they are boiled, between 20 to 50 per cent of vitamin C can be lost. This is because vitamin C is present just underneath the skin of potatoes. It's therefore best to either boil or bake potatoes with their skin intact.
• Freezing veggies and fruit as a way of prolonging their life won't result in large losses of vitamin C unless they have been blanched beforehand.

B group vitamins
Although all the B group vitamins are water soluble and easily destroyed by heat, thiamin, or vitamin B1, is the least stable of them all.

Thiamin leaches out easily into cooking water and is lost readily if cooked in the juices from meat. Like vitamin C, thiamin is unstable under alkaline conditions and so is also easily lost if sodium bicarbonate is added during cooking. Around 5 to 15 per cent of thiamin is lost from eggs if they are boiled, fried or poached.

Riboflavin, which is found in milk, is equally unstable and can be destroyed by light. It is therefore important not to leave bottles out on the doorstep exposed to sunlight for more than an hour, or else large losses can occur.

Meat, which is a good source of the B group vitamins, also loses nutrients when cooked, although different methods will affect the amount lost. Frying or grilling meat will lead to a loss of around 20 per cent, whereas stewing will lead to greater losses - between 20 to 70 per cent, depending on whether the juices are consumed, since most of the nutrients will have seeped into the juice.

B vitamins can also be lost while cooking fish - around 10 to 30 per cent are lost if fish is baked, fried or grilled.

Other vitamins and minerals
Generally, fat-soluble vitamins, such as vitamin A, D and E, are stable regardless of the cooking method used. Minerals are also unaffected by heat but can be lost in the cooking water when boiled or blanched or steamed.

Cooking tips
The best way to preserve all of the above vitamins when cooking meat, fish or eggs is to remember the following basic points:

• Boil or steam vegetables for a minimum length of time in a minimum amount of water.
• Boiling vegetables in the microwave is a useful way to minimise vitamin C losses, since this process heats them up rapidly and uses only a minimum amount of water.
• If not stored for long periods of time, fresh fruit and vegetables are the best sources of all water-soluble vitamins. However, there are large losses of vitamin C and folate in fruit and veggies that have been stored for long periods and are wilted.
• Don't throw away the cooking water, as you'll be throwing vitamins and minerals down the drain. Keep them to use for gravy.
• Keep the meat juices and use it as gravy as they also retain a large amount of vitamins and minerals. Remember to skim the fat off first.