Healthy food preparation and cooking demands attention to detail, timing and patience. Retaining the maximum nutritional value, while also keeping the risk of bacterial contamination to a minimum are both important aspects ofpreparation. These principles should be kept in mind whatever type of food is being prepared, cooked, stored or reheated.
Foods such as meat, fish, fruit and vegetables need to be cleaned thoroughly before cooking and prepared with both hygiene and nutrition in mind. Partly defrosted and under-cooked food can lead to food poisoning – it is particularly important to bear this in mind when preparing meat and poultry. Harmful bacteria in food can be killed by high temperatures during cooking. Over-cooking, however, destroys precious nutrients. All cooking methods result in the loss of some nutrients, but these losses can be minimized by choosing methods that are both appropriate and healthy. Good hygiene is also important when cooling, storing and reheating cooked foods.
Before cooking, fresh foods should be thoroughly cleaned and trimmed of all inedible parts. Meat and poultry should be washed under cold running water and dried with kitchen paper. Particular care is needed in the preparation of poultry. Meat and poultry should be trimmed of excessive visible fat so that total fat content is reduced. Fresh fish should be gutted to remove the internal organs. Fish should also be washed under a running cold tap and dried with kitchen paper before cooking.
Fruit and vegetables must be washed thoroughly to remove soil, insects and pesticide residues. Delay washing, peeling and grating until just before eating or cooking so that the maximum amount of nutrients is preserved. Any rotting or mouldy produce must be discarded because it can contain toxins which may cause stomach upsets. Bruised fruits and green sprouting potatoes should be rejected for the same reason.
Vegetables and some processed foods can be safely cooked from frozen, but fish, meat and poultry must be thoroughly defrosted before cooking. If frozen meat and poultry are not thawed all the way through, they may not cook properly at the centre. Whenever possible, food should be defrosted in the refrigerator or by using a microwave. Defrosting at room temperature should be avoided because the warmth encourages growth of harmful bacteria. Poultry and game, in particular, should not be defrosted at room temperature.
By choosing an appropriate cooking method, it is possible to keep nutrient losses to a minimum, while ensuring that a healthy and hygienic meal is prepared. Cooking techniques include grilling, barbecuing, baking and roasting, stir-frying and steam-frying, shallow frying and deep-fat frying (which use a high heat and usually some fat, either already contained in the food, or added); and steaming, poaching, and boiling (which use varying amounts of water to cook foods). Microwaving cooks foods quickly using electromagnetic radiation.
Particular care should be taken when preparing and cooking foods for consumption by the very young, the elderly,and anyone who has a weakened immune system (such cancer or AIDS patients). These individuals are particularly vulnerable to food poisoning, so thorough cooking is essential.
Fish, tender cuts of meat and fatty meat products such as bacon, burgers and sausages can all be cooked by grilling. It is a healthier alternative to frying because much of the fat from the meat drips into the tray below. Any fat remaining on the food can be blotted off with kitchen paper. When grilling meat, however, it is advisable to avoid burning fat, as this generates undesirable free radicals.
Barbecue cooking can be used for meat, meat products such as sausages and burgers, fish and vegetables. Some experts believe that charred meat cooked on a barbecue may pose a health risk to humans, because the charring process produces chemical compounds that have been linked to cancer in laboratory animals. Fat dripping onto the coals or hot metal below the grill can also produce potentially cancer-causing agents called benzopyrenes. These substances vaporize, stick to the coal soot and deposit themselves on the meat. To prevent the problem of burning meat juices, cover the grill with aluminium foil before cooking; alternatively, wrap food in foil. With these precautions, outdoor cooking can be enjoyed without the potential health risks.
Baking and roasting
The oven is an ideal place to prepare many everyday foods, including meat, poultry, fish and vegetables, in a healthy way. Roasting is a suitable method for cooking large joints of meat and poultry; the meat should be basted occasionally to prevent it from drying out. Poultry retains its moisture if it is roasted in its skin, but the skin should be removed before eating, because this is where most of the unhealthy saturated fat is concentrated. Placing meat on a rack in the roasting tray is recommended because the fat is able to drain away. Some vitamins are lost in the meat juices caught in the roasting tray along with the fat; the fat can be skimmed off and the remaining juices can be used to make a sauce.
Fish should always be baked quickly in a relatively high heat to prevent it becoming tough. Wrap fish in foil or parchment and allow it to cook in its own juices.
Roast vegetables are healthier if they are cooked separately rather than in the meat fat. Potatoes respond particularly well to baking; baked and eaten in their skins, they are an excellent source of fibre.
Stir-frying and steam-frying
The technique of stir-frying chopped meat, fish and vegetables is a healthy way to fry as it demands little fat. The Chinese wok is designed to cook food quickly at a high temperature, so the food docs not absorb much oil. The food must be constantly turned to prevent browning. Meat and fish remain moist and vegetables stay crisp and retain most of their nutrients. An even healthier alternative is to steam-fry, adding no oil, but instead steaming the food in a watery sauce, such as soya sauce, water and lemon juice. For steam-frying, it is best to use a pan with a heavy base and a sealing lid.
Shallow and deep-fat frying can be used to cook meat, poultry, fish and vegetables. The main health risks associated with these methods concerns the amount of oil used, the temperature it reaches, and the length of time for which it is kept hot. When oils reach smoking point, or are kept at very high temperatures for 15 minutes or more, chemical changes lead to the formation of free radicals – highly reactive chemicals that can damage cells in the body. These chemicals have been linked with degenerative diseases such as heart disease and cancer. It is now known that poly-unsaturated oils turn into harmful trans fats when heated. Some nutritionists therefore recommend olive oil, butter and butterfat (a combination of milk and cream that contains less water than ordinary butter and can therefore produce a better result) as safer choices for frying food. Fresh oil should be used each time; oils must not be heated to smoking point and food should not be fried at very high temperatures for more than a few minutes.
During shallow frying, foods are fried at a high temperature in a small amount of oil or fat. This method can be used for meat, poultry, fish, vegetables and eggs. Shallow frying is preferable to deep-fat frying because it requires much less oil or fat. Therefore, there is less fat for the food to absorb. Vitamins are lost at the high temperatures this method requires, however, and the health concerns regarding trans fats and free radicals still apply.
Often considered to be the least healthy method of cooking, most nutritionists advise against deep-fat fried foods because of their high-fat, high-calorie content and the detrimental effects they have on health. Deep-fat frying requires fats to be heated to temperatures in excess of 200°C (392°F). This causes fats to be oxidized and essential fatty acids to turn into trans fats. Animals fed such oils have developed atherosclerosis (thickening of the artery walls). However, if the oil is not-heated to an appropriately high temperature, the food being cooked absorbs a great deal of fat. For these reasons, it is generally recommended that the consumption of deep-fried foods be kept to a minimum. If this method is used, choosing a vegetable oil instead of animal fat decreases the saturated fat content of deep-fried foods. Blotting the fried items on several layers of kitchen paper before serving lowers the fat content.
Vegetables are particularly suited to cooking by steaming – cooking times are short, and the vegetables are not immersed in water so vitamins are retained rather than lost in the cooking water. The vegetables are cooked until tender in a steamer (which is similar to a metal colander) placed above the boiling water. Steaming is particularly suitable for broccoli, asparagus, carrots, spinach, green beans and corn. It is also a better choice than boiling for longer-cooking vegetables such as potatoes, turnips and parsnips. Steaming is also an excellent method for cooking fish, as the hot vapour cooks the flesh quickly, while retaining its nutrients and flavour.
During boiling, water-soluble vitamins (vitamin C and the B vitamins) leach into the cooking water. When cooking vegetables, it is therefore a good idea to retain the cooking water and use it for soups, stews, sauces and stock. To minimize nutrient loss when boiling vegetables, bring the water to the boil before adding the vegetables to the pan. Alternatively, scrub the skins thoroughly and boil the vegetables in their skins, peeling them, if desired, after they have cooked.
Boiling destroys the toxic substances that occur naturally is some plants, such as butter beans (also known as lima beans) and runner beans.
When poaching, foods are briefly simmered in a shallow pool of liquid such as water, broth, or the juice from fruit or vegetables. It is a quick and healthy cooking method that uses no fat. Poaching can be done on a burner on the top of the cooker or in the oven, and is particularly suitable for fillets of delicate fish, such as sole, and for fragile fruits, such as pears.
Microwave cooking is an effective method for most vegetables and fish. It can also be used to defrost and reheat dishes. Vegetables and fish retain their moisture, colour and most of their nutrients. Vitamins and minerals in particular are conserved in vegetables because cooking times are short (approximately 24-50 per cent less than conventional electric or gas ovens), and little or no water is needed. Also, microwaving requires no additional fat. In order to prevent overheating and to avoid the dangers of exploding foods, the skin of vegetables such as potatoes and tomatoes must be pierced to allow steam to escape.