why nutrition is important

424

Introduction -

Food has many functions, not the least of them social. There is no good reason why healthy eating should not be enjoyable.

While books about diet and food fads abound in Britain, the United States and Australia, it is still difficult for the individual to find the basic facts about food that will enable a person to plan and follow a healthful diet geared to particular needs.

The purpose of this book is to provide such information. It answers many questions that arise every day, such as 'are there any vitamins in the frozen peas I'm eating?'. It is also designed to help readers understand the principles of good nutrition for themselves and their families. They can then plan, in an informed and intelligent way, their food intake under different circumstances.

 

WHY NUTRITION IS IMPORTANT

There is considerable truth in the adage 'You are what you eat'. The state of your body and how well it works depends to a large extent on how appropriately it is nourished. Malnutrition can be found in contemporary Western society and is not peculiar to developing countries.

Malnutrition occurs when a person's body is not adequately serviced by its food intake. Each individual's needs change under different circumstances. Moreover, the foods needed by an athlete, a grandmother, a growing boy, an office worker or a pregnant woman are not the same. Nutritional needs vary even from one office-worker to another, according to genetic make-up, level of activity, general state of health and environment.

Some groups of people who are at risk from nutrient deficiencies can be generally identified. These include those who are socio-economically disadvantaged; women during the reproductive years because of the added nutritional demands of menstruation and of pregnancy; the elderly; those who have a particular health problem, such as diabetes, faulty absorption of food or who are on certain medications; those with lifestyle problems such as cigarette smoking and alcohol abuse.

Diet and health

The most significant nutritionally related problems in industrialized nations are those health conditions that are the result of, or are made worse by, a diet that is not prudent:

  • overweight (obesity)
  • hardening of the arteries ( atherosclerosis), leading to reduced blood flow to the heart (coronary heart disease), brain (strokes), legs (pain on walking) and other organs
  • certain tumours, especially of the large bowel.

Diet can increase the risk of heart disease in several ways. Eating foods that are high in saturated fat, low in polyunsaturated fat and high in cholesterol can raise the level of cholesterol in the blood. When the blood cholesterol level is increased the risk of coronary heart disease is increased. Another kind of blood fat (lipid) known as triglyceride can also be elevated and increase the risk of heart disease. Conversely, when relatively more fruits, vegetables and wholegrain cereals are eaten the blood fats are lower.

High blood pressure (hypertension) also increases the risk of heart disease, strokes and kidney failure. Blood pressure is higher when sodium intake is high, potassium intake (an element obtained mainly from plant foods) is low, alcohol intake is high and there is excess body weight. Eating too much, with consequent obesity, increases the risk of heart disease by increasing the work of the heart, increasing blood pressure, and increasing blood fats; obesity also increases the risk of diabetes. Nutritional factors can also alter the 'stickiness' of some blood cells, called platelets; this contributes to hardening of the arteries and may result in a blockage of the artery. Some polyunsaturated fish oils reduce the stickiness of platelets and may account for the rarity of heart disease amongst fish-eating communities, such as the Eskimos.

As far as tumours or cancers are concerned, a number of interesting food factors are emerging from research. A food intake low in fat and cholesterol, high in dietary fibre from wholegrain cereals, with plenty of vegetables and little alcohol seems protective against large bowel (colon and rectum) cancer. The reasons for this are not yet known. The same kind of dietary pattern may also reduce the risk of tumours of lung, breast, uterus, prostate and pancreas. There is little evidence so far to suggest that food additives are significant in the development of cancer.

Diabetes is a condition where the blood sugar (glucose) is too high because not enough insulin is produced by the pancreas for the body's needs. The glucose spills from the blood into the urine, leading to a large loss of water as urine; thirst then follows. Broadly there are two types of diabetes, one where it is necessary to administer insulin from the time of diagnosis and the other where it is not. Amongst Caucasians in industrialized nations two to three people in every 100 are affected. When non-Caucasians adopt the food habits of affluent society, they appear to be particularly susceptible to diabetes; from 15 to 40 per cent of Australians of Aboriginal or Pacific-Islander descent suffer from diabetes. Being overweight is a particularly important risk factor for developing the type of diabetes where administered insulin is not usually needed. A diet with a high intake of high-carbohydrate, high-dietary-fibre foods and a low intake of fat seems protective against the development of this type of diabetes.

Since most premature deaths in affluent societies result from atherosclerotic disease of blood vessels (vascular disease), and from lung, breast and large bowel cancer, there is great potential for dietary change to increase life expectancy and, indeed, to reduce morbidity and chronic illness.

 

            Because health is so closely related to diet, nutritionists and public health workers have sought to identify the optimal diet. The first principle of an optimal diet is to ensure that the amount of food is right -- not too little and not too much. If a person's growth has proceeded satisfactorily and weight is appropriate, this particular goal is realized.

The second nutritional principle is to have as wide a variety of foods as possible. The greater the variety of foods you eat, the more likely you are to obtain the full range of nutrients required. Traditionally, and for most of human experience, as hunter-gatherers, people collected fruits, nuts, seeds, leaves, roots, caught small animals and fish, and hunted, with less success, larger game. This is the diet with which humans evolved; our bodies are designed to be serviced by the nutrients in such a diet. Another reason for emphasizing the importance of variety from a range of biological sources of food is that, if there is any toxic or harmful factor in a particular food, it will tend to be diluted to a level where it is not hazardous. The advent of food staples -- such as potatoes, wheat and rice - is more a reflection of agricultural practice and a way of feeding a larger number of people at a lower cost than of nutritional principle. Insofar as a staple is often unavoidable, it is best to have it unrefined so that as many nutrients as possible are consumed.

The third nutritional principle, related to the first, is to balance food intake with the rate our bodies use it up. In our society the balance is often not achieved, because our level of physical activity is so much less than that of our hunter-gatherer forbears. Important concepts nutritionists use in finding what the balance should be are 'energy density' and 'nutrient density'. The average person, with an average level of physical activity, needs a certain minimum of energy every day -- not less than 1200 kilocalories" (about 5000 kilojoules) per day. The more energy (kilojoules or kilocalories) there is per unit (weight or volume) of a food, the more 'energy dense' it is. The more nutrients there are for a particular amount of energy, the more 'nutrient dense' it is. Fatty foods are generally the most energy dense. Some are also nutrient poor, like butter and lard. Vegetables tend to be low in energy density and high in nutrient density. The less physically active we are, the less can we have energy-dense foods and the more we should have nutrient-dense foods.

Dietary guidelines

The pattern of disease in affluent society - obesity, vascular disease, cancers, diabetes, etc. -- is associated with a high intake of fatty meat and dairy products, a high intake of alcohol, a low intake of wholegrain cereals, fruits and vegetables, and a high intake of sodium (especially as salt). It is for these reasons that several countries have now developed dietary guidelines similar to the following:

    • eat a variety of foods each day
    • encourage breast feeding
    • prevent and control obesity
    • decrease total fat intake
    • decrease consumption of sugar
    • limit alcohol consumption
    • increase consumption of cereals, fruits and vegetables
    • reduce sodium intake
    • encourage water intake.

 

Encouragement of breast feeding is included in recognition of breast milk's unique properties, such as those protecting against infection, which cannot as yet be reproduced in infant milk formulas.

Average life expectancy in the twentieth century has increased. Yet among developed countries there is a hierarchy of life expectancy with, for example, Sweden, Greece and Japan being ahead of the United Kingdom, Australia, New Zealand and the United States. To some extent, these differences appear to relate to food intake pattern. It seems that much may be gained from analysing why this is so, identifying an optimal diet and following guidelines that promote it.

Food is not the only factor that can influence health; most health problems in modern society are 'multifactorial' in origin. But nutrition is clearly a very important factor. If you can establish healthy dietary habits in conjunction with attention to other factors (such as physical activity, smoking, stress, work environment), you will give yourself the best chance against ill health and for a long and active life.

Footnote:

*The amount of energy released from the food we eat is measured in units called kilocalories or sometimes Calories spelt with a capital C. Another unit of energy commonly used is the kilojoule. It is easy to convert kilojoules to kilocalories and vice versa:

1 kilocalorie = 1 Calorie
1 kilocalorie = 4.2 kilojoules (approximately 4)
1 kilojoule = 0.24 kilocalories (approximately 1/4)
1 megajoule = 1000 kilojoules

 

 

            - What is food ? -

Food makes your body work, grow and repair itself. The kind of food you eat can affect the efficiency of these processes. Body function and the food that sustains it is infinitely complex. Food is in fact one of the most complicated sets of chemicals imaginable.

Getting to know which nutrients are in which foods can help you to understand something of this complex relationship between your food and your body.

Chemicals in food

Food is composed of many different chemical substances - 'macronutrients' (major nutritional components that are present in relatively large amounts, such as protein), 'micronutrients' (major nutritional components that are present in relatively small amounts, such as vitamins), water, and roughage (dietary fibre). Many other components can also be present in food.

Food may contain colours (natural and synthetic), flavours, pharmacologically active substances (such as caffeine, steroids, and salicylates, which chemically affect the body), natural toxicants (naturally occurring poisons, such as cyanide), additives, and various contaminants (substances resulting from a contaminated environment, such as pesticides). Even characteristic flavours such as those of oranges and passionfruit can depend on the presence of a dozen or more chemicals.

The chemical nature of food is changed by storage, preservation and, especially, by cooking. Food chemicals can also interact amongst themselves within the body. For example, the availability to the body of iron from plant sources depends on the amount of vitamin C present in the food eaten. The way in which carbohydrate is absorbed from the bowel depends to some extent on the presence of dietary fibre, even though the fibre itself is not absorbed.

Physical form of food

Food is also more than just the chemicals it contains. Its physical characteristics are important. The size of food particles can affect the extent to which nutrients are digested and made ready for absorption by the body. For example, eating an intact apple has nutritional value different from drinking all the same chemicals in an apple purée. Ground rice is more rapidly digested than unground rice. Nutrients can be more easily absorbed from peanut butter (paste) than from peanuts eaten whole.

Acid or alkaline

The acidity and alkalinity of food are physical properties often thought to be important. In fact, they are only important insofar as they might alter the rate of emptying of the stomach, digestion in the small bowel and the acidity or alkalinity of the urine. Our bodies can cope with a wide range in food acidity and alkalinity without much problem. Acid foods are generally sour while alkaline foods often have a slightly soapy taste. The use of sodium bicarbonate (baking soda) can make foods alkaline. It can also cause loss of vitamin C and contribute to our intake of sodium.

 

            - What happens to the food we eat? -
(Food and Body Function)

The nutrients in food are used by our bodies in varying ways. Each nutrient plays some part in normal body function (that is, body physiology).

Not all components of food are nutrients, and not all nutrients are essential to life. Some nutrients may have important physiological functions without being absorbed from the gut, for example dietary fibre. Dietary fibre, while not being essential to life, is associated with health because of its role in the correct functioning of the bowel. Its absence may increase the risk of bowel disease.

Although recommendations about nutrient intakes are made in terms of daily intakes, not all nutrients are needed every day. Most can be stored to a lesser or greater extent in our bodies. The macronutrients that provide energy are stored in the liver and muscles in the form of a carbohydrate called glycogen, and in fatty tissues (adipose tissue) and muscles in the form of fats, known as triglycerides. The situation for micronutrients varies. Fat-soluble vitamins, such as vitamin A, tend to be stored in liver and fat and do not need to be replenished every day; they can last for weeks if the stores are good. In general, water-soluble components like vitamin C are quickly excreted in the urine. But some water-soluble nutrients such as vitamin B-12 and folacin (folic acid) can be stored for years and months, respectively, in the liver. Some nutrients, for example calcium and phosphorus, are in effect stored in bone.

Although not every nutrient is needed every day, it is safest to 'top up' regularly through a consistent pattern of eating. Nevertheless, undue concern about particular food preferences, for example about children who seem to want one kind of food and not another for a few days. is probably unnecessary. As long as a variety of foods are eaten in the longer term, the range of essential nutrients should be provided.

- Energy balance -

If you eat more than your body needs to keep it working efficiently, you will get fat. Many slimming diets prefer not to emphasize this displeasing but basic fact.

When energy intake equals energy needs, our bodies are in 'energy balance'. This means that if you are fully grown, or are growing normally, and your weight is within certain limits (those that conform to longest life expectancy and least illness), you have achieved energy balance. You achieve it by balancing, on the one hand, your total energy intake, and, on the other, your level of activity. The more active you are, the more energy you need.

Energy intake, which used to be measured in calories or kilocalories, is now measured in kilojoules (kJ). To convert calories or kilocalories to kilojoules multiply by 4.2 (approximately 4). Although the number of kilojoules in a particular food is numerically larger than the number of calories or kilocalories, the amount of energy is the same. It is rather like measuring time in minutes or seconds. One hour is still the same amount of time whether it is expressed as 60 minutes or 3600 seconds.

People differ in the efficiency of their energy expenditure. This may be due to differences in efficiency of movement, or because some people are not as efficient as others in burning up their 'fuel' supplies (that is, their 'metabolic efficiency' is lower). Thus, one person may eat much more than another, with equivalent levels of activity, and yet remain similar in weight. The more 'energy-efficient' person needs to be more careful about eating too much to avoid becoming overweight. However, the same person would survive better if food supplies were short.

Energy needs vary with your age and weight, as well as with your level of activity. 

Energy is also used, with varying efficiency, to maintain body temperature, to store fuels after a meal and to form bodily wastes, So even when you are not being active your body needs energy for vital processes. This minimum level of energy expenditure is known as the 'basal metabolic rate'. It is what keeps you alive even if you are completely at rest, fasting and at a comfortable temperature.

CONTROLLING BODY WEIGHT

When our bodies are not in energy balance, excess energy is stored as fat (in adipose tissues). Women normally have more body fat than men, and this should be taken into account when considering whether to conform to the fashion to be very slim. 

If you are on a weight-reduction programme, remember that body water is the main constituent lost during the first few days. It is only after 2 to 3 weeks of dieting that the loss is mainly fat. At this stage, a daily energy intake that is about 500 kilocalories (2000 kilojoules) less than the intake actually needed at a particular level of physical activity will lead to a weight loss of approximately 1 kilogram per fortnight. Remember also that not all people expend energy with the same efficiency.

APPETITE CAN CONTROL HOW MUCH ENERGY (FOOD) WE CONSUME

Appetite has an important role in controlling energy intake. When we are physically active, appetite is more correctly related to energy need than when we are inactive. At low levels of physical activity, we are more likely to feel hungry and to eat more than we need.

Also, a diet that is low in fat and high in carbohydrate and dietary fibre seems to allow appetite to be more correctly attuned to energy need. Because fatty foods are so palatable, more of them tend to be eaten than our bodies really need. They are also more energy dense than high-carbohydrate, high-dietary fibre foods.

ENERGY DENSITY

A high-energy-dense food has more kilojoules (or kilocalories) than the same amount of a low-energy-dense food.

The more energy dense a food is, the less of it we can eat to provide a given amount of energy. Conversely, the less energy dense a food, the more we can eat to provide us with the same amount of energy.

The more water and dietary fibre, and the less fat and alcohol in a food or drink, the less energy dense it is.

NUTRIENT DENSITY

The greater the number of essential nutrients, and the larger the amount of them a food contains, the more 'nutrient dense' it is. Often foods with low energy density are quite nutrient dense, as, for example, wholegrain cereals and leguminous vegetables (like peas and beans). Some foods can be both nutrient dense and energy dense, such as a piece of steak.

 

Nutritional Status -

ASSESSING YOUR OWN NUTRITIONAL STATUS

You should be able to get an indication of whether you are consuming too much or not enough of any particular nutrient. However, this exercise is designed to help you learn about a healthy diet rather than be an exact guide. If you want to know precisely, or suspect a health problem is due to nutrient deficiency or excess, you should consult a doctor.

 

- Food Additives and Colours -

Food additives

Food additives are substances that are intentionally added to modify visual appearance, taste, texture, processing, or the storage life of food. In most countries the use of food additives is controlled by law. Only certain permitted additives may be used and then they are only allowed in particular foods in amounts not exceeding a stated maximum concentration.

Before an additive is approved for use in a particular food it must be established that it is safe, and also that a comparable product cannot be produced without using the additive. Sometimes it is difficult to decide from laboratory tests with animals whether a substance will be harmful to people when consumed in small amounts over a long time. It is wisest to err on the side of safety. If appropriate animal tests indicate a potential hazard for people, then approval for use of the additive should not be given. From time to time there is concern when additives that were once considered to be safe are subsequently shown to be potentially hazardous. This is because decisions approving additives were made on the best evidence available at the time. As further information becomes available or new test procedures are developed, the original decision may have to be modified. This may involve limiting usage or even withdrawing approval for a particular additive.

Many of the foods we now take for granted could not he produced without the use of food additives. We use cake mixes, requiring only addition of liquid and baking; soups and mashed potato, requiring only water and heating; the use of additives in bread maintains freshness and retards spoilage from mould and bacteria. Free-flowing salt, sausages and prepared meats, salad dressings, processed cheese , and peanut butter could not be conveniently presented without food additives.

When a food additive is used, the label must list all the additives added to the food. The additive can be designated on the label by its chemical name or by a general class name. Class names used for designating groups of food additives on food labels are shown in the following table. In most cases, the class names describe the function the additive performs in food. To identify specific additives within the class, a code number has been allocated to most approved additives. When a class name is used it must be followed by brackets containing the number corresponding to the specific approved additive. For example, sodium benzoate, which has been allocated the number 211, would appear in the list of ingredients as 'preservative (211)'.

With the exemption of flavours which are not designated by a code number, this system will allow those interested to identify foods containing specific additives, including colours. A list of food additives and their code numbers appears in Appendix A.

CLASSIFICATION OF FOOD ADDITIVES

Anti-caking agents
Antioxidants
Artificial sweetening substances
Bleaching agents
Colours
Emulsifiers
Enzymes
Flavours
Flour treatment agents

Food acids
Flavour enhancers
Humectants
Minerals
Mineral salts
Preservatives
Propellants
Thickeners
Vegetable gums
Vitamins

 

Although some foods are exempt from the normal ingredient labelling requirements (alcoholic drinks, most types of cheese other than processed cheese and cheese spread, the flavour components in flavour essences, and certain foods in small packages), when antioxidants, colouring, flavouring and preservatives are used, the label must indicate their presence. Under certain circumstances it is possible that an additive present in a food which is used as an ingredient in the preparation of another food will 'carry over' without being declared in the ingredient list on the label. For example, if margarine is used in the preparation of a cake, margarine will appear in the ingredient list rather than the individual components of margarine. The presence of such 'hidden' additives may need to be considered when planning some dietary regimens.

 

- Toxicity in Food -

Is natural always good?

The notion that 'natural' food may be harmful is not widely appreciated. The terms 'health', ‘organic', 'natural', 'unprocessed', 'no added chemicals' when applied to food suggest that the food is safe or more nutritious than its conventional counterpart but this is not necessarily true. All food is made up entirely of chemicals. In addition to well-known nutrients such as carbohydrate, fat, protein and water, food contains many other substances, often in very small amounts.

Any substance in food may have a degree of toxicity or 'poisonousness', whether it is natural, deliberately added, or a contaminant. There is nothing special about natural chemicals in food and no distinction should be made between natural and other substances when deciding if a food is likely to be hazardous. For example, a potato contains a number of poisonous substances such as nitrate, arsenic and solanine but in the amounts in which potatoes are normally eaten these natural substances are not hazardous. For this reason it is important not to consume large amounts of a small number of foods, as in some faddist diets, but to consume a wide variety of foods. This not only minimizes the amount of a particular potentially hazardous substance but also ensures that a range of essential nutrients are consumed.

A number of substances that occur naturally in food and have either caused illness or are suspected of being hazardous to health. Usually these effects have occurred only when excessive amounts of a food containing these substances have been eaten. In fact, for most of us there is little hazard from these foods. The concentration of these poisonous substances is so low in the food we eat that we would have to consume huge amounts over a long time for the toxic effect to show up. Nevertheless, it is import ant to realize that there are many potentially hazardous substances in our diet without any obvious effects on our health, and that this applies equally to 'natural' and processed foods. Natural foods can be harmful if they are contaminated with excessive amounts of environmental contaminants, or aflatoxin or other mycotoxins produced by some moulds.

Herbal teas

Herbal teas have become popular with an increasing number of people. Herbal and 'bush' teas contain a large number of different components, many of which have not yet been assessed for safety. Some teas can lead to disturbing effects. Tea made from the South Pacific kava plant has been associated with impaired breathing, vision and hearing, and other symptoms. Comfrey and tea made from the roots of sassafras contain substances that have caused cancer in laboratory animals. In addition, some teas can interfere with the therapeutic value of some drugs that are taken at the same time. The heavy consumption of these teas is not to be recommended. Tea, coffee and cola-type drinks contain caffeine (about 30, 40, and 10 milligrams per 100 millilitres respectively). Although individuals react differently to caffeine, the heavy consumption of these drinks can cause, in addition to stimulation, nervousness, increased urination, upset stomach and irritability (Chart 49).

 

            - Processing Food -

Processing can affect the nutrient content of food

There are many different forms of processing to which food may be subjected before we eat it. All of these processes have some effect on the nutrient con tent. Although foods are often compared before and after processing, a better comparison is at the stage when the food is eaten. For example, during the freezing of peas there is about a 10 per cent loss of vitamin C. But because they require a shorter cooking time than fresh peas, there is virtually no difference between the vitamin C content of fresh and frozen peas as they appear on our plate.

The nutritional changes that occur in the commercial preparation of food do not differ much from those in the same food prepared in the home. Both types of food preparation involve some form of processing. There may be differences in palatability and the food manufacturer may use cheaper ingredients such as emulsifiers, cereal fillers and synthetic flavours. This may be partially off-set by the fresher foods usually available to the manufacturer. The effect of the different types of processing on nutrients is discussed below.

 

            The stability of nutrients in food depends on their environment.

Nutrients can be lost to varying degrees depending on whether the food is exposed to light or air, acid or alkali, the temperature and their ability to dissolve in water. Generally the losses of carbohydrate, fat, protein, vitamin K, niacin, biotin and elements are small during processing and storage. Greatest losses are usually seen with vitamins B-l and C, with intermediate losses shown by vitamin A, provitamin A and vitamins D, E, B-2, B-6, B-12, pantothenic acid and folacin.

Losses may be due to destruction of the nutrient or by dissolving in water that is later thrown away. The presence of acid (from other foods or addition of vinegar) or alkali (from other foods or added sodium bicarbonate (baking soda)) can cause destruction of some vitamins.

The stability characteristics of nutrients are shown in 

 

NUTRIENT

STABILITY CHARACTERISTICS

Vitamin A and provitamin A

Reasonably stable during processing
Losses occur when dehydrated foods are exposed to light and air

Vitamin D

Relatively stable but sensitive to exposure to air and light

Vitamin E

Relatively stable but foods cooked in oil can have large losses

Vitamin K

Relatively stable but sensitive to light

Vitamin B-1 (thiamin)

Large losses under neutral and alkaline conditions where baking powder is used (e.g. cakes). Dissolves in cooking water. There is reasonable retention in cooked meat

Vitamin 8-2 (riboflavin)

Very sensitive to light. Relatively stable to most home cooking methods. Losses can occur in drippings from meat

Niacin

Stable to most processing. Dissolves in cooking water

Vitamin B-6

Moderate retention during most processing. In milk it is sensitive to light

Vitamin B-12

Moderate retention, but losses occur when heated under mild acid and alkaline conditions

Folacin

Relatively stable but large losses can occur on cooking. Presence of copper aids destruction

Pantothenic acid

Relatively stable during home cooking but losses occur in meat drippings and cooking water

Biotin

Good retention during most home processing

Vitamin C

Relatively unstable and losses occur from exposure to air, light, heat and copper. Dissolves in cooking water

Elements

Stable to most processing but losses can occur by dissolving in cooking water

 
     
 

 

 

- Storage Life of Foods -

These storage lives are only a rough approximation as the actual life of a particular food will depend on the initial quality, the type of processing, the storage temperature, the type of packaging, the moisture content of the food, the extent of contact with air and other factors.

There is no precise moment at which a food suddenly becomes undesirable. There is just a gradual deterioration; the colour may darken, the texture may soften or there may be loss of flavour or development of an off-flavour. There comes a time when there is a discernible change from the initial quality. The detection of this change will vary between individuals.

Changes that occur in a food when stored at temperatures higher than recommended are cumulative and cannot be reversed by returning the food to lower temperatures. The longer the storage time, the greater the deterioration in nutritional quality and palatability. In extreme cases the action of microbes can make the food unsafe to eat. Modern methods of food preservation, such as freezing, refrigeration and canning, considerably extend, above the normal, the time taken for a comparable loss of nutrients and eating quality.

Many food labels now include a date mark that gives an indication of the expected life of the food before a noticeable deterioration in quality occurs. The significance of the different forms of date marking is discussed on page 24. The 'use-by' or' minimum durable life' date is only applicable if the food is stored under the conditions specified on the label. If no special storage conditions are required normal cupboard storage should give the stated storage life.

- Storage Life of Foods -

Frozen foods

If temperatures are carefully controlled at -18°C and the food was initially of high quality then longer storage times can be achieved. However, most home freezers are used for freezing as well as storage. This results in temperatures rising above -18°C, which decreases optimum storage life. Some deterioration in quality may have already taken place before the food is frozen; for instance it may have been left in a hot car while shopping. At -180°C loss in quality is very much slowed but not completely stopped.

These slow changes, which limit the storage life, do not have a marked effect on nutrient content but eventually cause a noticeable change in eating quality. Frozen foods do not become unsafe to eat even if kept for many years at -180°C (see here for safe handling of frozen foods).

To remain aware of storage time, each package should be marked with the date as it is placed in the freezer.

Canned foods

Some canned hams and imported fish must be refrigerated during storage. Always read labels to see if any special storage conditions are needed. Longer storage times result in a gradual decrease in quality and nutrients, but the foods are still quite safe to eat.

Do not open any cans that are swollen or leaking as this indicates faulty processing; and do not buy cans that are dented or rusted.

Once opened, if the contents are not eaten, they should be covered and stored in a refrigerator. Some acid and salty foods such as fruit juices, tomatoes and rhubarb should be removed from the can before refrigerating.

Home storage of food

Fruit and vegetables

The storage lives of fruit and vegetables vary enormously, being influenced by the maturity and quality of the produce at purchase and also the particular variety. Generally, the lower the storage temperature (but not below O°C), the longer the produce can be stored. However, some fruits and vegetables, particularly bananas and most other tropical fruits, are damaged when kept in a refrigerator. Many fruits and vegetables can dry out in a refrigerator and it is a good idea, once they are chi lied, to place them in the crisper or in a plastic bag with a few holes in it. If a refrigerator is not available, find a cool dry place for storage.

The storage times apply to sound, mature, ripe produce. Changes in nutritional quality and palatability are gradual and there is often no sharp cut-off point at which the food is no longer acceptable. Consequently. storage lives vary consider ably, and those listed in the tables are for guidance only.

Fruits and vegetables not fully ripe when purchased will have a longer storage life. Fruits ripen best at about 20°C and the unripe fruit can be removed from the refrigerator and ripened as needed. For example, unripe avocados will keep in a refrigerator for up to 3 weeks, whereas the ripe fruit will keep for a few days only. Pears bought hard and green can be kept in a refrigerator for fairly long periods. those that are bought ripe will only last a few days. Potatoes keep quite well in a cool dark place. You should discard any potatoes with large areas of green skin as they contain a poisonous substance called solanine. Potatoes with a small area of green are safe if they are deeply peeled and the peel discarded.

Other foods

The expected storage lives of foods other than fruit and vegetables are only approximate and depend very much on how the food was treated after purchase. If, for example, butter was left in a hot car for a short time, then the storage life until a deterioration in quality was noticed would be dramatically reduced. Similarly, if the packaging of breakfast cereals, for example, was damaged or opened, the storage life could not be expected to be the same as for an unopened package.

 

- Health Problems Associated -
- with Some Foods -

How to avoid food poisoning

Micro-organisms are present almost everywhere: in the air, soil, on our hands, in our bodies and in food. Not all of these tiny organisms are harmful and some are essential for good health and the production of food and drugs. Some can cause food spoilage and illness. Most forms of food processing either destroy these micro-organisms or reduce their numbers to safe levels.

Most micro-organisms can grow and multiply at temperatures between 15°C and 63°C, with most rapid growth occurring around 37°C. It is important that food is not held in this temperature range for long periods, as the food may become contaminated with large numbers of micro-organisms and cause illness. At higher temperatures most harmful microorganisms are destroyed, and at lower temperatures, such as in the refrigerator (1-4°C) or the deep freeze (-18°C), there is little or no growth. When cold foods are warmed, the micro-organisms will start to grow and multiply. Therefore it is important to heat food rapidly. The shorter the time spent in the temperature range where rapid growth of micro-organisms occurs, the lower the chance of food poisoning.

Some frozen foods such as vegetables, precooked foods and smaller cuts of meat can be cooked directly from the frozen state. Large cuts of meat should be thawed prior to cooking or extra cooking time should be allowed to ensure that the interior temperature reaches 71°C. Thawing is best carried out by placing the food in a refrigerator, allow at least 16 hours per kilogram. If not used after thawing it can be kept in the refrigerator chilling section for 1 to 2 days. Food that has been allowed to thaw in the kitchen should be cooked soon after thawing and not stored in a refrigerator. Packaged frozen foods have instructions on how best to prepare the food for eating. It is not advisable to re-freeze foods that have been thawed.

Because micro-organisms are very widespread, contamination of food can occur easily. Personal hygiene and a few precautions can prevent this leading to food poisoning and illness.

 

- Health Problems Associated -
- with Some Foods -

Food sensitivities

It is important that possible causes of the disorder other than allergy be considered. A wheezing patient could have asthma due to an allergy, but the wheezing could also be due to bronchitis, infection, heart disease or cancer. Diagnosis of food allergy needs careful medical interpretation of the patient's history. This should include dietary background and the effects of 'elimination' diets, in which the suspected food(s) have first been excluded, and then reintroduced to the patient to compare the results. Although there may be improvement after the elimination diet, with a return of symptoms when the food is reintroduced, there can still be some doubt whether food allergy is the cause of the condition.

There are many causes of intolerances or sensitivities to food, and not all of them are due to allergy. For example, coeliac disease can produce effects similar to cow's milk allergy.

The foods most commonly responsible for allergic reactions are listed in Food additives have occasionally been thought to cause allergic reactions. The additives most commonly implicated are tartrazine, a yellow dye used in many foods, beverages and pharmaceuticals; also, benzoic acid and sulphur dioxide, which are used as preservatives in some fruit drinks, cordials, soft drinks and wines.

Migraine and food

A variety of factors have been reported to trigger migraine attacks. Stress is probably the most widely recognized trigger for migraine. Stress may be brought about by emotional shock noise, glare or some other condition. Some studies on migraine have claimed that diet is a trigger factor. Between 5 and 30 per cent of migraine sufferers believe that food plays a part in their migraine. Much of the evidence linking diet and migraine is scientifically unsound. It frequently relies on the patient recognizing a link between the eating of a certain food and the attack Such links may be difficult to establish, particularly if the food responsible is consumed up to 24 hours before the attack .

Many other foods are implicated, but less frequently. There have been conflicting results from scientific studies examining the effects of food on migraine sufferers; probably a combination of factors is involved in triggering an attack It may be that there is a spectrum of response to dietary items, varying from very mild to very intense. With some sufferers, a particular food might always precipitate an attack, while with others, the food trigger may only be effective in combination with other factors, such as hormonal change or stress. Diets that avoid certain foods can have serious nutritional consequences if maintained for long periods, depending on the number and type of foods avoided, and they should only be followed under the supervision of a doctor or dietitian.

 

The Feingold diet and hyperkinesis

The name hyperkinesis refers to a broad range of symptoms seen in some children. These include physical overactivity that is inappropriate for the task, short attention span and other abnormal responses.

Some years ago Dr Ben Feingold, of the Allergy Department of the Kaiser-Permanente Medical Centre in San Francisco, advanced the hypothesis that salicylates (chemicals that occur naturally in some foods), food flavours and food colours were associated with hyperkinesis and learning disabilities in some children. Feingold claimed that approximately 50 per cent of children with hyperkinesis and learning difficulties improved when kept on a strict diet that excluded foods containing salicylates and artificial colours and flavours.

Many studies have been conducted to investigate this hypothesis. The results of the studies are uncertain but it is quite clear that the improvement rate is far lower than that originally claimed.

 

IMPORTANT TEMPERATURES IN
FOOD PREPARATION

Physical
Events:

Microbial
Events

 

 

 

   

 

 

water boils

 

 

 

 

 

most
microbes
are
destroyed
in this
region

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

slow growth

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

rapid
growth

 

hot day

 

 

 

 

 

normal room
temperature

 

slow
growth

 
 

 

 

 

 

refrigerator

 

 

 

 

 

water freezes

 

food poisoning
microbes are
dormant but
multiply on
reaching
warmer
temperatures

 

 

 

 

 

Freezer

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

HOW TO AVOID FOOD POISONING

PERSONAL HYGIENE

  1. Wash your hands before preparing food.
  2. Do not smoke or comb hair when preparing food.
  3. Cover any cut or pimple with dressings.
  4. Do not handle pets when preparing food.
  5. When tasting food do not return licked utensils to the food.

PRECAUTIONS WHEN PREPARING FOODS

  1. Keep all cooking utensils and surfaces clean. Discard cracked and chipped utensils and crockery.
  2. Do not use the same knives, chopping boards etc, for both raw and cooked food without first washing them.
  3. Keep food as cold as possible.
  4. Do not store raw food where it can contaminate cooked food. Water or blood from raw meat or fish can cause contamination by dripping onto cooked food stored below.
  5. Heat food as rapidly and cook as thoroughly as possible. Remember the inside temperature can be much lower than that on the surface.
  6. If the food is not to be eaten immediately after cooking, cool it as quickly as possible and keep it in the refrigerator until it is ready to be served or reheated. Large pieces of food should be sliced into smaller pieces to allow it to cool more rapidly.
  7. Do not keep food warm; keep it either hot or cold.
  8. When reheating food, heat quickly and thoroughly, so that even the middle of the food pieces have reached a high temperature.
  9. Handle cooked food as little as possible; use serving tongs etc.
  10. Discard any food that has gone 'off' (off-odour, mouldy, slimy). Storing at lower temperatures will not stop further deterioration.

 

 

SYMPTOMS SOMETIMES DUE TO FOOD ALLERGY

Digestive system:

- Diarrhoea
- Vomiting
- Abdominal pain

Skin:

- Hives
- Rashes
- Eczema
- Swelling or puffiness

Respiratory system:

- Allergic rhinitis
  (hayfever, sinus trouble)
- Asthma
- Wheezy bronchitis

Behavioural and nervous system:

- Headache
- Irritability
- Fatigue
- Convulsive seizures
- Depression

Others:

- Dizziness
- Ringing in the ears (tinnitus)
- Aches and pains in muscles and joints
- Bladder inflammation

 

 

 

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