Last partial update: June 2019 - Please read disclaimer before proceeding.
Dietary nutrient groups
The nutrients in food are divided into two main groups; those present in large amounts, called macronutrients, and those in small amounts, called micronutrients. The macronutrients consist of carbohydrates, fats, fibre and protein, while the micronutrients consist mainly of vitamins and minerals. The table below indicates the energy content and functions in the body of each of these groups. The roles nutrient groups play in causing and preventing illness in Western society are discussed in detail throughout this book. It needs to be emphasized that the majority of Australian diets are not nutrient deficient. In fact, most Australian diets contain too much energy and too much fat. There are, however, a few groups of people who are likely to have micronutrients deficiencies. This issue is discussed in the sections on micronutrients, vegetarian diets, and osteoporosis. The role of antioxidants in disease prevention is also discussed later in this section.
Function and energy content of nutrient groups
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Nutrient |
Foods sources |
Energy content |
Function / use |
|
cal |
kJ |
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Fat - Fatty acids |
Mainly animal sources and vegetable oils. |
9 |
37 |
Mostly stored as fat for later energy use by the body when needed. Also an integral part of cell membranes. |
Fat - Cholesterol |
Lambs brains, liver, eggs and some seafood. |
Synthesis of body compounds including cell membranes and body chemicals, such as steroid hormones. |
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Alcohol |
Alcoholic beverages |
7 |
29 |
Used for energy. Alcohol is not converted to fat but is metabolized to provide energy before fat and thus reduces the rate of fat breakdown. |
Protein |
Meats, fish, poultry, eggs, milk products, cereals, nuts and legumes, including soy beans, lentils, beans and peas |
4 |
17 |
Mostly used in the synthesis of body components. Only rarely used as an energy source, such as in starvation. |
Carbohydrate - Starches (complex carbohydrates) |
Pasta, potato, breads, cereals, fruit, legumes |
4 |
16 |
Provides energy for the body’s functions and some energy storage. It is usually stored as glycogen in the liver (and the muscle) but may be converted to fat if consumed in excess. (Glycogen is just many glucose molecules joined together.) The sugar that circulates in the blood and provides energy for the body is glucose. The brain relies almost solely on this glucose for energy and thus it is very important for blood glucose levels to be maintained. |
Carbohydrate - Simple sugars (sucrose, glucose, fructose, lactose) |
Fruit, honey and other sweet syrups |
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Fibre |
Bread, cereals, vegetables, fruit. |
0 |
0 |
Fibre keeps the bowel functioning normally and has a role in protection of the bowel from cancer causing substances. Soluble fibre can reduce blood cholesterol levels. |
Vitamins and minerals |
A wide variety of foods is needed, especially vegetables, fruit, low-fat dairy and lean meat. |
0 |
0 |
They are essential for the synthesis of many body components, especially enzymes. These nutrients have no significant energy function. Some are also important antioxidants. |
Water |
Fluids, fruit and vegetables |
0 |
0 |
70% of the body is composed of water. |
The major groups listed in the above table (and other nutrition topics) are dealt with in detail in other sections of this web site. (Links to these sections are listed below.)
Vitamins and minerals
Vitamins are a group of nutrient compounds that the body needs but cannot produce itself in adequate amounts. Thus, they must be obtained, at least in part, from the diet. All minerals need to come from the diet.
The only way to obtain the required amounts of all nutrients is with a well balanced diet. (Click here to access information regarding a healthy diet.) Eating is a central part of life and meal times should be one of the key foundations upon which households build their lives as healthy eating patterns provide both physical and social health.
The requirements for each vitamin and mineral vary according to age group and it is unnecessary (and beyond the scope of this web site) to detail all these amounts, mainly because, as a general rule, Australians do not need to take vitamin or mineral supplements as their diet provides adequate amounts. Those wishing to find out more about individual vitamins and minerals can do so by accessing the National Health and Medical Research Council’s recent (September 2005) and its very comprehensive publication on this topic; Nutrient reference Values for Australia and New Zealand including recommended dietary intakes. (It is available free on their web site at: www.nhmrc.gov.au/publications/synopses/n35syn.htm
There are, however, some situations in Australia where micronutrients are deficient. This can occur either because the nutrient is generally marginally deficient in the diets of most Australians or because a particular type of diet is deficient in a particular nutrient(s).
1. Specific deficiencies that effect the population generally.
These are discussed below or in other parts of this book.
- Folate: Folate supplements for women of child bearing age. These should be taken by any woman who has any likelihood of becoming pregnant as supplements have been shown to significantly reduce the risk of neural tube defects, a group of serious abnormalities that occur early in the life of the developing foetus. To be helpful, the woman needs to be on them when she becomes pregnant.
- Calcium: Calcium supplements in those with a low calcium intake, particularly in post-menopausal women.
- Iron: Iron intake in women (and men) with diagnosed (by blood tests) iron deficiency and no other underlying cause, such as blood loss from a cancer.
- Iodine
- Zinc
- Magnesium
2. Specific population groups who are likely to have deficient intake of minerals and vitamins and require a multi-vitamin / mineral supplement.
- Frail aged people (See section on malnutrition in the elderly)
- Some vegetarians (See vegetarian diets below.)
- People with multiple food allergies or intolerances. (See separate section on food allergies and food borne illness)
- People who chronically abuse alcohol who are likely to be deficient in vitamins (especially vitamin B1).
- People with diseases affecting their bowel that reduce their ability to absorb vitamins and minerals from their diet. Such diseases are relatively uncommon and beyond the scope of this resource.
- People with inadequate diet due to poverty or bizarre eating habits.
Information about specific minerals
Sodium
Most Australians have an excessive intake of sodium in their diet. This is an important health problem as it significantly increases the risk of developing or worsening high blood pressure; a problem occurring in about 30 per cent of Australian adults. Thus, everyone needs to know which foods contribute to their dietary sodium load and how to decrease this load. This topic is dealt with in detail in the section on hypertension (See separate section on dietary sodium and lowering blood pressure.)
Iron
Iron deficiency can be a problem for a considerable number of people, including vegetarians (due to an inadequate intake / absorption), menstruating women (due to increased iron loss via menstrual blood loss) and pregnant / lactating women (due to increased requirements). Reduced dietary intake, especially from haem-sources (see below), mean that women athletes and adolescent girls are especially at risk. Overall, about 20% of women of childbearing age have low iron stores.
Iron deficiency is te most common nutritional deficiency in infants and is more common in infants fed exclusively with cows milk formula and breast fed infants where the introduction of solids is delayed past six months.
Dietary iron requirements* |
|
Age / sex |
Daily requirement (in mg/day) |
Infants - 0 to 6 months breast fed |
0.5 |
Infants - 0 to 6 months bottle fed and pre-term infants |
3 |
Infants - 7 to 12 months |
9 |
Children - 1 to 3 years |
9 |
| Children - 4 to 8 years | 10 |
| Children - 9 to 11 years | 8 |
Adolescents - 12 to 18 years |
11 (males) to 15 (females) |
Adult males |
8 |
Adult females - Menstruating |
18 |
Adult females - Postmenopausal |
8 |
Adult females - Pregnant |
27 |
| Adult females - Lactating | 12 |
* Vegetarians may require levels up to 80% greater than those mentioned in this table as their dietary sources of iron are less well absorbed. |
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Iron is present in many foods but some forms are better absorbed than others. The more soluble, ferrous (Fe++) form (haem-iron) is much more easily absorbed from the bowel and this is present in ‘haem-containing’ foods such as meat, kidneys, liver, fish, pork and poultry. The absorption of iron from ‘haem-containing’ foods can be significantly increased by consuming them with green leafy vegetables. The insoluble, ferric (Fe +++) form of iron (non-haem iron) is much less readily absorbed (about 15 per cent) as it binds to other non-absorbed compounds in food. This type of iron is present in ‘non-haem-containing’ foods such as cereals, wholemeal breads, vegetables, brown rice, pasta, nuts and eggs (i.e. sources in vegetarian diets).
Consuming vitamin C (e.g. a glass of orange juice) can increase the iron absorbed from non-haem sources, as can consuming it with haem sources. On the other hand, absorbtion is deceased when the iron-containing food is consumed with tannins in tea and red wine, zinc, coffee, phylates in cereals, and calcium. (Calcium supplements are the main problem with regard to calcium intake reducing iron absorption. Milk intake is an insignificant issue.)
Overall, only about 25 per cent of iron contained in a ‘normal diet’ is absorbed and this drops to about 10 per cent in a vegetarian diet. Thus, vegetarians need to consume up to 80% more iron in their diet to achieve the same intake of iron as non-vegetarians. (A list of foods containing significant amounts of iron appears below.)
An important point to remember is that unidentified blood loss can be a cause for iron-deficiency anaemia and that such blood loss can come from an undetected cancer, especially one in the bowel or stomach. In people with iron-deficiency anaemia, especially older individuals, it is very important that such causes are excluded by medical investigations.
Increasing dietary iron intake is unlikely to provide adequate iron to treat established iron deficiency and oral iron supplements are required. The usual dose is 200mg of elemental iron per day for adults. This is equivalent to about 600mg of modified released ferrous sulphate. (This is the elemental iron-containing compound found in most iron tablets.) Many adult iron preparations available in Australia for adults do not contain enough iron. The dose for children varies according to their body weight. (The child's medical practitioner can advise re the correct dose.) Iron tablets are best taken on an empty stomach (30 to 60 minutes before a meal or two hours after).
Children with iron deficiency should imit their cow's milk intake as it reduces iron absorption and can cause irritation of the bowel that leads to smal amounts of blood loss and thus further iron loss.
Major foods contributing to iron and zinc intake |
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Foods high in iron |
Foods high in zinc |
|
Haem |
Non-haem |
|
Liver, lamb’s fry |
Tofu |
Oyster, raw |
Factors affecting iron absorption from the diet |
|
Increase iron absorption |
Decrease in iron absorption |
The consumption of meat protein (including red meat, fish and chicken) |
Tannins in tea (It is fine to consume tea away from the main meal.) |
Leafy green vegetables (haem iron foods) |
Phylates in cereals |
An acid pH (improved by consuming citric and lactic acids) |
Antacid use |
Vitamin C (non-haem iron foods) |
Phenols in red wine |
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Calcuim has a minor effect but should not be avoided as it is far more likely to be taken in insufficient quantity. |
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Phosphates in eggs |
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Iodine – Especially important for women and children
Iodine is another mineral that may be mildly deficient in a significant proportion of the population. Iodine is needed for the production of thyroid hormones and severe deficiency causes hypothyroidism (an under-active thyroid) and often an enlarged thyroid gland (a ‘goitre’). In fetuses and young babies this can lead to significant problems in speech, movement, hearing and intelligence. Interestingly, taking a large excess of iodine (via supplements) can also cause hypothyroidism. This can be a real problem if a pregnant woman takes such supplements as they easily cross the placenta.
Until recently, iodine deficiency was only a problem in some areas of Tasmania that were naturally deficient. However, iodine deficiency has become an Australia-wide issue in the past few years due to a change in the iodine content of milk, with a recent study finding that school children in NSW and Victoria are mildly deficient and those in SA borderline. Milk products used to provide much of our iodine requirement. This iodine came not from the milk itself but from incidental ‘contamination’ of the milk with iodine-containing detergents used for cleaning milk vats. The use of these products ceased some years ago, which resulted in the iodine content of milk dropping by about two thirds. This drop has meant that many Australians have now a mildly inadequate intake of iodine. One solution to this problem would be the use of iodised salt in bread and it is thought that this action would provide enough iodine to overcome a mild deficiency; although obviously only in those who eat supplemented bread. Such a supplementation is being assessed at present by health authorities.
In the mean time, the best dietary sources of iodine are seaweeds (an excellent source, e.g. sushi and nori rolls), milk products and seafood, with lesser amounts in eggs, vegetables, fruit (especially citrus), cereals and nuts (especially cashews). Normal salt is not helpful as has very little iodine. The levels of iodine in these products vary greatly depending on the natural levels present in soils, plants etc.
Iodine - Especially important for pregnant women
The normal daily requirement of iodine is 120micrograms in children and women, 150 micograms in males, 170 micrograms in pregnant women and 200 micrograms in lactating women. The higher requirements for pregnant and lactating women mean that foetuses and young babies are more at risk of iodine deficiency and some specialists recommend that pregnant and lactating women should take iodine supplements in doses of 100 to 200 micrograms per day. As stated above, it is very important not to take excessive amounts of iodine when pregnant or lactating; 100micrograms is fine. Such supplements are quite safe for normal women. However, women who already have thyroid problems need to discuss supplementation with their doctor.) An alternative is to eat more dairy products, seafood and seaweed. Infants who are not breast fed need diary products to ensure an adequate supply of iodine.
Magnesium
Deficiencies can occur in chronic alcoholism and in association with some medications, such as some diuretics. Determining whether a deficiency exists is difficult as blood tests measuring magnesium may not give an accurate (and thus useful) indication of body magnesium status. Supplements should not be taken unless a deficiency has been proven and they should only be prescribed by a doctor as they can cause diarrhoea and can be toxic, especially in the elderly. Many foods are good sources of magnesium, including green vegetables, nuts, legumes, wheat germ and wholemeal bread, and most people can easily obtain adequate magnesium from their diet.
Vitamin supplements
Uses of vitamin supplements
All vitamins and minerals have been the subject of extensive study. The daily recommended intakes for vitamins and minerals that are advised by health authorities are based on all the well researched information available. There is no reason for them not to be! They are therefore the most reliable guide to vitamin and mineral intake. Those wishing to find out more about individual vitamins and minerals can do so by accessing the National Health and Medical Research Council’s recent (September 2005) and very comprehensive publication on this topic; Nutrient reference Values for Australia and New Zealand including recommended dietary intakes. (It is available free on their web site at: www.nhmrc.gov.au/publications/synopses/n35syn.htm
These recommended levels can be maintained in most people by adhering to their usual varied diet. Despite this, many Australians continue to purchase vitamins that are of no benefit. Some common reasons for this practice are as follows.
- Many Australians believe they eat very poorly and that they are likely to be deficient in vitamins etc. The truth is that our dietary problems are due to having too much food, especially fat and sugar. As stated above, vitamin and mineral deficiencies are rare in Australians.
- Some people believe that present day foods are poorer in quality and have less nutritional value. There is no evidence that this is the case.
- People often feel their stress and tiredness are due to a nutritional deficiency of some kind. This is rarely the case, although people who are chronically tired should have their iron levels checked, especially women with heavy menstrual periods.
- Many people seem to believe that vitamins have magical properties that will prevent a multitude of diseases. Thus, they often take the attitude that ‘if some is good, more is better’ and feel that any increase in their vitamin intake is beneficial, or at least can’t hurt. This is not true and there are some vitamins that are toxic to the body if taken in excess. This is especially the case with fat soluble vitamins (vitamins A, D, E and K) which can be stored in the body in large quantities. Special care needs to be taken to avoid toxic doses of vitamin A (retinol), which in excess has been associated with an increase in hip fractures. (Also, high doses of beta-carotene (a precursor of vitamin A) causes an increases in lung cancer in smokers.)
- The placebo effect (see above) means that people often feel better when taking supplements even thought the supplement had no effect at all.
There are better things to spend hard earned money on!!
There are, however, some situations in Australia where micronutrients are deficient. This can occur either because the nutrient is generally marginally deficient in the diets of most Australians or because a particular type of diet is deficient in a particular nutrient(s). In these cases supplements may be needed but it is best to discuss which supplements are needed with a GP or dietitian.
1. Specific deficiencies that effect the population generally.
These are discussed below or in other parts of this book.
- Folate: Folate supplements for women of child bearing age. These should be taken by any woman who has any likelihood of becoming pregnant as supplements have been shown to significantly reduce the risk of neural tube defects, a group of serious abnormalities that occur early in the life of the developing foetus. To be helpful, the woman needs to be on them when she becomes pregnant. (See section on 'Dietary, drug and medication issues in pregnancy')
- Calcium: Calcium supplements in those with a low calcium intake, particularly in post-menopausal women. (See section on osteoporosis.)
- Iron: Iron intake in women (and men) with diagnosed (by blood tests) iron deficiency and no other underlying cause, such as blood loss from a cancer. (See section above on 'Iron deficiency')
- Iodine (See section above on 'Iodine deficiency')
- Zinc (See table above detailing 'Zinc rich foods')
- Magnesium (See section above on 'Magnesium deficiency')
2. Specific population groups who are likely to have deficient intake of minerals and vitamins and require a multi-vitamin / mineral supplement.
- Frail aged people (See section on 'Malnutrition in the elderly')
- Some vegetarians (See section below on 'Vegetarian diets')
- People with multiple food allergies or intolerances (See section on 'Food allergies')
- People who chronically abuse alcohol who are likely to be deficient in vitamins (especially vitamin B1).
- People with diseases affecting their bowel that reduce their ability to absorb vitamins and minerals from their diet. Such diseases are relatively uncommon and beyond the scope of this resource.
- People with inadequate diet due to poverty or bizarre eating habits.
The vitamin message
Don’t assume a vitamin deficiency is the cause of a health problem as it may result in missing / delaying making the real diagnosis and wasting money on unnecessary supplements. People who are worried about their diet or have a problem should talk to their GP about their concerns. He or she can advise about proper nutrition and help find the cause of any underlying condition, should one be present. People who still feel they need to take supplements should do so for as little time as possible and take a supplement that has a wide range of vitamins etc in concentrations that do not exceed the recommended daily allowance for each compound. Also, ensure that purchased vitamins are produced in Australia by reputable companies.
Antioxidants
The oxidation of body tissues and compounds is a damaging process that is continually being fought by the body. It is principally caused by unstable compounds called free radicals. Free radicals are unstable because they lack an electron in their structure. In order to become stable, they steal electrons from other compounds they come in contact with. The loss of this electron is a process termed oxidation and the resultant changes in the structure of the oxidised compound often disrupt its ability to function properly in the body.
Free radicals are produced by normal chemical reactions in the body, a process that can be increased in conditions such as diabetes and perhaps stress. Many different types of free radicals can also be ingested, a principle culprit being tobacco smoke. Others include alcohol, animal fats, smoked and char-grilled foods, oils heated during deep-frying and pollutants. Oxidation by these free radicals can affect blood lipids, the immune system, DNA (genes), enzymes, hormones, skin proteins etc. All this can lead to an increase in many diseases, including cardiovascular disease, cancers, and inflammatory diseases, such as arthritis.
As well as being fought by the body, oxidation reactions caused by free radicals can be prevented or reversed by antioxidants consumed in the diet. These are substances that have an extra electron that they can give away. There are two main groups of antioxidants; nutrients which play essential roles in processes in the body, such as vitamins C, E & beta-carotene, and various other compounds found in foods, including carotenoids, polyphenols, flavenoids, catechins & theaflavins (in tea). Hundreds of different antioxidants are present in vegetables, fruit, wholegrains, olive oil, nuts, tea, soybeans, dark grape juice and red wine, and many more are still being identified. Knowledge about which antioxidants are most beneficial is very limited at present and it is therefore advisable to have as wide a range of antioxidant-containing foods as possible.
Antioxidant and vitamin supplements for heart disease and cancer prevention
It is thought that antioxidants consumed via a normal diet do help prevent coronary artery disease (heart disease) and this has led to many people taking supplements of ‘antioxidant’ vitamins in the belief that they will also help reduce heart disease. There is now good evidence that, unlike antioxidants in food, these antioxidant supplements provide little or no benefit with respect to heart disease. Similarly, the protection against cancer that is provided so well by nutrients in vegetables and fruit cannot be replaced by supplements. In fact, taking large doses of only a few antioxidants has been shown to be harmful in some studies.
The reason that taking antioxidant supplements is unlikely to be of benefit is that there are hundreds of different antioxidants present in foods and we are likely to need a wide range of them for good protection. Also, as we don’t know which are most beneficial or in what dose, it is not possible to know which antioxidants should be included in supplements. Antioxidant supplements just cannot supply the hundreds of nutrients found in normal food. Until a great deal more is known about this topic, taking supplements for cancer or heart disease prevention is most likely going to be a waste of money and may even cause harm.
Vegetarian Diets
Vegetarian diets are generally a healthy option, especially if milk products and eggs are allowed in the diet. It is also an increasingly common option, especialy amongst adolescent girls. About 25 per cent of girls choose to be vegetarian at some stage during their teenage years. Whilst some take this option for moral reasons, many do so to lose weight. Luckily, most remain quite well with the incidence of anorexia being about one per cent.
Animal products provide protein, energy and fat. As most Australians take excess fat and energy, the reduction in these that results from a vegetarian diet is often beneficial. However, some vegetarians have an energy deficient diet and are underweight and unhealthy. As egg whites and milk products are rich in good protein, a vegetarian diet that includes these and a good variety of plant proteins is usually not protein deficient. Sources of plant proteins include cereals, nuts and legumes, such as soy beans, lentils, beans and peas.
Vegetarians who choose not to consume milk products and eggs need to be more careful to ensure their protein intake is adequate, both in the total amount and in the types of aminoacids that are present in the protein. (Amino acids are the building blocks of all proteins. Some, called essential amino acids, can not be made by the body and must be obtained in the diet.) Total protein intake needs to be at least 0.7g per kilogram of body weight each day in adults and 1.0g per kilogram of body weight per day in the elderly. A mix of 70 per cent from cereals and 30 per cent from legumes is ideal. Nuts should also be included each day. These foods neeed to be a large part of the diet to ensure adequate protein and energy requirements. Vegetarians who do not consume milk products or calcium enriched foods, such as calcium enriched soy products, will need calcium supplements.
Vegetarian diets without milk products and eggs often provide inadequate levels of vitamin B12. (As body stores of vitamin B12 are large, a deficiency may not appear for several years after adoption of the diet.) Vitamin B12 deficiency also affects the unborn children of affected mothers causing neurological problems and women of child bearing age on this diet should take supplements of vitamin B12. This issue should be discussed with a medical practitioner. Vegetarian diets without milk products and eggs are not suitable for children.
Iron can be deficient in some vegetarians and those requiring extra iron, especially teenage girls and pregnant women, may require iron supplements if they have been shown to be iron deficient by a blood test. (A list of foods high in iron appears below in section on vitamins and menerals.)
Hints for preserving nutrients in vegetables and fruitStart with fresh vegetables and herbs whenever possible and try not to not store fresh foods for long periods (a week at most). Fresh fruit and vegetables are still alive when bought and continue to respire; breathe in oxygen and breathe out carbon dioxide and water vapour. This process is necessary for the food to stay healthy and requires oxygen. Thus, don't seal them in an airtight container. A cold environment (putting them in the fridge) slows this process down. Whether you want to slow this process down or not depends on the type of fruit / vegetable. Storing food in the fridge
Foods that should not be stored in the fridge
Cooking food
Finally, fruit and vegetables are one of the largest causes of food waste, with the average household throws away about $2,000 worth of fruit and vegetables each year. Doing the above will save you money. |
Hints for preserving protective nutrients in vegetables and fruit
Start with fresh vegetables and herbs whenever possible and try not to not store fresh foods for long periods (a week at most).
Fresh fruit and vegetables are still alive when bought and continue to respire; breathe in oxygen and breathe out carbon dioxide and water vapour. This process is necessary for the food to stay healthy and requires oxygen. Thus, don't seal them in an airtight container. A cold environment (putting them in the fridge) slows this process down. Whether you want to slow this process down or not depends on the type of fruit / vegetable.
Storing food in the fridge
- Foods that should be stored in the fridge include leafy salad vegetables, asparagus, broccoli, capsicums, cucumbers, beans, mushrooms, carrots and fruit that is already sweet and won't get sweeter with ageing, such as berries and citrus fruit.
- Put them in the fridge as soon as you get home and don't leave them in the car in the heat for long periods on the way home.
- Fruit and vegetables stay crisper in a humid environment, as provided in your fridge crisper, and this is improved by keeping them in a plastic bag (but not an airtight one). (An exception is cuccumbers which last longer if the are tightly wrapped in plastic. Some can be bought like this.)
- Too much moisture is also harmful as as the extra moisture encourages the growth of micro-organisms and thus causes food to rot quicker. It is therefore best to avoid washing fruit and vegetables until they are about to be eaten. (If you use lettuce spinners make sure most of the water is removed. Lots of spinning.) Also, remember that fruit and vegetables produce moisture as they age and this can add to the problem if there is inadequate ventilation.
- Special plactic containers that have vents and a raised shelf on the bottom are ideal as they keep food moist, avoid the problem of sitting in a puddle of water on the bottom and allow oxygen entry.
- Beans and cuccumbers like warmer parts of the fridge and tend to go off more quickly. They should be eaten soon after purchase.
- Carrots tend to lose water quickly and should be kept in a container in the fridge.
- Mushrooms are praticularly susceptible to rot from exposure to excess water. Storing them in a paper bag prevents rot occurring and putting that paper bag in an open plastic bag prevents the mushrooms drying out.
Foods that should not be stored in the fridge
- Some foods need to soften and go sweet (ripen) before eating and the cool fridge slows this process. Thus, these foods should be kept in a bowl and in a cool shaded place. They include tropical fruits, stone fruit, pears, apples, kiwifruit, tomatoes and avocadoes. These fruits also emit a gas (ethylene) that can cause a bitter taste in carrots and increase the ripening of foods in the fridge; something you are trying to slow down. (If you do want to speed up the ripenning of avocadoes and tomatoes, put them in a fruit bowl with 'ethylene emitting' ripening bananas.)
- Tropical fruits such as mangoes, banans and pineapples are sensitive to chill injury and are best kept in a bowl.
- Potatoes,, onions and garlic should be kept out of the fridge as the humidity will make them sprout. They should not be kept in a plastic bag. Potatoes need to be kept in a dark place as light exposure makes the go toxic. A potato that is green is likely to be toxic and should not be eaten. (This process does not occur in sweet potatoes.)
Cooking food
- Keep pieces as large as possible when chopping/slicing.
- Water soluble vitamins are the ones that are destroyed by cooking / lost by dissolving into cooking water. Maximum losses during cooking vary from 10 per cent for vitamin B12 to 100 per cent for more unstable vitamins, such as folate and vitamin C. Fat soluble vitamins are more hardy and don’t dissolve in cooking water.
- When cooking vegetables, minimise both cooking time and cooking water to reduce vitamin losses. Vitamin losses with cooking vary from about 10% with steaming or micro-waving to about 50% with boiling. Most of the vitamins lost are the water soluble ones. The preferred cooking method for reducing vitamin loss is micro-waving (with little water), followed by steaming, stir-frying and lastly, boiling. If boiling, add food only when the water is boiling and boil in the smallest amount of water possible. Do not soak vegetables before cooking.
- Do not use copper pots or utensils as they can increase losses of some vitamins, particularly vitamin C.
- Use cooking water and liquid from canned foods in sauces, gravies etc.
- Do not use baking powder to preserve vegetable colour during cooking as it increases vitamin losses.
- Heating is not always bad. While heating tomatoes decreases its vitamin C content, it increases the availability of antioxidants including lycopene.
Finally, fruit and vegetables are one of the largest causes of food waste, with the average household throws away about $2,000 worth of fruit and vegetables each year. Doing the above will save you money.
Juice bar drinks
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What is a healthy diet?
There are many nutritional factors that require consideration in formulating a healthy diet and these will be discussed in the rest of this section. Below is a table summarising what most nutritionists and dietitians would consider a healthy diet.
Recommended food intake for a healthy diet low in fat
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Bread, pasta, potatoes (prepared without fat), grains
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Meat, fish, chicken, eggs, legumes: Meat must be lean with all visible fat removed and chicken should be skinless.
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Vegetables
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Fruit
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Nuts
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Milk products
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Fats and oils
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Indulgences
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Fluids
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