Nutritional Requirements

Individual nutritional requirements are determined by age ,gender, environment, genetic and isoenzyme constitution. The amount of intake for energy must be sufficient for childhood growth and adult work, leisure activities, pregnancy and lactation. The needs for a growing child who is physically active and laying down a wide range of tissue types, neural including brain, muscle, enzyme systems, liver tissue, bone and connective tissue, are in contrast to the mature exercising young adult in the physical prime of life. The pregnant or lactating woman’s needs will be of a different qualitative and quantitative nature. The teenage mother who is growing as well as sustaining a growing infant has added needs. As the person ages the body requires much more care and maintenance as all activities reduce in intensity. The energy requirements of the elderly fall but the nutrient requirement remains. The requirement for nutrients, i.e. essential constituents of the diet may remain unchanged during these activities.

The concepts of an energy dense and nutrient dense diet is important.

Requirements are also altered by stress, illness, smoking and trauma, and these needs are met, dependent upon the financial status of the person and community. Adequate nutrition cannot be assumed because there are no obvious clinical features of deficiency disease. Indeed some degree of malnutrition has been identified in a significant proportion of the hospital populations of affluent countries.

Optimal dietary requirements are those dietary intakes of nutrients which are most likely to ensure that the individual will attain optimum potential nutritional status for :

  • Successful development in utero
  • growth
  • learning potential
  • quality of life
  • body function
  • successful pregnancies
  • adequate milk production for the baby’s needs
  • expectation of a long and healthy life
  • freedom from infection
  • resistance to disease and response to diseases

Appropriate nutrition requires that all nutrients, carbohydrates, lipids, proteins, minerals, vitamins and water are taken in adequate amounts and in the correct proportions. This is essential for normal organ development and function, reproduction, repair of body tissues and combating stress and disease. Many nutrients require the presence of other nutrients if they are to fulfil their activity within the body.

There are levels of requirements for a nutrient. The amount recommended will always exceed the precise needs because of the inefficiency of the biological processes:

Basal requirement is that which is required to protect against clinical impairment of function due to insufficient intake.

Storage requirement allows the body to maintain body tissues reserves. The reserve provides a supply of nutrient which can be mobilised without detectable impairment of function.

Level to maximise health and improve quality of life

Level to avoid chronic disease

Nutritional requirements meet

Fixed energy expenditure i.e. basal metabolic requirements e.g. breathing , cardiac output, intestinal peristalsis

Variable energy expenditure ie growth, movement ( exercise, eating and drinking , exercise and work on heat production , digestion, breathing, cardiac output , renal function, nervous system during active periods. Also pregnancy and lactation

The variable energy output of the child and young mother is enormous, and therefor the ratio of Fixed to Variable energy expenditure is high. In contrast the energy expenditure of the declining elderly person is much smaller and consequently the Fixed to Variable energy expenditure ratio is small.

Nutritionists must make recommendations based on scientifically generated facts giving guidelines for groups and individuals in the community. The definition of dietary requirements is very exacting. The important question is: requirement for what? An example of the complexity facing the scientific committees is giving recommendations for the daily requirements for folic acid (200?g /day) . There are two groups where the recommended intake is double at 400?g /day the recommended intake for the population. One group is women contemplating pregnancy and who wish to minimise the risks of neural tube defects. Another group of adults need to reduce the plasma homocysteine concentration to reduce the risk of coronary heart disease. An intake of 400 ?g /day of folic acid is only achievable by fortified foods or supplementation in tablet form and is not possible by unfortified foods alone.

The fulfilment of nutritional needs is dependent upon agricultural economic effectiveness, particularly in developing countries. The recognition of this basic premise has been essential for the survival of every major civilisation. The development of farming as an industry means that the whole process of food production, which is central to the health of a community, requires supervision by agencies independent of but reporting to parliament or government . Examples are the Food Standards Agency in the UK, Agence Francaise de Securite Sanitaire des Aliments in France and the Food and Drug Agency (FDA ) in the United State of America. References terms relating to energy and nutrient intakes :

AI, Adequate Intake. If the scientific evidence is insufficient to establish a requirement , then a figure for AI is obtained from the best available information

Basal requirement: The dietary requirement of a nutrient to prevent any clinically demonstrable impairment of function. Defined by FAO/WHO.

DRI : Daily Reference Intakes , ( USA, Canada , 2000 ) a collective name which refers to four nutrient based reference values, EAR, RDA, AI, UL.

DRV: (UK 1991) Dietary Reference Value; a term used to cover LRNI, EAR, RNI and safe intake

DV: Daily Values, ( USA ), single figures created by the US Food and Drug Administration. A term used in UAS nutrition labelling for a reference intake level. Two types of reference intake are defined, RDI ( Reference Dietary Intake ) for minerals and vitamins and DRV ( Daily Reference Value ) for certain other nutrients).

EAR: Estimated Average Requirement for a group of people for energy, protein, vitamins or minerals.

LRNI: Lower Reference Nutrient Intake for protein, vitamins or minerals. An amount of the nutrient that is enough for only a few people in a group who have low needs.

Normative storage requirements : the dietary requirement of a nutrient to maintain a reserve in body tissues.

RDA: Recommended Daily Allowances (USA 1941). The level of intake of essential nutrients considered to meet the functional needs of practically all healthy persons Statistically this intake would prevent deficiency disorders in 97% of the population. The term was devised to allow modification with changing knowledge and was not intended to imply a minimum or optimal requirement. Superseded by Dietary Values.

RDA: Recommended Daily Amounts (United Kingdom, 1979). The average amount of the nutrient which should be provided in a group of people if the needs of practically all members of the group were to be met. These are averages for the group not amounts which individuals must eat. Superseded by RNI in UK, but European RDA s are used in food labelling.

RDI: Recommended Daily Intake of nutrients for the United Kingdom, (1969). The recommendation applies to food as actually eaten.

RNI: ( UK 1991 ). Reference Nutrient Intake for protein, vitamins or minerals. An amount of the nutrient that is enough or more than enough for about 97% in a group. If the average intake of a group is the RNI, then the risk of a deficiency in the group is extremely small. The value is equivalent to RDA or RDI.

Reference values for nutrient intake. ( German speaking countries 2000). Nutrient intakes which meets the demands of 97.5% of a population group and for evaluation of the nutrient supply of the population.

Safe intake: The term used to indicate intake or range of intakes of a nutrient for which there is not enough information to estimate RNI, EAR or LRNI. It is an amount which is enough for almost everyone, but not so large as to cause undesirable effects. An upper limit of safe intake is not however implied by this recommendation.

UL (USA) Tolerable upper limit, is the highest amount of nutrient intake unlikely to pose any risk of adverse health effects to almost all individuals in the general population.

USRDA Recommended Daily Allowances. (USA 1968). A selection of the highest values for 20 nutrients from the RDA s and used as standards for labelling. . The requirement for a nutrient varies from one person to another, and may alter with the composition and nature of the diet as a whole. There is no absolute requirement for fat, sugars or starches, though there are for essential fatty acids, vitamins and minerals. Estimates of requirements may be made from:

  • the intake of a nutrient by individuals or by groups which is associated with the absence of any signs of deficiency disease
  • the intake of a nutrient to maintain a given circulating concentration or degree of enzyme saturation or tissue concentration
  • the intake of a nutrient needed to maintain balance, noting that the period over which such balance needs to be measured differs for different nutrients and between individuals
  • the intakes of a nutrient needed to cure clinical signs of deficiency
  • the intake of a nutrient associated with an appropriate biological marker of functional nutritional adequacy

Infants: The baby’s nutritional needs are adequately provided for by its mothers milk until 4 months. WHO recommends exclusive breast feeding for about six months. Iron and iodine provided in breast milk though not adequate would not require supplementation. Thereafter the increasing nutritional demands of growth require the introduction of weaning to solid food.

Children 1-3 years. Essential nutrients and the great energy expenditure and growth needs of the toddler require to be provided by the diet.

Children 4-10 years. Energy and protein, vitamins and minerals intake must meet the demands of activity and growth.

Children 11-18 years. Energy and protein needs continue to increase particularly for boys, who require increased intakes of vitamins and minerals. Once menstruation begins there are increased requirements for iron.

Adults 19-50 years. Growth is completed and also the frenetic activity of the young is over. Energy requirements are reduced though the requirements for protein and most vitamins and minerals remain the same.

Pregnancy. The most important requirement is for folic acid supplementation before and in early pregnancy. There is increased requirement for some but not all nutrients to provide for the energy needs associated with the growing foetus.

Lactation. The energy demands of milk production are reflected in increased dietary requirements of protein , minerals and vitamins if maternal good health is to be maintained.

50+ years. The elderly are less energetic and protein requirement is less in men though maintained in women. After the menopause the female requirement for iron is the same as the male. Vitamin and mineral demands are unchanged except for increased vitamin D after the age of 65.

Nutritional requirements for energy

The energy requirement of an individual is the energy intake of food which will support energy expenditure requirements in that individual who requires economically and socially desirable physical activity consistent with body size, composition and long-term good health.

Energy is not a nutrient but is released from the carbohydrates, fat, protein and alcohol in food, and is therefore a composite term. Energy requirements are very individual and variable and dependent upon metabolic processes, physiological functions, muscle activity, heat production , growth and synthesis of new tissue. That is energy for immediate use or in industrial terms just on time energy.

There are few methods available to measure energy status, though a constant weight or a Body Mass Index of 20-25 are reasonable guides. The energy requirements in healthy people could be defined as the food energy to maintain a predetermined BMI and physical activity. In endurance athletes the glycogen content of muscle gives a clue to stamina..

Involuntary energy expenditure consists of different components

  • Resting metabolism ; the energy costs of the normal metabolic processes of the body
  • Adaptive involuntary energy expenditure to cope with cold conditions.
  • Energy associated with absorbing and metabolising food.

The Harris-Benedict equation is used to measure basal Energy Expenditure. It is important that the equation is used as originally designed in 1919. The temptation is to round off the long decimal places, which introduces errors of between 7 and 55% depending on the particular figures rounded off.

For men, the Basal Energy Expenditure. =
66.4730 + (13.7516 x weight in kg) + (5.0033 x height in cm) – (6.7750 x age in years)

For women, the Basal Energy Expenditure =
655.0955 + (9.5634 x weight in kg) + (1.8496 x height in cm) – (4.6756 x age in years)

Total Caloric Requirements = Basal Energy Expenditure x the sum of the stress and activity factors.

The metabolic energy content of a foodstuff is a measure of the proportion of the ingested food which appears to be available for metabolism in the body. Only after absorption does the nutrient with the exception of proteins, attain full value.

Dietary energy is the estimated average requirements (EAR) for different age and gender groups. EAR for energy reflects estimates based on Total Energy Expenditure (TEE) . Total Energy Expenditure is calculated by multiplying the Basal Metabolic Rate (BMR) by Physical Activity Level (PAL).


Basal Metabolic Rate is the rate at which the body uses energy when the body is at complete rest. Values depend on age, sex and body weight. For a 65 kg man BMR is approximately 7.56 MJ/day. For a 55 kg woman, BMR is about 5.98 MJ/day.

The physical activity level is the ratio of overall daily energy expenditure to BMR. A PAL of 1.9 would reflect a very active work pattern. The physical activity level of 1.4 is a minimum of activity at work and leisure. A physical activity level of 1.5 should be used for individuals aged 60 years. Old people have low levels of energy expenditure and dietary intake with a consequent risk of nutritional deficiency.

In the 1985 report of the FAO/WHO/UNO Expert Consultation Committee the maintenance energy needs were calculated as 1.4 × BMR for both men and women while the other components are expressed as a function of BMR. The average daily requirements of an elderly person might be approximately 1.55–1.75 × BMR.

The energy intake in excess of these requirements is stored as fat until needed. The energy intake should meet just on time requirements.

See Appendix for UK and Australian nutrient recommendations.

Dietary planning and guidelines.

No matter how carefully dietary guidelines are constructed the requirement at the end of the day is to ensure that the population is able to understand the thinking behind the scientific recommendations and that the recommendations be translated into recipes for delicious food and pleasurable meals. ( Appendix 1 )


There are now many Agencies , local, National, European Community and FAO and World Health Organisation which have made great efforts to define nutrient recommendations for their populations. The task of the FAO and WHO is particularly demanding because of the range of communities served. From the poverty stricken in frozen , temperate and tropical countries to the affluent and well fed.

Dietary guidelines are also written by Government Agencies and Associations interested in preventing and coping with specific diseases e.g. heart disease or cancer. They aim to provide a diet which may, in their opinion, minimises the chance of acquiring such a disease.

Recommendations vary from country to country, but the general theme is:

  • enjoy your food
  • eat a nutritionally adequate diet drawn from a variety of foods
  • reduce the consumption of fat, especially saturated fat ( total fat to 30-35 % of daily calories)
  1. 8-10% of total calories from saturated fatty acids,
  2. up to 10% of total calories from polyunsaturated fatty acids
  3. up to 15% of total calories from monounsaturated fatty acids
  • achieve and maintain an appropriate body weight
  • increase the consumption of complex carbohydrates and dietary fibre
  • reduce the intake of sodium ( less than 6 g/day)
  • consume alcohol in moderation, not more than 2 drinks/day. Children and pregnant women abstain.
  • That carbohydrates should provide 55-60% of the daily energy intake, a high proportion of which should be fruit, vegetables and whole wheat products. (This figure is for meat and fish eaters and will be quite different for vegetarians.)

1. Adequate nutrition requires that all nutrients, carbohydrates, lipids, proteins, minerals, vitamins and water are eaten in sufficient amounts for normal organ development and function, reproduction, repair of body tissues and combating stress and disease. The nutrient energy intake should be appropriate for sustained activity and effective physical work.

2. Dietary reference values for food energy and nutrients include BMR (Basal Metabolic Rate), PAL (Physical Activity Level) and PAR (Physical Activity Ratio). Terms relating to energy and nutrient intakes include and have included RDI (Recommended Daily Intake), RDA (Recommended Daily Amounts) of food energy and nutrients, EAR (Estimated Average Requirement) for a group of people, LRNI (Lower Reference Nutrient Intake), RNI (Reference Nutrient Intake) for protein, vitamins or minerals, Safe Intake and DRV (Dietary Reference Value).

3. Dietary guidelines interpret these into practical statements, for real-life nutrition. Recommended nutrient and dietary allowances indicate the requirements of individual nutrients for defined population groups, e.g. babies, toddlers, pregnant and lactating women. Nutritional and dietary guidelines recommend intakes of food, milk, meat and vegetables, etc.

4. The energy requirement of an individual is the level of energy uptake for food which will balance energy expenditure when the individual has a body size and composition and level of physical activity consistent with long-term good health, and allow for economically necessary and socially desirable physical activity. In women who are pregnant or lactating, the energy requirement includes the deposition of tissue or the secretion of milk at rates consistent with good health.

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dietary guidelines around the world.
US dietary guidelines
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a risk assessment model for establishing upper intake levels for nutrients .
South African Journal of Clinical Nutrition
Good discussion on US nutrition standards and guidelines


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