Nutrients and dietary guidelines

Nutrients are food components that are required for optimal growth, development and body function. Macronutrients (protein, fat and carbohydrate) are the basic building blocks for energy, lipid and nitrogen components of the body, and are essential for cellular homeostasis. Micronutrients (vitamins, minerals and trace elements) are required in much smaller amounts. Individual nutrient requirements vary with age, size, growth and health status.

In 2003, the Australian National Health and Medical Research Council (NHMRC) released a document that includes ‘Dietary Guidelines for Children and Adolescents in Australia’ (available at: http://www.nhmrc.gov.au/_files_nhmrc/file/publications/synopses/n31.pdf). These guidelines provide complete nutritional advice for healthy children from birth to 18 years of age. They have been updated and will be available from 2011 on the website www.nhmrc.gov.au.

Energy

Food is metabolized and provides energy required by the body for growth and synthesis of new tissue, for metabolic processes, and for physiological functions and activity.

Fat, carbohydrate and protein provide energy, which is measured in kilojoules (kJ) or kilocalories (1 kcal provides 4.182 kJ). Fat provides a concentrated source of energy, contributing 37 kJ/g, approximately twice that provided by an equivalent amount of protein or carbohydrate. Fat contributes 50% of the total energy in breast milk or standard infant formula. The average diet of older children provides 30–40% of total energy from fat, 45–55% from carbohydrate and about 15% from protein. Most of the energy intake in children is used for growth and development. Recommendations for energy intake are difficult to determine, even for individuals of similar age, sex and size, because requirements vary. The NHMRC recommends that for children aged 5–14 years approximately 30% of energy intake should be fat, with no more than 10% coming from saturated fat.

Dietary assessment

The primary care giver(s) should be asked what the child usually eats in a typical day, in all settings that the child is in (i.e. home, child care, outings). Children derive up to 30% of their energy from snacks, so it is important to include these in the assessment of all food and fluids consumed.

Qualitative methods include a dietary history and food frequency questionnaire. These do not allow for the precise calculation of energy or nutrient intakes but rather determine the pattern, style and types of foods eaten.

Quantitative methods calculate precise energy and nutrient intakes and include a 24-hour food record and a 3-day food record.

If the initial dietary assessment raises concerns, referral should be made to a dietitian.

Physical examination and anthropometry

Physical examination gives a general impression of nutritional status, including signs of anaemia, jaundice, wasting, oedema, lethargy, muscle weakness and fat stores.

Examination may reveal evidence of specific micronutrient deficiency, including pallor, bruising or bleeding, skin, hair and gum abnormalities, and neurological or ophthalmological disorders. In adolescents, the stage of puberty should be documented.

Anthropometry refers to the measurement of physical dimensions and body composition. Measurement of height/length and weight gives the most useful assessment of overall nutritional status, although normal growth can still occur in marginally malnourished children. Serial measurements of growth add valuable information about the impact and chronicity of nutritional compromise. The following routine measurements are used:

Growth charts for height or length, weight and head circumference are used to monitor growth at different chronological ages (see Chapter 19.1). Specific ethnocultural and syndrome-specific (Down, Turner) growth charts exist. Intrauterine growth curves have been developed for gestational ages 26–42 weeks using birth weight and length data for infants born at successive weeks of gestation. Premature infants should have the weight corrected until the child is 24 months of age, length until the child is 36 months of age, and head circumference until the child is 18 months of age.

Patients requiring long-term monitoring of nutritional status should have serial measurements of mid-arm circumference and triceps skinfold thickness to assess fat and muscle stores.

Body mass index

Serial body mass index (BMI) is used as a representative measure of body fatness in children (see Chapter 3.4). It cannot, however, distinguish between excess weight produced by adiposity, muscularity or oedema. In children with nutritional deficiency, and in the setting of overweight and obesity, it is a useful measure of adiposity. It is calculated from the formula BMI  =  weight [kg]/height [m]². A BMI greater than the 85th percentile is defined as overweight and a BMI greater than the 95th percentile as obesity.

Laboratory assessment

Laboratory assessment is used to detect subclinical deficiency states or to confirm a clinical diagnosis. It provides an objective means of assessing nutritional status. Laboratory assessment is summarized in Table 3.3.1.

Table 3.3.1 Laboratory parameters for assessing nutritional status

Breastfeeding initiation

Information about the advantages and management of breastfeeding, including where to obtain advice and support, if needed, should be made available to all new mothers. Reasons given by mothers for stopping breastfeeding include pain and discomfort (e.g. sore nipples, mastitis, thrush), anxiety regarding the adequacy of milk supply, and a return to work.

Common problems with breastfeeding

Problems may exist with both maternal breastfeeding technique and anatomy, as well as with the infant’s suck and oropharyngeal anatomy. In addition, insufficient milk supply is often perceived to be a major problem, which may lead to unnecessary cessation of breastfeeding. Most women are physiologically able to produce sufficient milk. Appropriate education, encouragement and support may be all that is needed.

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