Topic 3: Infancy

Question 1

What are the three concepts involved with infant nutrition?

Answer 1

• Digestion: Infants are born with the ability to digest and absorb nutrients from human milk or formula. The digestive system matures during infancy so that a wide variety of foods can be used by the end of the first year.
• Growth: Individual energy and nutrient needs reflect rapid growth demands for fuel, building materials and basal metabolism.
• Development: Infant feeding behaviour follows a defined developmental sequence. Maturing oral structures and function determine developing infant eating skills and appropriate textures of food.

Question 2

What are the three physiological characteristics that influence the dietary requirements of an infant?

Answer 2

• small body size
• immature physiological functions and
• rapid growth rates

Question 3

What is small body size associated with?

Answer 3

Small body size is associated with limited gastric capacity, large surface area to volume ratio and high resting metabolic rate (RMR). These three characteristics have important implications for infant feeding.

Question 4

What does a large surface area to volume ratio mean and what are the implications?

Answer 4

An infant’s surface area to volume ratio is approximately twice that of an adult. This means heat and water loss is relatively greater in infants. As a result, infants have higher needs for energy and water per unit of body weight than adults.

Question 5

What are the three immature physiological functions that aren’t fully developed at birth?

Answer 5

Kidney function, swallowing reflex and gastrointestinal function is not fully developed at birth and have implications for infant feeding.

Question 6

Explain the mechanism and implications of immature kidney function

Answer 6

A critical aspect of physiological immaturity is an infant’s limited ability to concentrate urine. Older infants can concentrate urine to a level of 1000mOsmol/L, but younger infants may only be able to achieve a concentration of 600mOsmol/L. This means that they require more water to excrete a given quantity of waste.

Question 7

Explain the mechanism and implications of the immature swallowing reflex

Answer 7

At birth, there are three reflexes: rooting, suckling and extrusion. These reflexes enable infants to coordinate suckling, breathing and swallowing. Stroking an infant’s cheeks and lips stimulates the rooting reflex whereby infants will turn toward the stimulus to eventually come in contact with the nipple. Projection of the tongue following contact with the nipple and a rhythmic suckling action ensure maximal and efficient intake of breast milk or infant formula.

Question 8

What happens in the first 24 hours after birth?

Answer 8

Rapid changes in body composition occur soon after birth. During the initial 24-hour period, a newborn loses weight. Loss of water during the first days of life is an adaptation to the extrauterine environment in which the newborn’s skin is still maturing and there is a contraction of the extracellular water compartment soon after birth.

Question 9

What happens to body water up to one year of age?

Answer 9

Total body water as a percentage of body weight decreases from approximately 70% at birth to 60% at one year of age. This is predominantly due to a reduction in extracellular water. Intracellular water increases, which is associated with an increase in lean body mass.

Question 10

What are growth charts used for?

Answer 10

Growth charts are used to monitor growth from birth until the age of twenty years. Weight and length measurements are plotted on age and gender-specific growth charts and compared with the percentiles on the chart. A child who is on approximately the same percentile for height and weight and who is growing at a rate parallel to the next percentile line is very unlikely to have serious nutrition or chronic health problem.
For example, a boy aged 6 months weighs 8 kg and is at the 50th percentile. He is heavier than half the reference population and lighter than half the reference population.

Question 11

When might a growth chart indicate a health concern?

Answer 11

If a child’s growth percentile is changing a reason should be sought. For example, when it is near or crossing the upper or lower extremes, the 3rd and 97th percentiles. A trend towards weight loss over a month or more should prompt efforts to establish a nutritional cause or the existence of an underlying problem. However, it is important to remember that growth charts are tools, not a diagnostic instrument and further clinical evaluation is required to determine if there is a medical concern.

Question 12

Using the WHO Growth charts, what is the length of a boy aged 6 months on the 50th percentile?

Answer 12

68cm

Question 13

What are the three factors that infant energy needs are dependent on?

Answer 13

BMR, activity levels, and growth.

Question 14

Explain how energy requirements differ in the first year

Answer 14

• 3-6 months: Energy requirements fall between three and six months. This fall in energy requirements occurs because the very high growth rate observed during the first three months declines, but is not yet balanced by increased physical activity.
• 9 months: This fall in energy requirements is maintained until nine months.
• 12 months: As the growth rate slows, energy requirements decrease, and then increase again as activity levels rise towards the end of the first year. Even so, energy requirements per kilogram of body weight throughout infancy are three to four times greater than during adulthood.

Question 15

During the first year of life at what age are energy requirements the lowest?

Answer 15

6-9 months

Question 16

Which two factors contribute to the high energy requirements of infants?

Answer 16

• the large surface area to volume ratio.

- the deposition of body tissue

Question 17

What is the role and AI of protein in infants?

Answer 17

Infants require protein for the synthesis of new body tissue during growth, as well as the synthesis of enzymes and hormones. The 2006 adequate intake (AI) for protein for infants at 0–6 months is 1.43 g/kg/day.

Question 18

What is the role and AI of carbohydrates in infants?

Answer 18

Carbohydrate provides energy, spares protein as an energy source and prevents ketosis. The two main types of carbohydrates are:
- Lactose: The main carbohydrate in breast milk and cow’s milk is lactose. Breast milk contains 6–7% lactose (compared to 4.5–5% in cow’s milk) and breastfed infants obtain 35% of their energy from lactose. Lactose appears to facilitate the absorption of calcium and magnesium as well as preserving an acid medium in the lower intestine. The acid medium facilitates the growth of a Lactobacillus Bifidus flora and decreases the growth of Escherichia coli and other bacteria responsible for some forms of diarrhoea.
Oligosaccharides: Breast milk also contains around 1% of oligosaccharides and other nitrogen-containing carbohydrates. One of these, the L-Bifidus factor, is present in much greater concentrations in humans than in cows’ milk.

Question 19

What is the role and AI of fat in infants?

Answer 19

The dominant supply of energy during the foetal stage is glucose, whereas after birth this switches to fat, specifically triglycerides (12). In newborn preterm infants, 20–30% of dietary fat may be malabsorbed and excreted in the stools. Fat from breast milk or infant formula is the principal energy source for the newborn, supplying about 50% of total energy intake. It is an important component of an infant’s diet because it provides:

• a concentrated source of energy at a time when the growth rate is high and there is only a limited capacity for food intake.
• essential fatty acids including linoleic acid and α-linolenic acid.
• a vehicle for the fat-soluble vitamins A, D, E and K.

Question 20

What is the major source of energy in the infants diet? Rank the nutrients from the greatest to the least contribution to energy.

Answer 20

1 - fat
2 - carbs
3 - protein

Question 21

Explain what is meant by renal solute load and how it may be estimated

Answer 21

The renal solute load is measured in milliosmoles (mOsmol) per day. The renal solute load consists of the nitrogenous end products of protein metabolism, and electrolytes: sodium, potassium, phosphorus and chloride. A rough estimate of the renal load can be made using a rule of thumb which assumes that each gram of protein intake leads to the excretion of 4 mOsmol of urea and each millimole of electrolyte (Na, K and Cl) to the excretion of 1 mOsmol of renal solute.

Most adults are able to concentrate urine to 1,300 mOsmol/L. A younger infant may only be able to concentrate their urine to 600 mOsmol/L, an older infant to 1000 mOsmol/L.

Question 22

Under what circumstances, other than high environmental temperatures, might a healthy breastfed baby become dehydrated?

Answer 22

Dehydration occurs if the infant has diarrhea, a reduced volume of fluid consumption or if they are fed formula/cow’s milk with a high renal solute load.

Question 23

Why is it customary to express the energy and protein requirements of infants per kilogram of body weight, rather than per day, as for other age groups?

Answer 23

There are large variations in the rate of growth among infants. Weight at birth, prematurity and energy requirements vary widely and are not the same for all infants at the same age. For example, one infant might be 4.0kg at birth and another 2.5kg at birth, and so the energy and protein requirements for these infants would be very different.

Question 24

Recommended energy intakes for infants expressed per kilogram of body weight are lower at 6–9 months of age than at 1–2 months or at 11–12 months of age. What is believed to be the basis for this pattern of energy needs?

Answer 24

Energy requirements are lower at 6-9 months as this is a period when the rate of growth slows and infants are not very active. The very high growth rate characteristic of the first three months of life has declined but is not yet balanced by an increase in physical activity.

Question 25

On average, how much energy per kilogram of bodyweight does 850 mL of human milk provide for an infant on the 50 percentile for weight at age six months?

Answer 25

Energy for 8kg infant, 850 ml milk, breast milk 280kJ per 100ml = 850/100*280 = 2380kJ Then divide by 8.0kg =297.5kJ/kg

Question 26

Explain why breast milk, which contains only 6–7% of energy from protein, is adequate for the rapid rate of growth that occurs in early infancy.

Answer 26

Protein is not primarily used as a source of energy. Protein provides essential amino acids for the growth and synthesis of enzymes, hormones and other physiological compounds. Energy needs are not met by protein, but by fat and then carbohydrate.

Question 27

What are the major advantages of a diet providing a higher proportion of energy from fat (50–54%) than from carbohydrate (40–43%) in infancy?

Answer 27

A higher fat diet is more energy-dense and provides more energy in a smaller volume which is required when the growth rate is high. Infants have a small gastric capacity and can only tolerate a low renal solute load. A high-fat diet provides energy without additional stress on the kidney to excrete waste products and is also a vehicle for fat-soluble vitamins.

Question 28

What is the rationale for higher mineral concentrations in infant formula compared with breast milk?

Answer 28

The absorption of iron, calcium and perhaps zinc is reduced in formula-fed infants.

Question 29

Under what circumstances are mineral imbalances most likely to arise in Australian infants?

Answer 29

Nutrient imbalances arise when cow’s milk is consumed before 12 months and this can result in iron deficiency anaemia if iron fortified foods and good sources of iron are not included in the diet. Also, premature babies and low birth weight infants given vegetarian diets are at greater risk of iron deficiency anaemia. Infants are also at greater risk of vitamin D deficiency if the mother’s vitamin D status is low – low vitamin D in breast milk can result in deficiency in infancy leading to rickets and disorders of calcium metabolism.

Question 30

A parent is making a bottle of S26 infant formula, usually made with 240 mL water and four-level scoops of powder. Unfortunately, this parent is confused and is only adding in three instead of four scoops. What are the consequences of this error if this practice continues for a few months?

Answer 30

The child would be receiving inadequate carbohydrate, fat and protein and therefore energy and would not be growing at the correct rate (in addition to insufficient levels of most vitamins and minerals risking inadequacy). Growth is likely to be reduced as there is insufficient energy for growth and amino acids.

Question 31

A father is concerned that his 8-month-old daughter is not consuming sufficient protein. The father has decided to stop giving fruit and vegetables because he has heard these foods are low in protein. Instead, he is giving more dairy foods, meats and chicken. In addition, he is adding a protein powder to the infant formula. Comment on the dietary practices of this father.

Answer 31

The father is providing too much protein. At this point, growth has slowed. Increasing protein will increase the renal solute load and the exclusion of fruit and vegetables means a reduction in water-soluble vitamins, antioxidants and dietary fibre, the latter contributing to constipation.

Question 32

The local childcare centre has made a change to the feeding practices in the babies’ room (children aged six weeks to one year) and is asking for your expert opinion. The childcare centre has replaced infant rice cereal with Weet-Bix for infants who are aged six months. In addition, they are also introducing a bottle of orange juice with the Weet-Bix. Discuss the implications of this change. (Hint: it would be useful to look at the nutrition composition of both Weet-Bix and rice cereal. You can obtain this information from the supermarket.)

Answer 32

Weetbix is wholegrain and therefore, higher in dietary fibre; however, it is lower in iron. Anaemia can be a risk for children moving to a mixed diet and ceasing formula at 6 months.

The orange juice could increase the absorption of iron, but fruit juice is not recommended for infants as excessive consumption can lead to diarrhoea, gastrointestinal disturbances, dental caries, a preference for sweetened foods and fluids and replaces the nutrient-dense breast milk or infant formula.

Question 33

Rickets is known to occur in exclusively breastfed infants of Muslim mothers. It is typical for Muslim women to cover their entire body with clothing (except for their face) and to spend long periods indoors. Explain how rickets would occur in this situation.

Answer 33

Vitamin D status is determined by exposure to sunlight. There is insufficient vitamin D in foods in Australia to maintain plasma levels of vitamin D without sunlight exposure. Women who are dark-skinned and are covered from the sun are likely to be vitamin D deficient, and their infants also are born with low or no stores of vitamin D. The vitamin D content of breast milk reflects the vitamin D status of the mother, so a breastfed infant of a vitamin D deficient mother is likely to have a vitamin D deficiency and develop rickets.