Diet and the Lifecycle

CHAPTER 6 Diet and the Lifecycle






6.2 NUTRITIONAL ASSESSMENT IN CHILDHOOD


Body weight for age (WFA) is frequently used as an indicator of nutritional status but weight is heavily influenced by height. Childhood nutritional assessment (see also chapter 12) commonly uses either weight-for-height (WFH) independent of age, or WFA in relation to height-for-age (HFA). Reference standards for growth and development do not distinguish the abnormal from the extremes of normal. Scores of <−2 or >+2 SD, or <3rd and >97th centiles, are often used as cut-off points for ‘normality’. Velocity of growth may be more informative than size attained.





6.3 DEVELOPMENT AND MATURATION



Physical maturation


Growth from the fetus through infancy and childhood is clearly one aspect of physical maturation before the onset of puberty when rapid physical maturation occurs. The age at onset of puberty and the pubertal growth spurt vary widely between individuals. Secular trends towards increased height and weight and earlier age at puberty, attributed to positive changes in health and nutrition, have slowed or ceased in recent years in much of Europe and North America, but continue elsewhere.


The typical age for onset of the secondary sexual development characteristic of puberty is considered to be between 8 and 13 years in girls and 9 and 13.5 years in boys with similar mean age (11.5 years) in both sexes. In girls the growth spurt always occurs early in the progression of puberty with most rapid growth in height on average 0.7 years after the first signs of puberty and before menarche. Growth acceleration in boys occurs later in the pubertal process, with most rapid growth occurring on average 1.5 years after the first signs of puberty, and continues longer than in girls. Peak bone mass is achieved two years after cessation of growth (mean: girls 16 years; boys 18 years). Pubertal changes in body size and composition lead to greater differences in nutrient requirements between males and females than were present in earlier childhood. In adolescent girls the nutritional needs of pregnancy and lactation may have to be added to those of growth and menstruation. In adolescent boys increased lean body mass leads to greater nutritional demands per kg body weight (see Appendix 2).








6.4 NUTRITION IN INFANCY



Breast milk


There is now almost universal consensus that breast milk is the best food for normal infants with healthy mothers, because of its composition, digestibility, and anti-infective properties. Despite this consensus, most one-month-old infants in UK have received some infant formula and by 10 weeks 64% of infants are wholly formula fed. It is proving difficult to improve ‘breast feeding statistics’ in UK despite widespread education and publicity promoting breast feeding.


The composition of human milk is variable. The first milk, colostrum, is low in volume and high in proteins, especially immunoglobulin A, as well as vitamin A and zinc. As the volumes of milk secreted increase, milk composition modifies to ‘transitional’ and then ‘mature’ milk. Table 6.1 outlines the biochemical composition of colostrum, human milk, modern infant formula and cow’s milk. Volumes of milk produced and precise composition of breast milk vary between women, over time and by time of day. Human milk contains cells (macrophages, lymphocytes, neutrophils) and humoral components, eg sIgA, which protect infants against infection in the first months of life. Lactobacillus and Bifidobacterium spp promote lactic and acetic acid production from lactose, which discourages growth in the large bowel of potential pathogens such as E. coli and Shigella spp.



Lactose, the main carbohydrate in milk, accounts for approximately 40% of total milk energy and facilitates calcium absorption. Human milk protein is 30–40% casein and 60–70% whey. Whey proteins include lactalbumin, sIgA, lactoferrin and lysozymes, whereas casein is a mixture of proteins bound with calcium. Human milk casein forms smaller micelles with looser structure than the casein of cow’s milk, which facilitates digestion. Nutrient binding proteins in milk such as lactoferrin (which binds iron) facilitate absorption of some specific nutrients. The quantities of fat in human and cow’s milk are similar, but human milk fat is higher in unsaturated fat, particularly the essential fatty acids linoleic and α-linolenic acids, and also contains the long chain polyunsaturated fatty acids arachidonic, eicosapentaenoic and docosahexaenoic acids (22:6ω3), which are important for neurological development (see chapter 4).


The fats in human milk are more readily digested and absorbed than those of cow’s milk. Most infant formulas now contain mainly vegetable oils with rather different proportions of fatty acids than those found in human milk fat, which partly depends on maternal dietary fatty acid content. Human milk has a high level of cholesterol and of carnitine, which is involved in mitochondrial oxidation of fatty acids. Premature infants and those undergoing very rapid (catch-up) growth may be unable to synthesize carnitine at a sufficiently rapid rate to meet demand.






6.5 THE TRANSITION TO MIXED FEEDING: WEANING OR COMPLEMENTARY FEEDING



Definitions


Weaning, also known as complementary feeding, has been defined as ‘The process of expanding the diet to include foods and drinks other than breast milk or infant formula’. Since the term ‘weaning’ is also used to indicate complete cessation of breastfeeding, WHO recommends that the terms ‘weaning’ and ‘weaning foods’ are avoided. The term complementary feeding is used here to embrace the use of all foods and liquids other than breast milk or infant formula.


Maternal milk output averages 650 ml/day at one month of lactation, 750 ml/day at 3–4 months’ lactation and peaks at about 900–1000 ml/day at 4–5 months’ lactation. Average infants would need 850 ml and 1450 ml of breast milk to meet energy requirements at 6 and 12 months respectively on exclusive breast feeding. From six months, and probably before this for some infants, additional sources of energy and nutrition are needed to complement breast milk. The World Health Organization and the UK Department of Health have formally adopted the policy:



However, a survey in 2000 found that 90% of infants are introduced to some non-milk, non-formula, food before 4 months, despite education about the age of introduction of complementary foods.



Maternal choice in complementary feeding


Depending on the choice of food, complementary feeding can provide necessary extra energy and micronutrients. It encourages development of feeding techniques and ability to eat with the family, but is less likely to be sterile and early introduction can lead to allergic reactions to foods.


Complementary foods may be home prepared or commercially produced. Initially one small feed is introduced per day but feed frequency can increase quite quickly. Whilst breast milk (or formula) remains the main source of energy early in complementary feeding, cereal based complementary foods, with energy density enhanced by additional fat source, should be introduced early. Rice preparations are usually recommended since rice is gluten free. With wheat based foods there is slight risk of malabsorption from either temporary gluten intolerance following gastrointestinal infection, or permanent gluten intolerance in coeliac syndrome. Fats increase the energy density of foods, thus facilitating energy sufficiency and optimum infant growth with the relatively small volumes of food tolerated by infants’ small gastric capacities. Fats are also sources of fat-soluble vitamins, essential fatty acids and exogenous cholesterol and enhance taste and food texture and therefore palatability. Provided breast milk, formula, or (later) cow’s milk intakes are around 500 ml/day, protein intakes are likely to be adequate even if complementary feeds are low in protein and amino acid variety (eg in diets with a single plant staple).



Home-prepared versus commercial complementary foods


About 40% of home prepared complementary foods have an energy content lower than breast milk and are lower in fat, iron and vitamin D and higher in sodium than commercially prepared infant foods. UK legislation specifies a range of nutritional contents for commercially produced infant foods. Thus infants receiving commercial complementary foods may have more balanced nutrient intakes than those fed home prepared foods. If only commercial fruit, vegetable and pudding products are offered as complementary foods, energy needs are unlikely to be met as the foods displace breast milk and formula in the diet but are usually less energy dense.


Early foods offered are semisolid. Infants quickly learn to cope with solid and lumpy foods and ultimately foods which require chewing prior to swallowing. This progression is important. Prolonged bottle feeding (beyond one year) can lead to failure to thrive due to the ‘comfort’ aspect of sucking and the low energy density of fluids proffered. Infants should be moved from fluids fed by bottle to predominantly fluids fed by cup over the second six months of life. Current UK recommendations are that cow’s milk should not be given as a drink to infants under one year, but when it forms part of family recipes, small amounts may be safe before this age.




6.6 NUTRITION IN CHILDHOOD AND ADOLESCENCE


Digestion and absorption in preschool children enable them to consume the same foods as adults but nutrient needs and feeding skills are different. Children’s small stomachs limit the amounts of food taken at any one meal. They should therefore be fed three meals a day and perhaps two between-meal snacks, with one snack or meal close to bedtime. Recommendations for adults to consume <35% dietary energy from fat do not apply to young children. The transition from >50% dietary energy derived from fat provided by exclusive breast feeding to <35% energy derived from fat should spread over the first five years of life. Similarly adult recommendations for fibre intake should not apply in early childhood since high fibre content lowers food energy density and phytates reduce absorption of micronutrients. Diets with <30% energy derived from fat are quite common amongst preschool children who consume large quantities of ‘juice’ and sweets instead of meals of varied content. They are likely to lead to failure to thrive if prolonged. Persuading children to eat family meals is not always easy. Children are often reluctant to eat green leafy vegetables, partly due to inexperience with chewing.



Nutritional problems in children and adolescents



Jun 13, 2016 | Posted by in ENDOCRINOLOGY | Comments Off on Diet and the Lifecycle
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