See Bibliography for references.
See Bibliography for references.
(LRNI), the level below which intakes are likely to be inadequate for the large majority of the specified group. It is taken as the mean -2 SD.
A fourth type of value is published when there is insufficient information to determine the other types. In the United Kingdom, safe intakes are specified when there is not enough information to estimate RNI, EAR, or LRNI. This is the amount that is sufficient for almost everyone in a specified group but not so large as to cause undesirable effects. In the United States, when insufficient evidence exists to determine EAR, an adequate intake (AI) is specified. This is intended to cover the needs of most individuals in a specified group but the percentage cannot be stated with certainty. Therefore, these are at a level comparable to RNI and RDA but have even more uncertainty about them. In the United States, AI rather than EAR or RDA has been proposed for all nutrients for infants up to 1 year old and for calcium and vitamin D for all life stages.
Finally, the maximum level that is unlikely to pose risks to health in almost all individuals in the specified group is called the tolerable upper intake level (UL) in the United States. This does not mean that intakes above RNI or RDAhave known nutritional benefits. Also, for many nutrients, there is insufficient data on the levels at which adverse effects occur.
According to FAO/WHO/UNU1:
The energy requirement of an individual is the level of energy intake from food that 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 that will allow for the maintenance of economically necessary and socially desirable physical activity. In children and pregnant and lactating women the energy requirement includes the energy needs associated with the deposition of tissues or the secretion of milk at rates consistent with good health.
Not every nutritionist feels comfortable with this definition, because of the problems in establishing what is a state of long-term good health and the possible subjectivity of socially desirable physical activity. However, a more immediate problem is the need to know the energy expenditure. This can be approached at a variety of levels. An estimate can be made knowing the age, sex and weight of the child and assuming a type of lifestyle—inactive, moderately active, and so forth. At the other end of the range of approaches is the measurement using stable isotopic doubly labeled water. This has the disadvantage of being expensive and lacking information on the components of the energy expenditure. Somewhere in between is the factorial approach of recording the time and duration of activity and applying energy costs either measured or taken from the literature to these to calculate energy expenditure.4 It can be seen that there are considerable differences in the certainty of estimates of energy expenditure from these different approaches and, hence, in the estimates of energy requirements.
The protein requirement of an individual is defined as the lowest level of dietary protein intake that will balance losses of nitrogen in persons maintaining energy balance at modest levels of physical activity. In children and pregnant or lactating women, the protein requirement is taken to include the needs associated with the deposition of tissues or the secretion of milk at rates consistent with good health.1
The adequacy of a protein intake is influenced by the adequacy of the energy intake. When energy intake is inadequate, there may be a net negative nitrogen balance that reduces the adequacy of the protein intake. Thus, information on energy and protein intake need to be considered together. One way of doing this is the protein-energy ratio (PE ratio: protein energy/total energy). When the diet exceeds the safe PE ratio, then any protein nutrition problems will result from inadequate amounts of food rather than low protein content. Most regular diets have PE ratios between 10 and 15%. Human breast milk has a PE ratio of about 7% and is adequate for the rapid growth in the first months of life. In the absence of other detailed information, this figure can be applied to other stages of growth. An allowance has to be made for the efficiency of utilization of the protein, which in most cases is less than that of breast milk.
These usually have been assessed by balance techniques. An alternative approach common in North America is to identify the dietary intake associated with the highest levels in the body. These different approaches explain much of the differences in the United Kingdom's RNI and the United States' AI described earlier.
Dietary goals and guidelines differ from dietary recommended intakes and dietary reference values. Dietary guidelines provide advice on food selection that will help meet the RDAor RNI and help reduce the risk of disease, particularly chronic disease. They are thus meant to ensure adequate intake to prevent deficiency states and prevent the inappropriate macronutrient intakes associated with many of the chronic degenerative diseases of affluent societies. The goals set what is to be achieved to reduce the incidence of these diseases in terms that are understood by the professionals; that is, reduce intake of nutrient x to y g per day. The guidelines indicate to the public how the goals are to be achieved. They refer to foods and diets as opposed to nutrients. As most of us base our diet on foods rather than nutrients, they are much more relevant to the population.
The most well-known dietary guideline is to eat a variety of foods. This is usually portrayed as a food block, plate, or pyramid of 4-5 food groups that recommends the kinds and amounts of foods to be eaten each day. The United States' food guide pyramid indicates fats, oils, and sweets are to be used sparingly, but there can be 6-11 servings of bread, cereal, rice, and pasta. The United Kingdom's national food guide uses a picture of a plate with less prescription on servings but essentially the same advice.
Dietary guidelines are regarded as applicable to the whole population. Australia and New Zealand produced guidelines specifically for children of different ages, which allow for fuller consideration of types of infant feeding and the nutritional problems of adolescents. The United States has a food guide pyramid for young children, meant to be accessible to 2-6 year olds.5
Values of recommended intakes and dietary goals and guidelines have another important use in addition to assessing or planning diets. This is in the information given on and claims made for food products, particularly on labels. Food manufacturers are interested in dietary recommended values and legislation about food composition and claims. They are important members of the committees that draw up guidelines, often with interests separate to those of nutritionists and clinicians. This may not be counterproductive, as differing views may lead to better evidence on requirements and recommendations in the long term.
The assessment of the nutritional status of an individual or group involves the collection of information: on diet, biochemical indices, anthropometry, clinical signs, and morbidity and mortality statistics. The value and place of this disparate group of measurements can best be understood by considering the process of becoming malnourished. Figure 7-1 shows the process of moving from a state of good nutrition to malnutrition and eventually death and shows the place of each type of measurement. The aim should be to correctly describe an individual or group as well nourished, at risk, to be monitored further, or in need of remedial action.
The directionality of the process may need to be established by serial measurements, as for example, poor scores on biochemical, anthropometric, and clinical data may persist for sometime after the diet has improved. Good dietary assessment is difficult, time consuming, and expensive; and its interpretation is rarely clear-cut, given the nature of knowledge of nutritional requirements, and this is often omitted. However, it can be crucial in establishing the true pathogenesis, as many of the other signs are not specific to nutrition but can also arise from other environmental causes such as disease. A wide-ranging ecological assessment may be the only way to ensure that the true causes of low nutritional status are identified and the appropriate remedial action is taken.
The emphasis in assessment is to obtain early warning signs of malnutrition, and the biochemical indices play an important role here. Simple dietary iron deficiency will result in iron-deficiency anemia (low levels of hemoglobin, with microcytic and hypochromic erythrocytes) if left untreated. Before hemoglobin levels fall, body stores diminish. This is described as iron deficiency without anemia. In
Well ■*->■ At risk <-*-*-> Malnourished nourished
Physiological and metabolic alterations
Clinical signs Morbidity stats
Dietary signs figure 7-1 The process of becoming malnourished and the place of the elements of nutritional status assessment at different stages of the process. (Derived from Sabry ZI. Assessing the nutritional status of populations: Technical and political considerations. Food Nutrit. 1977;3(4): 2-6.)
examining data on nutritional deficiencies, it is important to distinguish between those based on "biochemical" deficiencies and those based on "clinical" signs, in terms of establishing the importance or priority of the problem. Some would have it that assessment of nutritional status should be based more firmly on functionality rather than low levels of body chemicals or size. There is much truth in this, but the cutoff points to identify good and poor nutritional status from these indices are based on outcomes and impairments wherever possible.
Anthropometry plays a major role in nutritional status assessment particularly in field and clinic studies of children. Growth faltering is regarded as an early sign and symptom of poor nutrition, and nutritionists rely heavily on anthropometry for indices of nutritional status. Not all causes of impaired growth are nutritional in origin. Most commonly, growth can be impaired by disease and infection and an associated anorexia or poor appetite. The significance of this is that the first priority may be to treat concurrent infections and eradicate their causes rather than attempt refeeding or development projects in agriculture or subsistence food production. The provision of clean, protected water supplies and sanitation may also be an early priority.
In nutritional status assessment, the "growth" of a population is often described by cross-sectional measurements. There is a risk of circularity in a discussion of nutrition and growth when growth is used as a proxy for nutritional status. The interpretation of a particular size, whether a small child is normally small or growth retarded, is a difficulty, but one outside the scope of this chapter. Height, or length, is a key variable for auxologists, but nutritionists are particularly interested in growth of muscle mass, adipose tissue mass and its location, and bone mass because of the greater direct functional implications and the consequences for long-term good health.
nutrition and growth
The importance of nutrition for growth is well attested by clinical observations of growth reduction in conditions of reduced food intake, such as anorexia nervosa, and in intestinal malabsorption, such as is associated with untreated cystic fibrosis. At the population level, growth faltering has been observed and well documented to be associated with food shortages in conditions of civil unrest and war. However, nutritional challenges to growth rarely occupy precisely circumscribed epochs and even more rarely do they operate in a vacuum. The secular trends in growth, menarche, and skeletal maturation observed in many countries over the last 100 years are a record of the effects of previous living conditions on growth. Most commentators ascribe a key role to improvements in nutrition in these secular changes (see Chapter 9). Nutrition is one of a number of environmental influences on growth. The others include infection, poverty, poor housing, and schooling; and it can be difficult to identify and evaluate the precise contribution of nutrition to growth or growth failure. The type, duration, and intensity of the nutritional challenge influence the nature of the response in growth, as does the ecological setting. There is thus no quantitative lawlike relationship between nutrition and growth, and descriptions of the relationship tend to be either rather general or biosocial case histories.
Maternal and fetal nutrition and nutrition in infancy, childhood, and adolescence are topics well covered in many textbooks on nutrition. Most are specific to a par ticular region (e.g., North America or Europe), and few are balanced according to developed country issues. The aims of this chapter do not include teaching basic nutrition, and it is not covered in any detail. Some representative texts are listed in the Annotated Bibliography.
The infant grows faster in the first year of life than at any subsequent period of life, and breast-feeding is recognized as the appropriate method of feeding the newborn and infant in the first months. The advantages expand beyond the provision of a feed nutritionally suited to the human infant that is hygienic and at the correct temperature and with a built-in supply regulator. They extend to better immune competence and more protection against gastroenteritis, ear, and chest infections, eczema, and childhood diabetes. For the mother, there is a speedier reduction in size of the uterus and a lower risk of premenopausal breast cancer, ovarian cancer, and hip fracture. For a variety of reasons, some mothers choose not to breastfeed or may be unable to breast-feed. These women should have as much support as breast-feeders and should not be made to feel guilty or inadequate.
A basic assumption is that breast milk composition has evolved to meet the nutrient needs of the infant. If the amount produced is sufficient, that is, if energy needs are met, so are nutrient needs. Breast milk intake of 850 ml/day would meet the needs of infants growing along the 50th centile until 4 months old.6 It would meet the needs of an infant in a developing country growing along the 25th percentile for 6 months. Weaning should begin at these ages.
Breast-fed babies have in the past been found to grow more slowly in infancy than formula-fed infants in some but not all studies. This meant that breast-fed children often appeared to be growing less satisfactorily than reference growth data as the older growth reference data came from groups of exclusively or mostly formula-fed infants. There is some evidence that this difference has lessened as formula feeds have been "humanized"; that is, modified toward the composition of breast milk. Fears that formula-feeding may promote the development of widespread overfeeding and obesity have not been founded. The other major concern of infant nutrition in developed countries, the premature introduction of solid foods, is being addressed by information and education programs.
Table 7-1 shows the United Kingdom's RNI and the United States' AI for selected nutrients for children 1-10 years old. Some of the biggest differences are for calcium. There is currently no international consensus on recommendations for calcium intake. The United States currently recommends 800 mg/day for children, based on the maximal retention of calcium in bone. In the United Kingdom, lower figures of 350-550 mg/day have been recommended, but based on a factorial approach with allowances for gain, loss, and absorption.
Nutritional needs in adolescence may be, in absolute terms, greater than at any other time of life. The high rates of proportionate growth may only equal or be less than those of the first few months of life, but they persist for much longer. It is a time when individuals make more of their own choices in food, in some cases using them as part of a relationship struggle with parents and caregivers, but without necessarily too much nutritional knowledge. Independence, or the pursuit of it, may lead to behaviors, such as anorexia, bulimia nervosa, and substance abuse, that threaten nutritional integrity and hence growth. However, the growth of teenagers can be remarkably resilient to nutritional challenges, as illustrated later when considering the pubertal growth spurt in poorly nourished Indian adolescents.
Good nutrition is of fundamental importance to growth. When food becomes limited, one of the earliest responses of the body is to retard growth; indeed, growth assessment by anthropometry is one of the most commonly used indices of nutritional status. Similarly, deficiency of a single nutrient, such as zinc, may cause growth failure. It is easy to move from this to the idea that growth is a costly process that requires most of the energy and nutrient intake. This may be true for some mammals but not for humans, with the exception of the first few months of life. Figure 7-2 shows the energy cost of growth from infancy to adulthood and the usual energy intake over this period. It can be seen that the requirements for growth make up less than 10% of the total energy intake for most of the growth period. However, as growth is in the front line of responses to nutritional challenges, problems are common.
Malnutrition means bad nutrition. The term applies equally to overnutrition as to undernutrition, but it tends to be used more for the latter than the former. It has been estimated that the proportion of the world's population exhibiting overnu-trition now matches that showing undernutrition. However, the sequelae of over-nutrition may take their toll in adulthood; for example, as cardiovascular disease or non-insulin-dependent diabetes mellitus. In contrast, the sequelae of hunger and undernutrition—that is, increased susceptibility to infectious disease, physical and mental impairment, and possibly death—affect the young most; and undernutri-tion is given more prominence here.
Growth retardation in developing countries is said to be most common and most marked between 6 and 12 months of age. This timing is the intersection of infant and childhood phases of growth, a time when the system is unusually sensitive to stress or perturbation. It is also a time of high growth velocities and nutritional needs and of the troublesome period of weaning. Growth retardation at this time is most severe in infants of low birth weight. This, plus the concerns of long-term implications for health in adult life and intergenerational effects on growth, emphasize the importance of fetal and maternal nutrition. However, it must be remembered that poor fetal growth is a marker for poor socioeconomic factors in general, which lead to a more stressful and less successful life. Control for such factors is notoriously difficult, and its absence or failure seriously weaken inclusive hypotheses of intrauterine nutrition and adult disease.
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