(i) Food allergies. Adverse food reactions are divided into two general categories: food intolerance and food hypersensitivity. An allergic reaction to a food involves the immunologic system. The incidence of food allergies has been estimated at 8% in the first year of life, and decreases as children get older; however, most further qualify it to be in the 1% to 2% range (Bock, 1987). The risk of developing food allergies is largely related to genetic predisposition and the age at which the food is introduced, with the chance of sensitization greatest in the first year of life. Young infants are especially prone because their immature intestinal system is more permeable to absorption of food allergens and lacks local immune defences (Burks and Sampson, 1993). Most allergens are proteins of large molecular size, therefore food allergy commonly presents in infancy with the first introduction of milk, egg or peanut (Burks and Sampson, 1993). These three foods, as well as soy, nuts and wheat, are responsible for about 95% of food allergies in infants (Bock and Atkins, 1990). It is rare for an infant to have allergies to more than two or three foods (Bock and Atkins, 1990). In an exclusively breastfed infant, the source of these allergens can be the mother's diet. The proteins pass into her breast milk and thus are ingested by the baby (Jakobsson 1991).
Diagnosis of food hypersensitivity requires a careful history to exclude other causes of adverse food reactions, selective skin prick testing or radioallergosorbent test (RAST) (when IgE mediated disorder is suspected), appropriate removal of the food from the diet, and a subsequent challenge test (Bock and Sampson, 1994; Burks and Sampson, 1993).
Treatment of food hypersensitivity involves avoidance of foods proven to cause symptoms. Food-related allergies tend to disappear with age, therefore rechallenging with the offending food is recommended at regular intervals (Bock, 1986). Allergies to peanut, nuts, wheat, fish and seafood are the most severe and tend to be lifelong (Burks and Sampson, 1993). In the case of multiple food allergies or severe reactions to food, the assistance of a dietitian with expertise in food allergies may be beneficial.
The ability to prevent food hypersensitivity is being debated. Exclusive breastfeeding for at least 4 months has been shown to decrease the risk of allergy in infants at increased risk of food allergies. The use of protein hydrolysate formulas and the delayed introduction of solid foods have been studied for prophylaxis of food hypersensitivity. Many of the studies are conflicting. (For further discussion of this topic, see the sections on breastfeeding and the prevention of allergies, and protein hydrolysate formulas.) A single recent study showed that exclusive breastfeeding, or feeding a formula containing a partially hydrolyzed whey-hydrolysate, was associated with lower incidence of atopic disease and food allergy compared to feeding soy or conventional cow's milk formulas
Various pharmacological treatments have been tried but none has been proven to be of definite benefit. Simethicone, a defoaming agent, has been most extensively studied. It is said to accelerate the passage of intestinal gas by decreasing the surface tension of gas bubbles.
Controlled studies show varying results, although most did not show any benefit (Becker et al., 1988; Sethi and Sethi, 1988; Dugger and Inchaustegui, 1963; Danielsson and Hwang, 1985). Most recently, Metcalf et al. completed a randomized, placebo-controlled, multicentre trial which demonstrated that simethicone was no more effective than a placebo (Metcalf et al., 1994). Because colic is associated with gastrointestinal discomfort and certain herbal teas have been cited as having antispasmodic activity, herbal teas have been used to treat colic. Weizman and colleagues recently demonstrated in a prospective double-blind study that a herbal tea containing chamomille (Matricaria chamomile), vervain (Verbena officinalis), licorice (Glycyrrhiza glabra), fennel (Foeniculum vulgare) and balm mint (Melissa officinalis) appeared more effective than a placebo in improving infant colic (Weizman et al., 1993). This study was limited in that the measure of outcome was based on parents' subjective evaluation and the study duration was short. Further studies are needed before this intervention can be routinely recommended since the safety of some herbal teas if taken in large amounts has not been established.
(iii) Constipation. The definition of constipation in early childhood is elusive (Forsyth et al., 1985). Stool patterns vary normally from child to child. In infancy, true constipation is infrequent. There is wide variation in the "normal" number of bowel movements per day, ranging from a bowel movement days apart, to one after each feeding (Rappaport and Levine, 1986). Normal bowel function occurs even when an infant appears to be in extreme discomfort as evidenced by straining and reddening of the face. There is no evidence that inadequate fluid or carbohydrate intake is the cause of constipation in infants; nor is there evidence that treating constipation with fruit juices or corn syrup is efficacious. Educating parents about the wide variation in normal bowel function seems essential for avoiding the overtreatment of normal variants.
Hard and painful bowel movements signal a mild to moderate problem in bowel function, whereas abdominal distention requires further work-up and medical intervention. The use of prune juice (with its high sorbitol content) and/or increasing the fibre content of the diet may be helpful for infants older than 6 months. A varied intake of fibre-containing foods such as whole grain breads and cereals, fruits, vegetables and cooked legumes is suggested rather than the routine use of fibre supplements (Agostini et al., 1995). There are no data regarding the amount of fibre needed for normal laxation during the first 2 years of life. Recent recommendations on dietary fibre intake for children (age plus 5 g/day) apply to children older than 2 years (Williams et al., 1995). These recommendations to a large extent reflect current dietary intake of fibre by children in North America. They are not based on evidence of disease prevention. Concerns related to increased consumption of fibre in infants and toddlers include a possible decrease in caloric intake resulting in inadequate growth and development, decreased bioavailability of minerals, and an increase in intestinal gas and abdominal discomfort. Studies in older children and adults suggest that these concerns may be unfounded (Dwyer, 1995).
This sign of excess fluoride intake has led to modifications in fluoride recommendations such that fluoride supplements are no longer recommended from birth, and doses have been decreased during the first 6 years of life. The difficulty lies in knowing how far to lower fluoride supplementation without jeopardizing the benefits of caries prevention. The diversity in drinking water supply and dental hygiene practices in Canada, and the lack of comprehensive epidemiological data, have made it difficult to reach agreement on the best way to provide the right amount of fluoride to all Canadian children.
Recently the Canadian Paediatric Society (CPS) and the Canadian Dental Association (CDA) participated in a consensus conference organized to unify an approach to fluoride supplementation for infants and children living in Canada. The proposed new recommendations (CDA, 1998) would replace the existing CPS (CPS, 1995) and CDA (Clark, 1993) recommendations; they include a decision-algorithm for use by health care providers as well as a new recommended dosage schedule of daily fluoride supplementation (see Table 1). The goal is for all organizations to work together to implement this uniform fluoride supplement schedule in Canada.
As more information becomes available from monitoring trends in dental fluorosis, the optimal timing and dose of fluoride supplements needed to prevent dental caries, and avoid dental fluorosis, may require further revision. It should be noted that "ready-to-serve" infant formulas in Canada are not fortified with fluoride.
Table 1. Dosage Schedule for Dietary Fluoride Supplements (mg/d)
If fluoride concentration of principal drinking water source is:
Birth - 6 mo none none
The timing of the diet-IDDM interaction in humans remains to be established. Although hydrolyzed casein-based diets are diabetes-retardant in animal models of IDDM, the use of hydrolyzed casein-based infant formulas for prevention of diabetes in high-risk human infants is not recommended because prevention of diabetes may require avoiding diabetogenic foods long past the time of infancy and these formulas are unpalatable and expensive. Knowledge of the food diabetogens, and particularly the mechanisms by which they cause diabetes, is still incomplete, making it difficult to justify dietary intervention trials in children at this time. Until more definitive data are available on the timing, duration of exposure and the exact identity of all the foods that may promote diabetes, it is inappropriate to recommend changes to infant feeding practices.
(viii) Iron deficiency anemia. Iron deficiency is most common among infants between the ages of 6 and 24 months. The major risk factors for iron deficiency anemia in infants relate to socioeconomic status, the early discontinuation of breastfeeding and include the early consumption of cow's milk, and inadequate funds for appropriate foods (Canadian Paediatric Society, 1991; Gray-Donald et al., 1990). Other high-risk groups include low birth weight and premature infants (Friel et al., 1990; Shannon, 1990), and older infants who drink large amounts of milk or juice, and eat little solid food (Feightner, 1994). The importance of preventing rather than treating anemia has been emphasized by findings that iron deficiency anemia is a risk factor for what may be irreversible developmental delays in cognitive function (Lozoff et al.,
Healthy full-term infants are born with neonatal iron stores which can meet iron needs until 4 to 6 months of age (Calvo et al., 1992; Saarinen and Siimes, 1977). At this time, the absorption of highly bioavailable iron in human milk may no longer be adequate to meet the demands for erythropoiesis. Therefore, introduction of iron-fortified infant cereals is recommended as a good source of available dietary iron at 4 to 6 months of age (Fuchs et al., 1993; AAP, 1992b; CPS, 1991). For non-breastfed infants, switching from a non-fortified to iron-fortified formula around 4 to 6 months of age would meet the need for supplemental iron. However, parents may forget or ignore the need for a change in formula; therefore, as a preventative measure, it is recommended that for non-breastfed infants, an iron-fortified formula be used from birth (CPS, 1991). Although dietary iron is not used for hemoglobin synthesis in the first few months of life, its early use contributes to iron stores and helps to prevent later development of iron deficiency. In communities where the majority of formula used is iron-fortified, the prevalence of iron deficiency anemia is very low. The perception by parents and some health professionals that low-iron formulas are associated with fewer gastrointestinal symptoms has not been demonstrated in controlled clinical trials. No difference in gastrointestinal symptoms or stool characteristics (with the exception of colour) has been detected in infants fed low-iron and iron-fortified formulas (Nelson et al., 1988; Oski, 1980).
Infants weaned from breastfeeding before 9 months of age should receive iron-fortified formula. Non-fortified formula and cow's milk are unsuitable alternatives as they contain very little natural iron which is poorly absorbed. When milk is combined with other dietary sources of iron, such as iron-fortified infant cereals, pureed liver, meat, fish, legumes and egg yolk, it may be possible to avoid iron deficiency and anemia. However, there are limited data to support or refute this estimation. After 9 months of age, when a wider variety of foods is being ingested, the introduction of cow's milk is not associated with any risk of iron deficiency. Despite recommendations to the contrary, many Canadian infants receive cow's milk or evaporated milk in the second 6 months of life because of convenience and relatively low cost. For infants of informed parents who choose not to adhere to these guidelines, one may either provide medicinal iron drops starting at 6 months of age, or screen for anemia around 6 to 8 months of age.
For children more than 1 year of age, iron-containing foods, such as those listed above, provide iron in sufficient amounts. Supplemental iron is not required unless the diet is lacking in these foods.
(ix) Vegetarian diets. With careful planning, vegetarian diets for infants and children can be nutritionally adequate (Sanders, 1995; Sanders and Reddy, 1994). For vegan infants who are not breastfed, commercially prepared soy-based infant formula is recommended during the first 2 years of life to provide adequate nutrients and energy for growth and development. For older infants, a carefully selected vegetarian diet can meet all the requirements of a growing child; however, deficiencies of iron, vitamin B12, vitamin D and energy have been reported in vegetarian children (Sanders, 1995; Jacobs and Dwyer, 1988). The guidelines presented for introducing solid foods (see Transition to Solid Foods) apply to all healthy infants, including vegans. Parents who feed their infant vegan diets in the first 2 years of life may benefit from consultation with a dietitian or nutritionist to ensure the adequacy of their infant's food (nutrient) intake, and to assess the need for nutrient supplements.
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