Dietary prevention of allergic disease in children: are current recommendations really based on good evidence?

We provide a critical appraisal of the literature on the effects of dietary prevention of atopic disease in children. In our view, currently available studies suffer from lack of blinding which is a major problem if the primary end point is subjective (such as the diagnosis of eczema). In addition, long-term follow-up suggests that atopic symptoms are delayed rather than truly prevented, and that only the mildest cases are prevented (or delayed). Although it has been reported that cow's milk allergy is truly prevented by dietary interventions in early life, this has never been demonstrated by double-blind placebo-controlled food challenges. No studies to date have shown effects of hypoallergenic formulae on objective markers of atopic sensitization, such as specific IgE levels. Finally, there is no universally accepted pathophysiological mechanism which could explain the usefulness of hypoallergenic formulae in allergy prevention. In conclusion, we feel that the currently available evidence on the allergy preventive effects of hypoallergenic formulae is insufficient to justify blanket advice being given to 'high risk' families. Such advice gives parents the hope that they can actually prevent allergy in their children which may not be justified. A cautious approach in advising interventions with hypoallergenic formulae to prevent allergy in high-risk infants is warranted.

Omega-3 and omega-6 fatty acid exposure from early life does not affect atopy and asthma at age 5 years

BACKGROUND

The Childhood Asthma Prevention Study was a randomized controlled trial conducted in children with a family history of asthma in whom omega-3 fatty acid supplementation and restriction of dietary omega-6 fatty acids did not prevent asthma, eczema, or atopy at age 5 years.

OBJECTIVE

We sought to examine the relation of all measures of omega-3 and omega-6 polyunsaturated fatty acids with outcomes at age 5 years in the whole birth cohort, regardless of randomization group.

METHODS

Plasma fatty acids were measured at 18 months, 3 years, and 5 years. Compliance with the fatty acid supplements was estimated every 6 months. Dietary intake was assessed at 18 months by means of weighed-food record and at 3 years by means of food-frequency questionnaire. At age 5 years, 516 children were examined for wheeze and eczema (questionnaire) and atopy (skin prick tests, n = 488). Multiple logistic regression was used to evaluate associations between exposures and outcomes.

RESULTS

Plasma levels of omega-3 or omega-6 fatty acids were not associated with wheeze, eczema, or atopy at age 5 years (P = .11-.96). Overall, fatty acid exposure, measured as plasma levels, dietary intake, and compliance with supplements, was not associated with any respiratory or allergic outcomes (P = .35-.59).

CONCLUSION

This observational analysis of the cohort, using the full range of observed variation in omega-3 and omega-6 fatty acid exposure, supports the negative findings of the randomized controlled trial.

CLINICAL IMPLICATIONS

Modification of dietary polyunsaturated fatty acids in early childhood is not helpful in preventing atopy and asthma.

The concept of hypoallergenicity for atopy prevention

Infancy represents the period in which an individual may be at the highest risk of sensitization. During the first year of life around 2.5% of neonates experience hypersensitivity reactions to cow's milk protein, which is highly associated with early exposure to cow's milk. Attempts to avoid sensitization in this very early period of life and to prevent allergic diseases focus on diets with reduced allergenicity and possibly on the induction of oral tolerance. Hydrolyzed infant formulas are characterized by a reduced allergenicity and thus recommended as substitute or supplementary to breastfeeding during the first 4-6 months of life for infants at high risk of developing atopic diseases. This concept of hypoallergenicity has been shown effective in clinical studies. Both partially and extensively hydrolyzed formulas have demonstrated a potential in protecting from allergic diseases, mainly atopic eczema and food allergy. The in vitro characterization of allergenicity by the degree of hydrolyzation and peptide size, however, does not necessarily predict the immunogenic effect in humans, as it could be shown that the preventive effect seems to be dependent on the process rather than on the degree of hydrolyzation, which could be best explained by a possible production of tolerogenic epitopes.

Probiotics for atopic diseases

One suggestion for why some people develop atopic diseases, such as allergic rhinitis, asthma and atopic eczema, is that there are alterations in their intestinal microflora not seen in those without such conditions. This idea underlies the proposal that probiotics (orally administered micro-organisms) containing, for example, Lactobacillus and Bifidobacterium species, might help to prevent and treat atopic disorders by altering intestinal microflora. We have recently reviewed the use of probiotics for gastrointestinal disorders. Here, we look at whether they have a place in the prevention and treatment of atopic diseases.

Diet and asthma: has the role of dietary lipids been overlooked in the management of asthma?

OBJECTIVE

This article discusses the role of diet in the management of asthma. Readers will gain an understanding of how evolution of the western diet has contributed to increased asthma prevalence and how dietary modification that includes management of dietary lipids may reduce symptoms of asthma.

DATA SOURCES

Relevant studies published in English were reviewed.

STUDY SELECTION

Medline search to identify peer-reviewed abstracts and journal articles.

RESULTS

Asthma and obesity, which often occur together, have increased in prevalence in recent years. Studies suggest adaption of a western diet has not only contributed to obesity, but that increased intake of specific nutrients can cause changes in the frequency and severity of asthma. Increased asthma prevalence has also been proposed to arise from increased exposure to diesel particles or lack of exposure to infectious agents or endotoxins during childhood, generating a biased Th2 immune response, and increased cytokine and leukotriene production. Antagonists directed against these pro-inflammatory mediators include anticytokines and antileukotrienes. A reduction in the levels of inflammatory mediators associated with asthma has also been seen with dietary interventions, such as the administration of oils containing gamma-linolenic acid and eicosapentaenoic acid.

CONCLUSIONS

Evidence suggests elevated body mass index and dietary patterns, especially intake of dietary lipids, contribute to symptoms of asthma. Dietary modification may help patients manage their asthma as well as contribute to their overall health.

Probiotics: on-going research on atopic individuals

The challenge for the modern health care system is to fight against the increasing prevalence of atopic disease. The introduction of scientifically composed probiotic functional foods for prophylactic or therapeutic purposes could be one solution. Probiotics are live microbial food supplements or components of bacteria which have beneficial effects on human health. Specific strains have been demonstrated to exert powerful anti-pathogenic, anti-inflammatory and anti-allergic effects. The hygiene hypothesis suggests that atopic disease may arise from a lack of counterbalancing microbial exposure at an early age. The initial compositional development of the gut microflora is considered a key determinant of the development of both the immune responder phenotype and normal gut barrier functions. The regulatory role of probiotics in human allergic disease was first emphasised in the demonstration of a suppressive effect on lymphocyte proliferation and interleukin-4 generation in vitro. Subsequently, a significant improvement in the clinical course of atopic eczema was reported in infants given a probiotic-supplemented diet. The potential of probiotics to reduce the risk of atopic disease has recently been demonstrated in a double-blind, placebo-controlled study: probiotics administered pre- and postnatally for 6 months to at-risk subjects reduced the prevalence of atopic eczema to half of that observed in infants receiving placebo. Ongoing research is directed towards the development of novel techniques to characterise the gut microflora. Future research will clarify the mechanisms to control specific physiological processes in the evolution of atopic disease in at-risk populations or in the management of allergic diseases.

[Influence of diet during pregnancy and the coexistence of allergy during the 1st year of life]

Thirty atopic pregnant women by clinical history, skin testing, and laboratory data, and 10 non-atopic women, were studied for the influence of a diet on the outcome of their babies. The atopic women were divided into two groups: non-diet and diet group, the last group, decided to follow a non-allergenic diet that they started after 11 weeks of pregnancy. We had a follow up of the babies from all pregnancies after birth for a year. As a part of the babies clinical history, we determined the IgE concentration within 2 months after birth. Our data indicated that two babies from diet group and non from the control group, had an atopic disease during the first year of life, in contrast, five babies from the non-diet group, these preliminary results, suggested that a non-allergenic diet in atopic pregnant women, may decrease the morbidity of atopic disease during the first year of life.

Influence of dietary manipulation on incidence of atopic disease in infants at risk

Of 5,500 newborn infants whose family histories were screened, 900 were found to have anamnestic risk. Cord-blood IgE was evaluable in 4,677 of these newborns, of which 394 had levels > or = 1 IU/mL; 84 infants had both anamnestic risk and elevated cord-blood IgE levels. Parents of infants with anamnestic risk were informed of their child's risk of atopy. Additionally, for 391 infants at two of the three participating hospitals, a preventive diet was prescribed that recommended breastfeeding for the first 6 months of life, with maternal diet restricted to no more than 200 dL of cow milk per day, no more than one egg per week, and no tomato, fish, shellfish, nuts, or foods allergenic to the mother. Only soy formula was recommended, and introduction of solid foods was also carefully prescribed. Furthermore, doctors recommended against exposure to tobacco smoke, animal allergens, and early entrance into daycare. Evaluable infants whose parents complied with the prescribed diet were found to have a lower incidence of atopy during the first year of life (13.3%, n = 158) than infants whose parents had ignored the prescribed diet (54.7%, n = 86) or infants whose parents were offered no dietary recommendations (28.9%, n = 218). Differences between the compliant group and the two groups with unrestricted diets were significant, indicating that this prescribed diet may protect against or delay onset of food allergies during the first year of life.

A double-blind comparison of olive oil and a combination of evening primrose oil and fish oil in the management of canine atopy

A randomised double-blind parallel study lasting eight weeks was used to assess the effects of olive oil in a group of atopic dogs whose clinical signs were well controlled by dietary supplementation with a combination of evening primrose oil and fish oil. Nine of the 11 dogs which continued to receive this combination were considered unchanged at the conclusion of the study, whereas eight of the 10 dogs switched to olive oil had deteriorated. The mean plasma concentration of dihomogammalinolenic acid, a precursor of potentially antiinflammatory mediators, was significantly reduced (P < 0.05) in the olive oil-treated group at the end of the study. There were no significant differences between the mean plasma linoleic, eicosapentaenoic and arachidonic acid concentrations in the two groups. These findings suggest that olive oil is not an effective therapeutic agent in the control of canine atopy.

Definitions and diagnosis of food intolerance and food allergy: consensus and controversy

This article describes the terms used for the various syndromes and diseases associated with reactions to foods; it outlines the principal types of food intolerance encountered in children, with particular emphasis on those caused by immune-mediated reactions of immediate hypersensitivity. Terms defined include food intolerance or food sensitivity; food allergy or food hypersensitivity; psychologically based food reactions (food aversions); and psychosocial and neurologic dysfunction. The spectrum of food sensitivity is considerable, and diagnosis is generally based on the monitoring of effects of exclusion diets and provocation tests, after appropriate objective measures are first selected. In children, manifestations of IgE-mediated food allergy (often in association with other immune mechanisms) include self-limiting and immediate reactions (e.g., urticaria, wheeze) and chronic diseases (food-sensitive enteropathies, eczema). Controversial and unresolved issues exist with some other conditions, including eosinophilic gastroenteritis, occult gastrointestinal bleeding, protein-losing enteropathy, and attention deficit disorder with hyperactivity. New methods for clinical investigation of gastrointestinal tract function and intestinal immune reactions are required to assess the relevance of foods in these conditions.

Possible consequences of elimination diets in asymptomatic immediate hypersensitivity to fish

The natural history of IgE antibodies to food without related symptoms is unknown. We have followed the progress of 7 children with various atopic diseases and asymptomatic immediate hypersensitivity to fish, treated with elimination diet in spite of full alimentary tolerance. During the diet period, between 24 and 113 months, all 7 patients presented immediate symptoms upon accidental exposure to or challenge tests with fish (skin symptoms in all 7 cases, digestive in 5, respiratory in 4, and anaphylaxis in 2), which differed from those related to atopic diseases previously present. The levels of fish-specific IgE (prick test, RAST) remained unchanged or were increased. These findings suggest that during elimination diet, and perhaps due to minimal and hidden contact with the allergen, the patients' degree of sensitization may increase, turning an asymptomatic into a symptomatic immediate hypersensitivity.

Compliance with a dietary manipulation programme in families with infants prone to atopy

The success of familial compliance with a dietary manipulation programme was studied prospectively in 91 newborn babies from atopic families for up to 12 months. The control group consisted of 72 infants from non-atopic families. The percentages of infants breast-fed at the age of six months were 58% and 38% in the study group and control group, respectively. The introduction of cow's milk based formulas was postponed until the age of three months in 63% of the infants in the study group and 47% of the infants in the control group. Solid food was avoided during the first three months in 76% and 45% of the infants in the study group and control group, respectively. Maternal age, smoking and low social class were associated with poor compliance. The existence of atopic dermatitis in any member of the family was associated with good compliance. The main advantages of our programme were the increased number of children breast-fed until the age of six months, and the reduced number of infants introduced to cow's milk based formulas or solid food before three months of age.

Development of atopic disease in babies whose mothers were receiving exclusion diet during pregnancy--a randomized study

In a prospective, randomized study, we have monitored the effect of maternal abstention from cow's milk and egg on the development of atopy in babies. Two hundred twelve women were followed from midpregnancy. We report the occurrences of allergies in their babies up to 18 months of age, as assessed by skin prick testing, determination of serum IgE, questionnaires, and blinded physical examination by a pediatric allergist. Whatever the method that was used, there was no statistically significant difference between babies whose mothers received the "diet" or the "nondiet." Other factors known to influence the risk of atopy like heredity, sex, month of birth, breast-feeding, and exposure to tobacco smoke, animal dandruff, and solid food did not differ between the groups. The mothers receiving the exclusion diet, by their own choice, had diminished their intake of milk and egg during lactation also, and therefore, their babies were significantly less exposed to cow's milk before 6 months. Still, atopy was equally abundant among their children. Thus, maternal elimination diet during late pregnancy did not protect the baby against allergy.