Adequate nutrients early in life promote cognitive development and are critical for proper growth and functioning. The effect of individual nutrients consumed through food is often not the same as consuming the same nutrients in supplementary form due to 'food synergy', the biological and chemical interrelations that occur between nutrients. Animal-source foods, such as eggs, meat, fish, and dairy, are energy dense and contain multiple micronutrients and essential fatty acids with high bioavailability. The benefits of animal-source foods may include higher food synergy relative to fortified foods as well as decreasing dependence on external suppliers of fortified foods.
To assess the effectiveness of animal-source foods compared to any other feeding interventions or no intervention in improving growth and developmental outcomes in children aged 6 to 59 months.
We searched CENTRAL, MEDLINE, Embase, CINAHL, 18 other databases, and three trials registers up to August 2018. We also contacted authors and known experts in the field for assistance in identifying ongoing or unpublished data, and searched the reference lists of included studies and reviews, and websites of relevant organizations, for other studies that may not have been captured by our electronic searches.
We included randomized controlled trials and quasi-randomized controlled trials of any duration, where children between 5 months and 59 months (6 years) of age were provided with an animal-source food (e.g. consumption of milk, meat, or eggs), prepared with any cooking method, compared with any intervention or no intervention.
DATA COLLECTION AND ANALYSIS:
Two review authors independently assessed trial eligibility using prespecified criteria, extracted data, assessed risk of bias, and graded the quality of the evidence using the GRADE approach.
Study characteristicsWe included 6 studies that analyzed data from 3036 children aged 5 to 50 months. The studies were conducted in China, the Democratic Republic of Congo, Ecuador, Guatemala, Pakistan, the USA, and Zambia, and lasted between 5 and 12 months. Three studies were funded, in part, by government entities; one study was supported by a nonprofit organization. Two studies did not report a funding source.Three studies compared the effects of feeding an animal-source food with a fortified (iron or iron and zinc), or unfortified cereal; two used a control group with no intervention; one compared a meat-based diet to a dairy-based diet. The types of animal-source foods tested included yogurt, eggs, cheese, lyophilized (freeze-dried) beef product, ground and frozen pork, puréed and jarred beef with gravy or pork, and powdered whey protein.We judged four studies to be at unclear risk of bias overall; three studies because they were funded by an industry with a plausible interest in the outcome of the intervention; and one study because there was insufficient information to assess five of the seven bias 'Risk of bias' domains. We judged two of the six studies to be at high risk of bias overall; one study because there was significant baseline imbalance in length-for-age z scores (LAZ) between groups and evidence of selective reporting; the other study because there there was both a significant baseline imbalance in LAZ and weight-for-age z scores (WAZ) between groups, and a large-scale social media campaign that may have influenced care received at home in the control group.Key resultsAnimal-source foods versus cereal-based foods or no interventionFive studies (2972 children) measured change in linear growth with either height-for-age z scores (HAZ) or LAZ. Three studies (592 children) reported a significant increase in HAZ and LAZ in the intervention group compared to the control group. Two studies (2380 children) reported a decline in LAZ in both groups. In one study (1062 children) there was no difference between the groups in the rate of decline; in the other (1318 children) the decrease in LAZ was significantly smaller in the intervention group.Five studies (2972 children) measured weight gain using WAZ. Three studies (592 children) reported a significant increase in WAZ in the intervention group compared to the control group. In two studies (2380 children), WAZ decreased in both groups. In one of these studies (1318 children), the decrease in the intervention group was significantly smaller than in the control group. In the other study (1062 children), there was no difference between the groups.Three studies (1612 children) reported impacts on all-cause morbidity, but metrics were inconsistent between studies. One study with yogurt (402 children) reported a significant reduction in duration and incidence of diarrhea and upper respiratory infections in the intervention group. One study with eggs (148 children) reported a significant increase in the incidence of diarrhea in the intervention group, but this may have been due to cultural associations with eggs and gastrointestional problems. There were no other significant differences in fever, respiratory infections, or skin conditions between groups. The third study (1062 children) found no differences between intervention and control groups across morbidity measures.No studies reported data on anemia.Meat-based diet versus dairy-based dietOne study (64 children) measured change in LAZ and WAZ in infants fed either a meat-based diet or dairy-based diet. There was a significant increase in LAZ among infants consuming the meat-based diet and a significant decrease in LAZ among infants consuming a dairy-based diet. WAZ increased in both groups, with no significant difference between groups.The study did not assess all-cause morbidity or anemia.Quality of the evidenceWe rated the quality of the evidence as very low overall due to baseline imbalances between intervention and control groups, high heterogeneity in meta-analysis, and imprecision due to wide confidence intervals and inconsistent direction of effects. We have little confidence in the results; further research is likely to change the estimate of magnitude and direction of treatment effect.
Given the limited quality of the evidence, we are uncertain of the effects of the provision of animal-source food versus cereal products or no intervention on the growth or development of children. More adequately powered trials with deliberately selected animal-source foods are needed.
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