Exploring intervention fidelity in trials of interventions to change infant feeding behaviours – are we testing what we think we’re testing?


The first two years of life represent an important stage in a child’s development. In particular, how and what a child is fed during this time has an important influence on their subsequent development. For example, infant feeding behaviours such as the early or inappropriate introduction of solid foods into a child’s diet have been associated with the later development of childhood obesity [1, 2]. Childhood obesity is an urgent global concern, with serious health, economic and social implications both for the individual and the wider health system. Therefore infant feeding behaviours represent a potential target for the prevention of childhood obesity and a worthwhile focus for behaviour change intervention research.

To date, studies have found that the effectiveness of infant feeding interventions to prevent childhood obesity to be somewhat variable and inconsistent [3, 4]. However, little is known about the actual implementation of the interventions within these trials, and the ‘fidelity’ with which they were put into practice. Intervention fidelity refers to the extent to which an intervention is actually implemented as intended by the researchers who designed it [5]. For example, are all aspects of the intervention delivered by the providers as planned? Do participants actually attend or engage with the intervention, do they receive or use intervention materials or resources as intended? Intervention fidelity is an important methodological aspect of behavioural studies, as without knowledge of intervention fidelity we are only really assuming that the intended intervention is being tested.

In a recent systematic review [6], we explored the use and reporting of different strategies to enhance and assess intervention fidelity within trials of infant feeding interventions delivered by healthcare professionals to prevent childhood obesity. We also explored the associations between fidelity score and study quality, intervention effectiveness and publication year. Using a systematic search strategy we identified 10 trials represented in 16 papers. Across these studies, the average use and/or reporting of strategies to enhance (e.g. training manuals/protocols) and/or assess intervention fidelity (e.g. delivery checklists) was moderate (54%), ranging from 28.9% to 76.7%. No patterns were observed between levels of fidelity reporting/use and study quality, effectiveness or publication year. Interestingly, although six studies reported using a method to assess fidelity of intervention delivery, only 2 studies explicitly reported the results of this fidelity assessment.

The moderate use/reporting of fidelity strategies within trials of infant feeding interventions identified in our review suggest that previous findings of inconsistent effectiveness may not fully reflect the intended interventions. As a result, our study identified a number of recommendations that could improve the methodological quality of future trials of infant feeding interventions, to ensure that these trials are a more accurate test of the intervention in question. These include 1) ensuring adequate focus on how intervention providers are trained and the knowledge and skills needed to deliver the intervention as intended, 2) ensuring adequate focus on the fidelity of treatment within comparator or control groups and 3) ensuring better reporting across all aspects of fidelity, in particular the results of fidelity assessments. In doing so, improved intervention fidelity will facilitate better interpretation and understanding of the findings of such trials, and provide more information to support the translation of successful interventions into policy and practice.


Dr. Elaine Toomey,

HRB Interdisciplinary Capacity Enhancement (ICE) Postdoctoral Research Fellow, Health Behaviour Change Research Group/Associate Director of Cochrane Ireland with Evidence Synthesis Ireland

National University of Ireland, Galway


Dr. Toomey wrote this piece on behalf of the CHErIsH Choosing Healthy Eating for Infant Health study team. The CHErIsH study is a Health Research Board funded project to develop and evaluate an intervention to improve infant feeding behaviours in primary care. For more information see www.cherishstudy.com.’


  1. Woo Baidal JA, Locks LM, Cheng ER, Blake-Lamb TL, Perkins ME, Taveras EM: Risk Factors for Childhood Obesity in the First 1,000 Days: A Systematic Review. Am J Prev Med. 2016;50:761-779.
  2. Pluymen LPM, Wijga AH, Gehring U, Koppelman GH, Smit HA, van Rossem L: Early introduction of complementary foods and childhood overweight in breastfed and formula-fed infants in the Netherlands: the PIAMA birth cohort study. Eur J Nutr. 2018;57:1985-1993.
  3. Matvienko-Sikar K, Toomey E, Delaney L, Harrington J, Byrne M, Kearney PM: Effects of healthcare professional delivered early feeding interventions on feeding practices and dietary intake: A systematic review. Appetite. 2018;123:56-71.
  4. Redsell SA, Edmonds B, Swift JA, Siriwardena AN, Weng S, Nathan D, Glazebrook C: Systematic review of randomised controlled trials of interventions that aim to reduce the risk, either directly or indirectly, of overweight and obesity in infancy and early childhood. Maternal & Child Nutrition. 2016;12:24-38.
  5. Bellg AJ, Borrelli B, Resnick B, Hecht J, Minicucci DS, Ory M, Ogedegbe G, Orwig D, Ernst D, Czajkowski S: Enhancing treatment fidelity in health behavior change studies: best practices and recommendations from the NIH Behavior Change Consortium. Health Psychol. 2004;23:443-451.
  6. Toomey E, Matvienko-Sikar K, Heary C, Delaney L, Queally M, B Hayes C, M Kearney P, Byrne M, Choosing Healthy Eating for Infant Health study t: Intervention Fidelity Within Trials of Infant Feeding Behavioral Interventions to Prevent Childhood Obesity: A Systematic Review. Annals of Behavioral Medicine. 2018:kay021-kay021.