Key messages

• Combining strategies for changing diet and physical activity levels in children aged 2 to 4 years to help prevent overweight and obesity may reduce body mass index (BMI) slightly in the long term (after 15 months).

• There was very little information about whether the strategies resulted in serious adverse events (e.g. injuries), but none of the strategies appeared to result in any serious harm to the children.

• Future research should carry out obesity prevention strategies in community settings, and target the wider determinants of obesity and obesity prevention.

Why is preventing obesity in children important?

There is an increasing number of young children living with overweight and obesity worldwide, with evidence of the rates increasing in line with social inequality. Living with overweight during childhood can cause physical and psychological health problems. Children living with overweight are more likely to live with overweight as adults, and continue to experience poor physical and mental health.

What did we want to find out?

We wanted to find out if strategies to help people change diet or activity (or both) are effective at preventing obesity in children aged 2 to 4 years, and whether they are associated with any serious adverse events. To examine obesity, we used the measure of body mass index (BMI). BMI is calculated by dividing a person's weight (in kg) by their height (in m²).

What did we do?

We searched for studies that looked at ways to prevent obesity in children aged 2 to 4 years. We did not include studies that only targeted children who were already living with overweight or obesity, but we did include studies involving children at a range of weights. We only included studies if they used methods aimed at changing children's diet, activity level (increasing physical activity or reducing sedentary behaviour), or both. We compared and summarised the results of the studies and rated our confidence in the evidence, based on factors such as study methods and sizes. We grouped studies together for analysis depending on whether they aimed to improve diet, activity, or both.

What did we find?

We found 67 studies involving 36,601 children aged 2 to 4 years. Most studies (63 of 67) were based in high-income countries, and four in upper-middle-income countries. In 26 studies, the strategies were conducted in childcare settings, 23 studies were primarily home-based, and 10 were performed in both childcare and home-based settings. Only 3 studies were conducted in the community, and 5 in healthcare settings. The duration of the programmes varied: 47 ran for fewer than 9 months, with the shortest being 1 visit and the longest lasting 3 years. We analysed results from 56 studies involving 21,404 children.

Main findings

• Children who were helped with a strategy to change their diet and activity levels may have had a reduced BMI, compared with children not given any strategy. This means that these children may have been able to minimise excess weight gain by a small amount, which, for public health, is important.

• Children who were helped with a strategy to change their diet or activity alone did not have a reduced BMI.

• Only six of the 67 included studies reported on serious adverse events, and no serious harms were identified.

What are the limitations of the evidence?

Overall, our confidence in the evidence is very low. However, we do not believe that results from more studies similar in design to those included in this review would produce a higher level of confidence in the results.

Four main factors reduced our confidence in the evidence.

• Results were very inconsistent across different studies.

• There were not enough studies reporting specific types of outcomes for a particular duration of follow-up to be certain about the results for some comparisons.

• Results from some studies were not reported in a way that we could include in our analyses and this may have had an impact on the combined results.

• Studies generally had limitations in how they were conducted, due to the complexity of studies in this age group.

This review does not provide enough information to assess how well these strategies work for children with disabilities or those from low- and middle-income countries.

How current is this evidence?

This review updates a previous review. The evidence is current to February 2023.