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Am Fam Physician. 2020;101(7):394

Author disclosure: No relevant financial affiliations.

Clinical Question

Do dietary and physical activity interventions reduce obesity rates in children?

Evidence-Based Answer

Individual dietary interventions alone fail to change body mass index (BMI) or the standardized BMI z-score (zBMI) across all age groups. The impact of regular physical activity or combined dietary and physical activity interventions is modest at best.1 (Strength of Recommendation [SOR]: C, based on consensus, disease-oriented evidence, usual practice, expert opinion, or case series.)

In children five years and younger, combined dietary and physical activity interventions mildly decrease BMI and zBMI.1 (SOR: C, based on consensus, disease-oriented evidence, usual practice, expert opinion, or case series.)

In children six to 12 years of age, physical activity interventions alone mildly decrease BMI without changing zBMI, whereas combined interventions mildly decrease zBMI without changing BMI.1 (SOR: C, based on consensus, disease-oriented evidence, usual practice, expert opinion, or case series.)

In children 13 years and older, low-quality evidence shows no change in either BMI or zBMI, even when dietary and physical activity interventions are combined.1 (SOR: C, based on consensus, disease-oriented evidence, usual practice, expert opinion, or case series.)

Age group (years)InterventionOutcomeDifferenceStudiesParticipantsEvidence quality
0 to 5DietzBMINot significant1520Moderate
Physical activityzBMI/BMINot significant4/51,053/2,233High
Diet and physical activityzBMIMD = 0.07 lower (95% CI, 0.14 to 0.01)166,261Moderate
BMIMD = 0.11 kg per m2 lower (95% CI, 0.21 to 0)115,536Moderate
6 to 12DietzBMI/BMINot significant6/97,231/5,061High
Physical activityzBMINot significant86,841Moderate
BMIMD = 0.10 kg per m2 lower (95% CI, 0.14 to 0.05)1416,410Moderate
Diet and physical activityzBMIMD = 0.05 lower (95% CI, 0.10 to 0.01)2024,043Low
BMINot significant2519,498Low
13 to 18DietBMINot significant2294Low
Physical activityzBMIMD = 0.20 lower (95% CI, 0.30 to 0.10)1100Low
BMIMD = 1.53 kg per m2 lower (95% CI, 2.67 to 0.39)4720Very low
Diet and physical activityzBMI/BMINot significant6/816,543/16,583Low

Practice Pointers

Obesity in children is defined as a BMI at the 95th percentile or greater on growth charts from the Centers for Disease Control and Prevention (CDC). Childhood obesity rates are increasing, affecting 14% of children in 1999 and 19% in 2016.2 Obesity rates in low- and middle-income families are nearly double those in high-income families.2 Obesity rates among Hispanic and black children are more than double those in Asian children and nearly double those in non-Hispanic white children.2 The authors of this review sought to characterize the effect of lifestyle interventions to prevent childhood obesity in different age ranges.

This Cochrane review included 153 randomized controlled trials with 51,946 patients.1 Studies were heterogeneous in population, interventions, and duration. Nearly 90% of studies were from the United States and Europe, and more than 60% of studies evaluated a combination of dietary and physical activity interventions. More than one-half were conducted in school or day care settings, 14% of which had a family component, and 9% were conducted in homes. Populations studied varied from all children to only overweight or obese children. Interventions included education, health promotion, and family or behavioral therapy. Studies were conducted for a minimum of three months with only 24% of studies exceeding 12 months and only 8% exceeding two years. No adverse effects, including an increased rate of underweight children, were reported from any intervention.

The results of interventions were measured as changes in BMI or zBMI, with more than one-half of studies using BMI. zBMI is commonly used to measure obesity in children while correcting for variation in average BMI with age. CDC growth charts are developed using a modified zBMI, and both BMI and zBMI are inaccurate for evaluating severe obesity, in which the BMI exceeds the 97th percentile.3 Changes in zBMI approximate changes in BMI.

In children five years and younger, neither dietary nor physical activity interventions alone improved obesity measures. Combined dietary and physical activity interventions led to an average decrease in BMI of 0.11 kg per m2 (95% CI, 0.21 to 0) and an average decrease in zBMI of 0.07 (95% CI, 0.14 to 0.01). These results were driven by three studies of home interventions that reduced BMI and zBMI, whereas eight studies of day care interventions showed no effect. The effective home studies were implemented by pediatricians, nurses, or health educators and were six months to two years in duration.

In children six to 12 years of age, physical activity interventions led to an average decrease in BMI of 0.10 kg per m2 (95% CI, 0.14 to 0.05) without a change in zBMI. Dietary interventions alone were ineffective. Combined dietary and physical activity interventions led to an average decrease in zBMI of 0.05 (95% CI, 0.10 to 0.01) without a change in BMI. Interventions were effective if they were conducted in school or lasted up to 12 months. No home interventions were conducted in this age group.

In children 13 years and older, physical activity interventions alone led to an average decrease in zBMI of 0.20 (95% CI, 0.30 to 0.10) and in BMI of 1.53 kg per m2 (95% CI, 2.67 to 0.39) in small, low-quality, short-duration studies performed at school. Larger, higher-quality studies of combined dietary and physical activity interventions conducted in various settings failed to demonstrate benefit. No home interventions were conducted in this age group.

Guidelines from the Department of Health and Human Services recommend at least an hour per day of moderate-intensity aerobic physical activity for all children.4 Similarly, the National Institute for Health and Care Excellence recommends 60 minutes of moderate to intense aerobic exercise each day and states that dietary modifications alone are insufficient to prevent obesity.5 The limited evidence presented in this review supports combining dietary and physical activity interventions given the benefits for reducing childhood obesity. Interventions did not increase health inequalities and could temper existing inequalities.

The practice recommendations in this activity are available at http://www.cochrane.org/CD001871.

Editor's Note: Dr. Arnold is a contributing editor for AFP.

The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Department of the Navy, Department of the Army, Uniformed Services University of the Health Sciences, Department of Defense, Department of Veterans Affairs, or the U.S. government.

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