Aims Given that overweight and obesity are primarily caused by an energy-rich and low nutrient diet which contributes to a positive net energy imbalance, the primary aim of this study was to simulate a range of policy-relevant calorie-reduction interventions to measure the impact on obesity and inequalities.

Methods The predicted probability of obesity at age 11 was estimated using marginal structural models adjusted for total calorie consumption, as calculated from three-day diet diaries at age 7 years, and other baseline and intermediate confounding using data from Avon Longitudinal Study of Parents and Children (n=10,680). Socioeconomic inequalities were indicated using maternal social class and assessed using odds ratios for absolute and relative inequalities. Complete case and multiple imputation analyses were conducted to manage survey attrition and missing data. A series of probabilities were estimated by manipulating the mediator to simulate daily calorie-reduction interventions, including targeted and informed scenarios.

Results Using imputed data and adjusting for inequalities and confounding, 18.3% of children were living with obesity at 11 years. Maternal social class at baseline and total daily calories at 7 years significantly predicted obesity at 11 years. A simulation to reduce intake down to recommended levels, a 6% reduction in daily calories, universally applied but with random variation, reduced overall obesity prevalence by 0.8% with the greatest decrease observed among the lowest social class, meaning this intervention would reduce inequalities. Targeted interventions by income led to variations in reductions by social group. Informed interventions for children with overweight or obesity, or for children who ate excess calories daily, both at age 7 reduced obesity prevalence at age 11 by 0.9% and 1.5% respectively.

Conclusions A universal decrease in total daily calories to the recommended daily limit would reduce childhood obesity and inequalities but disproportionate uptake targeted across SES would have little impact on the overall effect. Informed interventions to reduce caloric intake among children who ate excess calories daily, or with overweight or obese at age 7, would be effective at reducing obesity and inequalities.