,Brownetal.(1)providemore evidence that the obesity epidemic has arisen fromgradual weight gain in the population produced by verysmall degrees of energy imbalance. The authors followedover 8000 middle-aged women in Australia for more than 5years, from 1996 to 2001. They found that the womengained an average of 0.5 kg/yr. They estimated that thisgradual weight gain represents an accumulation of 10kcal/d. This research supports our previous research show-ing that the average American adult gains 0.45–0.91 kg(1–2 lbs) each year, which would be an average accumula-tion of 15 kcal/d (2). There is an energy cost to storingexcess energy, which we estimated to be 50%, so that theactual degree of energy imbalance causing the weight gainin middle-aged Australian women would be 20 kcal/d andkcal/d. Targeting weight gain prevention is a long-term30 kcal/d in the U.S. adult population. The higher imbal-ance in the U.S. could be because of a more “obesigenic”environment or because the U.S. sample includes a widerrange of adults than the Australian sample (i.e., middle-agedwomen may be gaining weight at a lesser rate than other agegroups).We coined the term “energy gap,” which estimates theexcess daily energy intake over daily energy expenditurethat produces weight gain. Estimating the energy gap canprovide an indication of how much behavior change isrequired to prevent weight gain in any given population. Forexample, we estimated that if we could modify energybalance (any combination of reducing energy intake andincreasing energy expenditure) by 100 kcal/d, we couldprevent weight gain in 90% of the U.S. adult population (2).The implications of this research are that prevention ofexcessive weight gain could be accomplished through smallbehavior changes to “close” the energy gap. We have a poorability to produce and maintain the large behavior changesrequired to treat overweight and obesity. We have a betterchance of producing and sustaining small behavior changesthat may be sufficient to prevent weight gain in most of thepopulation. This small change approach can give us someneeded optimism that we might actually be able to begin toturn the tide on the increasing prevalence of obesity. Afeasible goal is to prevent weight gain in all adults, regard-less of their current weight status. A feasible goal forchildren is to prevent excessive weight gain, which can beidentified for specific groups of children by identifying theenergy gap. Some groups are gaining weight at a higher ratethan others and will have a greater energy gap. For example,Butte et al. (3) have studied a group of low income Hispanicchildren who are highly susceptible to weight gain and haveestimated the energy gap in this group to be 200–250strategy to reduce the prevalence of obesity, but it seems tobe our most feasible strategy given our current inability toproduce and sustain most behavior changes.It is important to realize that any changes in behavior,even small ones needed to close the energy gap, will bedifficult to sustain for the majority of the population unlesswe are able to make changes in the environment to make iteasier for people to maintain the behavior changes. To dothis, we will have to address the way we build communities,the way we market food and physical inactivity, the way weaim policies regarding food and physical activity, and eventhe way our sociocultural beliefs shape our individual andcollective behavior.