In this issue of Obesity Research, Brown et al. (1) provide more evidence that the obesity epidemic has arisen from gradual weight gain in the population produced by very small degrees of energy imbalance. The authors followed over 8000 middle-aged women in Australia for more than 5 years, from 1996 to 2001. They found that the women gained an average of 0.5 kg/yr. They estimated that this gradual weight gain represents an accumulation of ∼10 kcal/d. This research supports our previous research showing that the average American adult gains 0.45–0.91 kg (1–2 lbs) each year, which would be an average accumulation of 15 kcal/d (2). There is an energy cost to storing excess energy, which we estimated to be 50%, so that the actual degree of energy imbalance causing the weight gain in middle-aged Australian women would be ∼20 kcal/d and ∼30 kcal/d in the U.S. adult population. The higher imbalance in the U.S. could be because of a more “obesigenic” environment or because the U.S. sample includes a wider range of adults than the Australian sample (i.e., middle-aged women may be gaining weight at a lesser rate than other age groups).
We coined the term “energy gap,” which estimates the excess daily energy intake over daily energy expenditure that produces weight gain. Estimating the energy gap can provide an indication of how much behavior change is required to prevent weight gain in any given population. For example, we estimated that if we could modify energy balance (any combination of reducing energy intake and increasing energy expenditure) by 100 kcal/d, we could prevent weight gain in 90% of the U.S. adult population (2).
The implications of this research are that prevention of excessive weight gain could be accomplished through small behavior changes to “close” the energy gap. We have a poor ability to produce and maintain the large behavior changes required to treat overweight and obesity. We have a better chance of producing and sustaining small behavior changes that may be sufficient to prevent weight gain in most of the population. This small change approach can give us some needed optimism that we might actually be able to begin to turn the tide on the increasing prevalence of obesity. A feasible goal is to prevent weight gain in all adults, regardless of their current weight status. A feasible goal for children is to prevent excessive weight gain, which can be identified for specific groups of children by identifying the energy gap. Some groups are gaining weight at a higher rate than others and will have a greater energy gap. For example, Butte et al. (3) have studied a group of low income Hispanic children who are highly susceptible to weight gain and have estimated the energy gap in this group to be 200–250 kcal/d. Targeting weight gain prevention is a long-term strategy to reduce the prevalence of obesity, but it seems to be our most feasible strategy given our current inability to produce 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 be difficult to sustain for the majority of the population unless we are able to make changes in the environment to make it easier for people to maintain the behavior changes. To do this, we will have to address the way we build communities, the way we market food and physical inactivity, the way we aim policies regarding food and physical activity, and even the way our sociocultural beliefs shape our individual and collective behavior.