The global obesity pandemic has arisen from small imbalances in energy intake and expenditure that have accumulated over time. For primary obesity prevention, the energy gap in the United States is less than 100 kcal/day for 90% of the population, meaning that relatively small changes in energy intake and expenditure adding up to 100 kcal/day could arrest excess weight gain in most people. Preventing further weight gain in the population could substantially reduce the prevalence of obesity within one generation. The energy gap is even smaller in other countries that have done similar analyses. The energy gap for weight reduction and maintenance (ie, obesity treatment) is much larger than 100 kcal/day due to the increased energy demands to maintain a larger body. Thus, the magnitude of behavioral changes required to restore the current population to normal weight is much larger than that required to prevent further weight gain. At this time, efforts to create and sustain such large changes in behavior, either at the individual or population level, have been unsuccessful. Focusing solely on the large energy gap associated with obesity treatment seems unsatisfactory and unhelpful because it overlooks the tangible progress that could be made in the prevention of primary weight gain and it seems tantamount to suggesting that attempts to deal with obesity should only be initiated once it is established. The notion that the obesity pandemic is exclusively due to increased food intake is also not helpful in finding a solution. Although it is certainly easier to find a villain to blame for increased food intake (the food industry) than it is to assign ownership for sedentariness (eg, progress, technology), it ignores the evidence that increased levels of physical activity are essential for effectively balancing energy intake and expenditure at a healthful weight. Restoring conditions under which human physiology evolved and developed mechanisms for balancing energy intake and expenditure will require both finding effective ways to assure a reasonable level of daily physical activity as well as reducing energy intake. At this time, small changes in both intake and expenditure may be sufficient to prevent further population weight gain and support energy balance at a healthful weight. It will take a concerted effort by both public and private interests to accomplish even this goal. Restoring normal body weights among those already obese would likely require more dramatic intervention including pharmacological and surgical treatment. A small-changes approach must be included in public health strategies and in public policies to address obesity. © 2009 American Dietetic Association.