(The following passage is excerpted from an article published in the Journal of the American Dietetic Association in 2003.)Obesity (including overweight) is the principal public health nutrition problem in the United States, largely because of its ability to increase chronic disease risk and its increasing prevalence among adults and children. The rapidity of the increase is startling. The prevalence has increased sharply just within the past decade, and the increase is occurring so quickly that statewide changes can be mapped from one year to the next. We know that the cause is excess energy (calories) consumed over energy expended in daily activities, and that to lose weight, people must consume fewer calories or expend more. Levels of physical activity do not seem to have declined during the past decade, which means that the obesity epidemic must be caused by increased caloric intake. At issue is the cause of this increase. Most commentators attribute the change to lifestyle patterns (women working outside of the home, longer working hours, need for convenience) or to personal dietary preferences for foods high in fat, sugar, and salt. Only recently have investigators focused attention on changes in the food system—production, marketing, and government policies—that might promote excessive energy consumption. They point out that one result of our overabundant (and, therefore, overmarketed) food supply is an increase in the amounts of food sold and consumed at any one time. Larger portions have more calories, and people tend to eat more when confronted with large amounts of food. But are portions really getting larger, or is that idea just an impression fostered by articles in the popular press?Such questions prompted Lisa Young, PhD, RD, to measure the actual size of food portions sold as single servings in convenience stores, fast-food establishments, and chain restaurants as part of her doctoral research. Her findings clearly showed that portion sizes of many such foods increased since the mid-1980s and, consequently, increased in calories. In this issue of the Journal, Smiciklas-Wright and colleagues extend these findings in a systematic comparison of the results of the 1989–1991 and 1994–1996 Continuing Surveys of Food Intakes by Individuals (CSFII). These US Department of Agriculture (USDA) surveys collected 24-hour recall lists from more than 11,000 individuals on three separate days. Respondents reported consuming larger portions of nearly one-third of the 107 foods examined, just within this 5-year interval. They reported increases in the portion sizes of bread, crackers, cookies, cereals, pasta, french fries, beer, wine, fruit juices and drinks, and, not least, soft drinks. In contrast, they reported other food portions as having decreased: rice, macaroni and cheese, pizza, carrots, bacon, chicken, margarine, and mayonnaise. How are we to interpret such results? The investigators point out that the methods used to collect data in the two CSFII surveys differed and that all such methods are "difficult and subject to inaccuracies." This understates the problem; respondents to dietary surveys tend to underreport foods they think are bad and overreport foods they think are good. The decline in portion size for pizza, for example, could reflect underreporting, because it is inconsistent with measured increases in the sizes of marketplace pizza slices; and many people think of pizza as a fattening food. Although the investigators find sharp increases in the sizes of beverage portions, the increasing size of soft drink serving cups suggests that these results also could be underestimates. From the data in this article and in standard food composition tables, I estimate that CSFII respondents reported increases in the portion sizes of orange juice by about 1 ounce (15 kcal), of soft drinks by 2 ounces (25 kcal), of fruit drinks by 2 ounces (30 kcal), of wine by about 1.5 ounces (30 kcal), and of beer by an astounding 8 ounces (96 kcal). Although these numbers are not large (except for beer), an increase of 25 kcal/day from soft drinks alone comes to more than 9,000 kcal per year—an amount approaching a 3-pound weight gain. Even if the decreases reported for some foods are correct, they are more than offset by the larger number of portions reported as having expanded in that 5-year period. In the last sentence of the first paragraph ("Levels of . . . intake"), the author’s commentary about physical activity serves to:A) illustrate a factor that can reduce chronic disease risk. B) help explain the rapidity with which obesity rates are increasing. C) provide evidence for a previous assertion about the cause of obesity. D) eliminate a possible explanation for the increase in obesity rates. E) suggest that exercise and diet are not necessarily interdependent.