Fast food’s high energy density, good taste, high fat content, low fiber content, and high content of refined starches and sugars all contribute to weight gain. Despite regular fast food consumption, however, not all adolescents gain weight. Ebbeling and colleagues hypothesized that lean adolescents who regularly consume fast food eat less afterward than overweight adolescents.

To test this hypothesis, the authors recruited 54 lean and overweight adolescents 13 to 17 years of age for two studies. The first study took place in an observational setting to determine fast food consumption as it might occur in real life. The second study compared energy intake on the days fast food was consumed with intake on the days it was not consumed.

In the first study, the enrollees were fed a fast food meal at a national fast food chain restaurant. Participants were grouped by sex and weight and were given as much as they liked of standard weight servings, with refills supplied immediately as needed. After finishing the meal, participants were asked to estimate the size of their meal on a visual analogue scale, while each person’s actual consumption was measured, with gram weight converted to energy units.

In the second study, 51 adolescents from the first study were interviewed on two fast food days (defined as eating from one of five fast food chains and including one meat item) and two non–fast food days and were asked to recall their food intake and physical exercise on that day.

In the “natural” fast food eating session, overweight participants ate more than lean participants in absolute terms and relative to the individual’s daily energy requirements. In the second study, overweight participants ate 409 kcal per day more on fast food days than on non–fast food days, whereas the lean participants ate the same amount as always on days they ate fast food.

Assuming an average energy consumption of about 790 kcal per meal to maintain energy requirements, enrollees greatly overate at their trial fast food meal, consuming about 1,652 kcal, or two thirds of the daily energy requirement. Overweight teens ate more than their lean counterparts and consumed more overall on fast food days than non–fast food days, compared with lean participants, who ate the same amounts whether it was a fast food day or not.

The authors conclude that the lean participants ate less at other meals on days they ate fast food meals, while the overweight participants did not compensate at other meals by eating less. It is not clear whether the failure to compensate in the overweight group is a primary cause of obesity related to a genetic propensity or if it results secondarily from being overweight. It also was found that overweight teens underreported the amount that they ate compared with lean adolescents.