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4 October 2004
Portion Size A Big Contributor To Weight Gain 
Cornell University researchers have found that when young adults are served larger portions from one week to the next, they overeat by almost 40%. The research, appearing in the Journal of Nutrition, suggests that larger portions over time could account for the growth of the American girth over the past 20 years. "The more food we served to the college-student volunteers in our eating study, the more they ate," says David Levitsky, professor of nutritional sciences at Cornell. "Since we know that restaurants are serving larger and larger food portions, we think that larger portions could be a major factor responsible for the increase in overweight and obesity that is so evident today." The study volunteers who consumed the largest portions - portions 150% larger than the week before - ate an average of 39% more food, in weight, during the week than they did the previous week, an average of 273 more calories per person. Studies by other researchers have shown that while Americans, on average, are not using up as many calories through exercise today compared with 20 years ago, they are taking in about 200 more calories a day than they did in the 1970s. Researchers report that almost half of Americans' meals are now consumed outside the home, and that restaurant portion sizes have jumped by between 20% and 60% over the past 20 years. Another study found that 35% of 181 food products reviewed jumped in size between the 1970s and 1999. Meanwhile, the prevalence of adult obesity in the United States jumped to almost 31% of the population in 1999 from 14% in 1971. This new research suggests larger portions play an important role in the obesity epidemic. Levitsky says his studies have shown that the size of breakfast or between-meal snacks does not affect the amount consumed at subsequent meals. "Likewise, if you don't eat for a day, you rate yourself more hungry, but you don't eat more food the next day. We've also shown that when you are fed and eat 33% (above normal portions) per day for two weeks, the day after you stop overeating, you rate yourself as full, but again, you eat the same amount of food as you did prior to the overfeeding. From a public health perspective, the results of this study are extremely encouraging," Levitsky concludes. "If it's correct that the increase in portion size is a major cause of the epidemic of obesity, then it should be possible to stop, and possibly reverse, this trend toward increased body weight by taking control of size of portions served."
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