'Portion distortion' may contribute to expanding waistlines, study reports

Growing portions over last two decades may confuse consumers about appropriate serving sizes

NEW BRUNSWICK, NJ New research shows that people's perceptions of normal portion sizes have changed in the past 20 years. A study out of Rutgers published in the September issue of the Journal of the American Dietetic Association reports that Portion Distortion may be the cause1. This phenomenon occurs when consumers perceive large portion sizes as appropriate amounts to eat at a single eating occasion.

"It has previously been established that portion sizes of virtually all foods and beverages served at restaurants and packaged for single-serve have dramatically increased over the last two decades," said Jaime Schwartz MS, RD, who was a graduate student at Rutgers at the time of this study. "Our study compared what people perceive to be a typical portion size now to what was perceived as typical two decades ago, before portions began to grow. We also compared current perceptions of typical portions to reference portion sizes, defined in this study as the serving size on the Nutrition Facts panel."

This study replicated one that was done 20 years ago in which participants were asked to serve themselves the amount they considered to be a typical portion of each meal item on a buffet table2. To follow this model, Schwartz and co-author, Carol Byrd-Bredbenner, PhD, RD, enrolled 177 young adults to participate. All were invited to attend one meal, selecting typical portions of a total of eight meal items at breakfast or six at lunch and dinner. Food and beverage choices mirrored the study of 20 years ago as to permit valid comparisons between typical portions over time.

Portions Are Distorted

Interestingly, most foods with drastically different portion sizes over the two decades were all served from and consumed from a cup or bowl. For example, typical portions of orange juice were more than 40 percent larger in the present day study than they were 20 years ago. In nutritional terms, this larger amount of orange juice provides 50 additional calories and could equal a five pound weight gain over the course of one year if consumed on a daily basis. Participants in the present study served themselves nearly 20 percent more cornflakes and poured almost 30 percent more milk on their cereal than participants 20 years ago.

On average, less than 45 percent of portions selected at the breakfast meal were within 25 percent of the reference portion size. For the lunch and dinner meals, around 30 percent of portions were within 25 percent of the reference portion size. This strongly suggests that the amount of food thought to be appropriate to eat at one sitting is different than what the Nutrition Facts panel indicates to be a single serving size. "With portions being distorted to this degree, it's no surprise that people's waistlines are expanding." Byrd-Bredbenner remarked.

Nutrition Education May Serve Well

The good news is that efforts to educate the public to limit certain foods that add excess calories may have been successful. For example, the typical portion size of salad dressing was significantly smaller in the current study than typical portions selected in the study done 20 years ago. The message that even nutritious foods (e.g., tossed salad) can become less healthy when calorically dense items (e.g., salad dressing) are used excessively, may have become well understood over the past two decades.

Although the causes of obesity are multifactorial, the incidence of obesity has increased over the past two decades in parallel with increasing portion sizes, and Portion Distortion may be a contributing factor. "Our society wants the 'bang for our buck' and when portions are served to us that we think are small we feel short-changed," commented Schwartz. "But we need to start 'undistorting' what we perceive to be a typical portion and begin to listen to our stomachs, not our eyes, to determine when to put the fork down."

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1Schwartz, J and Byrd-Bredbenner, C. Portion Distortion: Typical Portion Sizes Selected by Young Adults. J Am Diet Assoc. 2006; 106(9): 1412-1418.

2Guthrie, H. Selection and quantification of typical food portions by young adults. J Am Diet Assoc. 1984; 84(12): 1440-1444.


Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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