Portion Control

Portion-Size Trends

Since the 1970s, portion sizes of commercially available foods and beverages have increased significantly both inside and outside the home. Portion sizes of many marketplace foods and beverages often greatly exceed serving size standards specified by the U.S. Department of Agriculture. The largest excess can be found for energy-dense foods such as cookies, muffins, salty snacks, and fast food items. At the same time, value size pricing, which involves structuring product prices such that the per-unit cost is lowest for larger portions, encourages the purchase and consumption of larger size portions. With more consumers regularly eating out, the trend to purchase large quantities of foods for only a small price increase has become especially problematic.

Effects on Energy Intake

Studies conducted in the laboratory and the free-living environment have consistently shown that increasing the portion size of foods and beverages that are served at a meal significantly increases energy intake in adults. Laboratory studies indicate that portion size can also affect energy intake in children as young as 2 years of age, although the effects on intake have not been as consistent as those seen in adults.

Portion size affects energy intake across different types of foods that come in either discrete (e.g., sandwiches) or amorphous (e.g., pasta) shapes served both as snacks and meals. Large portions have the most significant impact on energy intake when foods are energy dense and therefore pack many calories into each bite. The main components of food that influence energy density (calories per gram) are its fat and water content. Where as fat increases a food's energy density, water lowers it. Studies in adults and children have shown that large portions of foods high in energy density can significantly increase energy intake. On the other hand, large portions of foods that are low in energy density, such as fruits, vegetables, or broth-based soups, when eaten either before or during a meal can moderate energy intake.

Laboratory studies have also shown that portion size affects energy intake beyond a single meal. For example, increasing portions of all available foods and beverages over 11 days resulted in a sustained increase in energy intake over the entire period. The increased energy intake associated with increased portion sizes did not result in energy compensation at subsequent meals. Similarly, when the portion sizes of entrées and midafternoon snacks were increased over 24 hours, 5-year-old children and their mothers consumed significantly more energy. Therefore, the availability of large portions of foods and beverages over multiple days is associated with a sustained increase in daily energy intake, supporting the possibility that portion size could play a role in the development of obesity.

...