Does A Serving Size Affect The Way You Eat?

The focus of many fast food menus is on larger burgers, drinks and fries. At the same time, weight-loss programs emphasize decreasing the amount of total food eaten as a way to lose weight. The connection between what is served and what is consumed is receiving more attention.

Serving versus Portion

The terms "portion size" and "serving size" are often used interchangeably, although the National Center for Chronic Disease Prevention and Health Promotion defines them differently. Serving size is a standard unit for measuring food --- a cup or an ounce. Portion size, on the other hand, is the amount of a particular food item offered or served to an individual in one meal or snack. A large bagel, for example, may well be the equivalent of two servings in terms of calories, yet is often served whole and consumed as a single portion.

Portion Size and Food Intake

Research has shown that the more food people are offered, the more they eat. Barbara J. Rolls, reporting in "Portion Sizes and the Obesity Epidemic," found that a portion of food containing more than one serving will still be consumed, even though there is more food than usual. In many cases, people will not even notice the portions are larger. Rolls' team looked at gradually increasing amounts of potato chips in bags that otherwise looked exactly the same; study participants ate more food from the larger bags. Even though the participants had consumed a larger snack than usual, they did not adjust their food intake at dinner to compensate for the increased calories.

Research on Food Intake

A classic research study of 1977 used trick soup bowls that were gradually refilled from a secret reservoir below the table. People who were obese continued to eat more even after the trick was explained, while those of normal weight adjusted their intake on learning of the refill process. In a study published in 2005 in the "Journal of the American Medical Association," a team of researchers found that offering snacks in large bowls led to an increased food intake by study participants, while smaller serving bowls had the reverse effect. The Centers for Disease Control and Prevention reported that all research studies have shown the same results for both genders as adults, but noted several studies showed that children under 2.5 years adjusted their food intake despite portion size. As children grew older, if they had been consistently offered larger amounts of food, they ate more.

The Importance of Portion Size

Portion sizes, as indicated by current research, are the key to food intake. Serving size, being a standard measure, does not affect how people eat, but larger portion sizes do seem to lead to higher food intake.