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Food, Health, and Eco-news
Portion Control for Weight Control: Size Perceptions Called Key
Study finds value in exploiting people’s pliable perceptions of size 01/04/2007 by Craig Weatherby
It will come as a surprise to few that the daily food-energy intake of the average American man rose by 168 calories over the past 30 years, or that the average American woman's intake rose by 335 calories a day during the same period.

These increases result in part from foods becoming ever cheaper and more ubiquitous and from restaurants serving bigger portions.

And stress-related eating may also have played a role, given the large numbers of layoffs in the manufacturing sector and decreased job security during this period.

Perceptions affect consumption
Research results indicate that people will eat what's presented to them, past the point of satiety.

So it seems obvious that one way to cut calorie intake is to reduce portion size. But people are poor judges of portion size.

One effective way to cut portion size
and your own perception of a serving's substantialityis to use smaller plates and

Eye of the Beholder
The Ebbinghaus-Titchener size-contrast illusion shows how people's perceptions of sizes depend on context.

Both white circles are the same size, but appear different because of their surroundings.

In 2002, Cornell University researchers tested this hypothesis in an ironically ideal context: 85 nutrition experts who were attending an ice cream social to celebrate the success of a colleague.

You'd think these folks would be good at judging portion sizes, but you'd be wrong.

At random, the attendees were given smaller (17 oz) or larger (34 oz) bowls and smaller (2 oz) or larger (3 oz) ice cream scoops.

The nutrition experts given a larger bowl served themselves 31 percent more without being aware of it. And their servings increased by 14.5 percent when they were given a larger serving spoon.

Despite the measured differences in portion sizes, the nutrition experts all believed that they'd consumed about a cup (8 ounces) of ice cream, and were equally satisfied.

As the investigators concluded, "People could try using the size of their bowls and possibly serving spoons to help them better control how much they consume. Those interested in losing weight should use smaller bowls and spoons …”

Soup study confirms perception problem
Three years later, the same Cornell team recruited 54 people to participate in a similar study involving soup.

The trick this time was that some of the volunteers ate their soup from bowls that refilled slowly and imperceptibly as their contents were consumed (All of the volunteers' bowls were set into a table, with the filling mechanism concealed).

The researchers recorded the volunteers' soup intake, their own estimates of their soup intake, and their perceptions of satiety.

The participants who ate, unknowingly, from self-refilling bowls ate 73 percent more soup than those eating from normal soup bowls, yet they did not believe they had consumed more soup, nor did they feel more satiated (These results were unaffected by the volunteer's body-mass indices).

The Cornell team came to the obvious conclusions: "It seems that people use their eyes to count calories and not their stomachs. The importance of having salient, accurate visual cues can play an important role in the prevention of unintentional overeating.”

Their findings dovetail with the results of experiments showing that entrée-portion control enhances weight control in women (Hannum SM et al 2004), that young adults will eat as much as is served to them (Levitsky DA ET AL 2004), and that people typically underestimate the size of portions they've just consumed (Harnack L et al 2004).

  • Wansink B, van Ittersum K, Painter JE. Ice cream illusions: bowls, spoons, and self-served portion sizes. Am J Prev Med. 2006 Sep;31(3):240-3.
  • Wansink B, Painter JE, North J. Bottomless bowls: why visual cues of portion size may influence intake. Obes Res. 2005 Jan;13(1):93-100.
  • Hannum SM, Carson L, Evans EM, et al (2004) Use of portion-controlled entrees enhances weight loss in women Obes Res. 12,538-546.
  • Harnack L, Steffen L, Arnett DK, Gao S, Luepker RV. Accuracy of estimation of large food portions. J Am Diet Assoc. 2004 May;104(5):804-6.
  • Levitsky DA, Youn T. The more food young adults are served, the more they overeat. J Nutr. 2004 Oct;134(10):2546-9.