Consuming the appropriate portion size of the foods we eat is a vital part of eating healthy. However, it has become one of the things with which we have the greatest amount of difficulty. Part of this is likely due to the way portion sizes have changed over the years. A hamburger 20 years ago was much smaller than a typical fast food hamburger we consume now. This change in portion sizes over time has distorted our concept of correct portion sizes.
One nutrition study used a computerized tool to determine how accurately adolescents estimate portion sizes. For this study, adolescents between the ages 11-17 years were asked to estimate portion sizes in two ways. In a short-term recall test, the children served themselves their usual amounts of 10 foods and later in the day were asked to estimate the amount they ate. In a real-time perception test, the children were asked to estimate pre-weighed portions. On average, the children in the study underestimated their self-served portions by 8% with substantial underestimations for breakfast cereals and French fries among others. The results of the real-time perception test were even worse with children underestimating portion sizes by 15% on average. Substantial underestimations in this test were found in 14 of the 20 portions.
These results make it pretty clear that not only us adults underestimate portion sizes. By underestimating portion sizes, we put ourselves into situations where we are eating more that we realize. The size of food items presented to us at stores and restaurants is typically much more than a single serving. For example, the 12 oz. steak we might be intent on grilling over the weekend is not one serving; it is actually 4 servings of meat. By assuming that one 12 oz. steak is one serving size, we find ourselves eating a lot more than planned throughout the course of a day. Learning how to estimate correct portion sizes is an important part of designing a healthy eating plan. In addition to actually weighing or measuring your food as you prepare it, you can visualize appropriate portion sizes. For example: