When I was studying nutrition, I remember learning the calories and serving sizes of hundreds of foods as part of a long list of things I would need to know as a dietitian. The food group I struggled with the most was fruits and vegetables. Most serving sizes for popular whole fruits such as apples and oranges are based on a per piece serving of a "medium" piece of fruit. I repeatedly asked myself, "How big is medium?"

In a society where bigger is seemingly better, our ability to control our portions is tested every day. A recent study explored the psychology of obesity, suggesting that our perception of portions is affected by what we perceive to be the societal norm and what our surroundings are telling us.

Have you ever gone to a restaurant with others and had "plate envy" because it looked to you like someone else got a larger portion? It doesn't matter that the other plate may have had a less calorie-dense entrée that permitted a larger portion. You still want what you think will meet your expectations. Most of us consider a "meal" the amount of food served to us on a plate, regardless of the amount of food or the size of the plate.

This study illustrates how conditioned we are to eat what's put in front of us, as long as it appears socially acceptable. Here are some examples of how as a society we have started to take the larger portion for granted!

• A bagel from your local bakery may be more than your anticipated single serving. In fact these days a bagel usually is 4 inches or more in diameter and averages around 300 calories, versus 150 calories for the single serving that should be around the size of a hockey puck.
• The difference between the basic burger offered at most fast food chains and larger, deluxe models is around 150 calories.
• Large sodas contain around 100 calories more than medium sodas, and "extra-super-large" sizes even more.

Back to my apples and oranges -- would you be surprised to learn that a small apple or orange is the size of a tennis ball?