Nutritional Pearls: Personal Portion Sizes

Robert is a 30-year-old overweight man struggling to lose weight. At his most recent check-up, he brings up his difficulty determining appropriate serving sizes for many of the foods that he eats.

How would you advise your patient?
(Answer and discussion on next page)

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Answer: A patients weight can influence their interpretation of a “normal” serving size.

I've spoken and written extensively about portion size and the importance of portion control in weight management. This is partly in response to what is often termed "the super-sizing of America," but it's not just restaurants where portion sizes have blown up in the last several decades. Even portions in cookbooks have been shown to have increased over time. That means that for a lot of people, they have no idea what an actual portion size should be—because they've probably never seen one.

The Research

A team of researchers in the United Kingdom recently published a study that sought to get an idea of what people thought of as a "normal" portion size. In doing this, they noted that people often have an idea of what is normal for them and often see what is normal for others differently. The authors theorized that those who are what we consider to be clinically normal body weight would have smaller personal and social definitions of what is a "normal" portion size than those who are considered to be clinically obese.
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To investigate this idea, they recruited 30 men and women of clinically normal weight (body mass index between 20 and 25) as well as 30 men and women who were clinically obese (body mass index between 30 and 35). On 2 separate occasions a week apart, each participant came to the lab and viewed 17 portion sizes of a dozen common foods on a computer screen. On the first occasion, for each image the participant was asked, "At a typical eating occasion when you would eat this food, would you normally have less or more than the amount shown?” Each image was of the same size on the computer screen and showed different amounts of the food on a standard size dinner plate or bowl complete with place setting and drinking glass for size comparison.

The second visit was the same as the first, except that the participant was asked, "At a typical eating occasion when this food would be eaten, most other people would normally have less or more than the amount shown?"

At the beginning of both sessions the subjects responded to questionnaires that measured their hunger and desire to eat. At the end of the second session they were asked how much they liked each specific food.

The Results

The authors correlated each participant’s portion size indicators, both for themselves and for others, with their body mass index, gender, hunger level at the time of testing, and age. They found that, as they had expected, those who were obese tended to have larger personal normal amounts than those who were of normal weight, and their personal norms were also larger than what they believed others would normally eat. Similarly, men's personal portion sizes tended to be larger than those of women, regardless of the participant's weight.

What was especially striking about their results is that the personal normal sizes for all of the participants was larger than what is considered a "normal" serving size by UK standards.

What’s The “Take Home”?

While this data suggests that those who define serving sizes may need to recalibrate according to what people feel is a "real" portion size, this also highlights the need to assess your personal portion sizes if you are working on your weight.

Reference:
Lewis HB, Forwood SE, Ahern AL, et al. Personal and social norms for food portion sizes in lean and obese adults. Int J Obesity. 2015;39:1319-1324.