Grand proportions: Does portion size lead to obesity?

In the movie "Supersize Me," Morgan Spurlock gained 30 pounds in a month by eating super-sized portions at McDonald's for every meal. Are we doing something similar to our children?

Obesity is increasing in people of all ages, including children as young as 4 years old. The increase has affected both genders and all ethnic groups examined, although not equally.

We should ask ourselves two questions: What went wrong? and What can we do about it?

Decreased activity (energy expenditure) and increased energy intake are the two obvious explanations for why obesity is increasing. On the increased intake side of the equation, portion size (and by implication the amount of food consumed) often is cited as part of the problem.

Portion size is the amount of food that is offered, while portion consumed is the amount of a food that is actually eaten. Put another way, portion size is how much broccoli a mother puts on her child's plate or how many french fries come with a child's Happy Meal, while portion consumed is how much of the broccoli or how many of the french fries the child actually eats.

While portion size is increasing, evidence does not support this factor as the sole cause for the increase in obesity.

There is no question that out of home, marketplace portion sizes have increased in the United States over the past decades. To be convinced of this, one need only take note of the increased size of soft drink containers (from 6 ounces in the 1960s to 12 to 16 ounces, even 64 ounces now) or look at the advertisements for "super-size french fries." Marketplace food portion size now frequently far exceeds the federally recommended serving size. The question of whether increased portion size actually leads to increased intake is less clear.

There is a long-held belief, supported by research dating back to the 1920s, that children will self-regulate their energy intakes when given appropriate and healthy choices. More recent research has shown that infants and toddlers eat predominantly according to their hunger. However, this changes with increasing age, so that by age 5, children eat not only to satisfy their hunger (internal cues) but also in response to their environment (external cues). These environmental cues can include TV advertisements, boredom and activities that keep children and adolescents indoors. Another external cue could be large portion size. Although possibly coincidental, it is interesting that the onset of response to external cues corresponds to the onset of recorded increase in overweight.

When children 5 years and older and adults are offered larger portion sizes, they eat more. The bigger the portion size, the more of that food is consumed. One might jump to the conclusion that this would lead to overeating and thus overweight, but this is equally true for overweight, appropriate weight and even under-weight people.

Other explanations for the increase in calories consumed are more eating occasions (more frequent meals and snacks), increased variety of foods eaten (not having just a peanut butter and jelly sandwich for lunch but also macaroni salad, fruit cocktail and dessert) and increased caloric density of the foods eaten.

As an explanation for increased obesity, what really matters is how much is actually eaten, that is, the portion consumed, not how much is offered. So, has the portion consumed increased?

Large national surveys show little evidence that portion consumed has increased over the past decades. For children ages 6 to 11 years, comparing the Continuing Food Survey Intakes by Individuals data from 1989-'91 with data from 1994-'96, the reported portion consumed increased for only two of 107 foods tallied, while the portions of pizza, chicken and margarine were reported to have decreased. The reported portion consumed for children ages 12 to 18 months also declined.

So, a partial answer to the first question of what went wrong is that the increased prevalence of overweight in the pediatric population is multifactorial and complex. The jury is still out, but the evidence does not support portions as the sole cause for the increase in obesity.

The analysis of the evidence does offer an untested but potential answer to the second question: What can we do about obesity and overweight?

Since portion size affects how much is eaten, offering more appropriate portion sizes should result in curtailed energy consumption. Doing this may help us return to the days when children self-regulated their energy intake. It may not be the portion sizes alone (e.g., a large soft drink or a super-sized french fry) that are to blame. Rather, given these along with TV time, boredom, the entire amount of food consumed plus the absence of physical activity lead to extra unused calories. In this light, portion size does makes a difference!