Since obesity has been rising for decades and causes so much loss of life and disability my next few blogs will focus on issues that can lead to overeating. I will talk about how hormones in our gut tell our brain when we are full, how food choice is affected by hunger and our emotions, the satiety of different foods and so on. This blog will focus on our increasing portion sizes and how our eyes often mislead us on how much we eat.
For the past few decades portion sizes have been steadily increasing. Some examples of how our portion sizes increased since the 1950’s are: the average hamburger sandwich was 3.9 oz, now it is 12 oz, French fries were 2.4 oz then now they are 6.7 oz, soda was 7oz, today it is 42 oz (that’s a 440 calorie increase!). These small changes can lead to consuming a few hundred extra calories a day which over a year can result in putting on a substantial amount of weight.
Studies showing how portion size regulates intake
In one study subjects came into the lab two consecutive days in each of three weeks, and ate breakfast lunch and dinner at scheduled times in a cubicle (1). After the meals subjects were given snacks to eat away from the lab at midmorning, midafternoon and in the evening (1). Each week, the portion sizes were increased by 100%, 150% or 200% compared to the baseline amount (1). For both men and women, as portion sizes increased so did energy intake (1).
When the portion size was increased by 50% above baseline, energy intakes increased by 16% (1). When the portion size was increased by 100% above baseline, energy intakes increased by 26% (1). Even though their intake increased on those days, there was no decrease in caloric intake on the following day to compensate for the increased food intake from the previous day (1). When portion sizes were increased subjects increased their intake of energy dense snacks like potato chips but their intake of fruits and vegetables stayed the same (1). Subjects reported they knew the portion sizes increased and that they consumed more food but few believed that the portion size affected their intake (1).
An interesting study highlighted just how influential portion size can be in the amount of food consumed. Movie goers were given either a free medium or large popcorn. The study used fresh and stale (14 days old) popcorn (2). For fresh popcorn, subjects ate 45.3% more popcorn from the large versus the medium container (2). For stale popcorn, subjects ate 33.6% more popcorn from the large versus medium container despite 73 of 86 subjects rating the popcorn as, “stale,” “soggy,” or “terrible” (2). This study found that in a distracting movie environment portion size had a greater influence than even taste on amount of popcorn consumed.
Another study measured the effect of portion size on food intake in participants served differing amounts of lunch 1 day a week for four weeks (3). Subjects in both the men and women group consumed 27% (79 gram) more food and energy (536 kJ) when they were given the largest portion compared to the smallest portion (3).
Lastly, a study measured the intake of soup in individuals given a normal bowl or a bowl that was refilled as subjects ate (4). The self refilling bowl was slowly refilled from a machine as the subjects were eating the soup (4). In the normal bowl group, when the soup got to 25% of its original amount, servers came and refilled the bowls (4).
People from the self refilling bowl ate more soup than the subjects eating from a normal bowl (14.7 versus 8.5 ounces) (4). This resulted in a 73% increase in the amount of soup consumed and an increase of 113 calories (4). Those in the self refilling bowl group did not believe that they consumed more soup than the normal bowl group nor did they report being any more full than the normal bowl group (4). The normal bowl group underestimated their caloric intake by 32.3 calories while the self refilling bowl group underestimated by 140.5 calories (4).
How good are we at estimating portion sizes?
So, how good are we at estimating portion sizes? Apparently, not very good. A study involving 49 subjects took place at a conference hall where participants were served various foods and afterward interviewed and asked to estimate the portion sizes using 3D plastic containers as estimation guides (5). Underreporting of portion size was seen for the hamburger and French fries served but not the ice cream (5). When asked to estimate the total calories of the meal, subjects estimated 728 calories while the meal was actually 998 calories (5).
It seems that children are no better than adults at estimating portion sizes (6). Weeks before the study children were exposed to an age appropriate portion and a larger portion to show the differences. When children were served an entrée which was doubled the normal portion size their intake of the entrée increased by 25% while their total energy (from the whole lunch meal) intake increased by 15% (6). When children were later allowed to serve themselves, they picked amounts closer to the appropriate portions sizes and not the larger portion sizes, consuming 25% less of the entrée compared to when served a large portion size (6). Most children were unaware of the different portion sizes they were eating (6).
The effect of high reward foods
Okay so what about those 100 calorie snack packs? Surely that can help cut back on your snacking. Ever hear the Lays chips slogan “betcha can’t eat just one. “Turns out there is some truth to that. Against common sense opinion, sampling of a high reward food (chocolate, soda) may increase our desire to attain additional high reward food. A study showed that subjects who consumed Pepsi not only increased their consumption of other high reward foods (chocolate) but to rewards in general (a massage) (6).
The authors believe that cues high in incentive value result in activation of a general motivational state (6). I can attest that this is true for me when eating sugary foods. I have a weakness for these foods so I generally avoid them but if there is candy at work or cake at home I will consume all of it within a few days. I know it’s bad for me and there isn’t much upside to eating it but I can’t help it. Once I start I don’t stop until I get a stomach ache. Never do I think “well that’s enough of that,” if there is more left to eat. These types of foods offer no relief such as getting full or being satisfied.
Another study showed when given snacks (apple pie, potato chips, chocolate) of varying sizes to subjects, the small portions satisfied hunger and cravings similar to seen from large portions (7). The large portions were 5-10X as big as the small portions (7). This led to a decreased caloric intake (7). The study showed that if offered a larger portion of a snack food we will eat more even though our cravings may already be satisfied.
We are not good visual estimators of portion sizes. To help this, we should buy smaller bowls and cups to decrease the amount we can fit in them. We should measure portion sizes by putting them in a measuring cup when possible. We should get rid of the idea that we must finish the plate regardless of size. If you know you have a weakness for certain bad foods do not buy them. If you don’t have it in your house you can’t eat it. Once you eat one high reward food you may desire more of these kinds of foods so avoidance may be best.
Avoid buffets. Multiple studies have shown that we consume a lot more than we think at buffets. It is hard to keep track of how much you are eating when you have unlimited food. Restaurant portions sizes are huge so share them with a friend or take some home to eat at another time. As portion sizes increase everywhere our brain starts to associate these portions as “normal,” even if they are big. When portions are enlarged we will eat more, even when we don’t particularly care for a food, such as the case with the stale popcorn, so always choose the smaller portions since this will likely satisfy you as much as the larger portions with far less calories. Make a conscious effort to evaluate the portion size of all the foods you eat.
Although there are tons of factors contributing to obesity, portion size is likely a large contributor, so having knowledge in this area is a huge step in the right direction in accurately controlling your intake of food!
1. Rolls, B. J., Roe, L. S., & Meengs, J. S. (2006). Larger portion sizes lead to a sustained increase in energy intake over 2 days. Journal of the American Dietetic Association, 106(4), 543-549.
2. Wansink, B., & Kim, J. (2005). Bad popcorn in big buckets: portion size can influence intake as much as taste. Journal of nutrition education and behavior, 37(5), 242-245.
3. Rolls, B. J., Morris, E. L., & Roe, L. S. (2002). Portion size of food affects energy intake in normal-weight and overweight men and women. The American journal of clinical nutrition, 76(6), 1207-1213.
4. Wansink, B., Painter, J. E., & North, J. (2005). Bottomless Bowls: Why Visual Cues of Portion Size May Influence Intake**. Obesity Research, 13(1), 93-100.
5. Harnack, L., Steffen, L., Arnett, D. K., Gao, S., & Luepker, R. V. (2004). Accuracy of estimation of large food portions. Journal of the American Dietetic Association, 104(5), 804-806.
6. Fisher, J. O., Rolls, B. J., & Birch, L. L. (2003). Children’s bite size and intake of an entree are greater with large portions than with age-appropriate or self-selected portions. The American journal of clinical nutrition, 77(5), 1164-1170.
7. Van Kleef, E., Shimizu, M., & Wansink, B. (2013). Just a bite: Considerably smaller snack portions satisfy delayed hunger and craving. Food Quality and Preference, 27(1), 96-100.