We make decisions about what and how much to eat every day… and if current obesity rates are any indication, we are far from experts! Historically, food intake and portion control were believed to be controlled by physiological and psychological factors. You eat and your body undergoes a series of physiological reactions that make you feel full, at which point you stop eating. These internal cues can be overridden by social or environmental factors though. For example, after the main course of your holiday meal you are stuffed and can’t eat another bite… then the freshly baked, homemade pie comes out and suddenly you have room for more! It’s your dessert stomach after all and your grandma would be insulted if you refused.
In general, we seem to be doing a poor job at regulating our food intakes, with many of us consuming too much; especially over the holiday season. With this in mind, it is important to have a complete understanding of the factors that regulate our caloric intake. Are there cognitive factors that affect our food intake? Research suggests that expectations about fullness and familiarity with foods can predict how many calories end up on our plate (1).
Brunstrom’s review (1), published in the Proceedings of the Nutrition Society, looks at the behavioural and cognitive determinants of meal size. In one study, they measured the expected satiety (how long you feel full for after a meal ends) of various foods. To do this they used pictures to compare test foods to a standard food; a food with a known amount of calories. Interestingly, they found that some foods were expected to be 5-6 times more filling than others. For example, when comparing pizza and pasta, participants thought a pasta meal providing 200 Calories would make them feel just as full as pizza providing 385 Calories (2), almost double! Why is this important? Well, it can predict how many calories end up on our plate.
We have to make decisions about portion sizes at every meal. If we consistently consume portion sizes that are too large it can lead to weight gain. Generally, we eat greater amounts of the foods we like (3). The palatability (taste) of many of the ‘Junk’ foods is often blamed for the obesity epidemic. But, are there other things that affect how much food we eat? These researchers report that smaller portion sizes were chosen when the food had a high expected satiation, defined as “the extent to which foods are expected to produce a feeling of fullness immediately after they have been eaten” (4). In short, we choose to eat less of foods that we think will make us feel full. This is important because we are actually not great at linking fullness to calories consumed (think back to the pizza and pasta example). They suggest that satiation is learned and that we come to anticipate it and adjust our portion sizes accordingly. Interestingly, they also found that if people were familiar with a food, they were more likely to expect it to make them feel full than if they were not familiar with the food (2).
What’s novel here is it suggests that we actually control how much we will eat before the meal starts when we decide on our portion. Here’s the proposed sequence of events:
- We have expectations about how full a food will make us feel and choose our portion size accordingly.
- The amount of food we put on our plate is going to determine how much we eat, regardless of fullness. This is supported by studies that show the amount of food on our plate predicts how much food we will eat (5). ‘Plate cleaning’ (eating everything put on our plate) was reported to occur in 91% of meals in one study. Indeed, when asked, people admit to planning to consume the entire portion of food on their plate at the beginning of the meal and continued to eat even if they were satiated (6).
What this means for you….. Realize that food choices should be conscious decisions, not mindless habits. Realize that, consciously or not, you are probably planning to eat everything you put on your plate and use your judgment. Realize that you are estimating how full foods will make you feel when you decide how much to put on your plate and inform yourself of the actual calories by reading the nutrition labels. Choose the lower energy density foods, as you know they will make you feel full without giving you a ton of calories.
(1) Brunstrom JM. The control of meal size in human subjects: a role for expected satiety, expected satiation and premeal planning. Proc Nutr Soc 2011; 70(2):155-161.
(2) Brunstrom JM, Shakeshaft NG, Scott-Samuel NE. Measuring ‘expected satiety’ in a range of common foods using a method of constant stimuli. Appetite 2008; 51(3):604-614.
(3) Cooke LJ, Wardle J. Age and gender differences in children’s food preferences. Br J Nutr 2005; 93(5):741-746.
(4) Brunstrom JM, Rogers PJ. How many calories are on our plate? Expected fullness, not liking, determines meal-size selection. Obesity (Silver Spring) 2009; 17(10):1884-1890.
(5) Rolls BJ, Roe LS, Meengs JS. Reductions in portion size and energy density of foods are additive and lead to sustained decreases in energy intake. Am J Clin Nutr 2006; 83(1):11-17.
(6) Fay SH, Ferriday D, Hinton EC, Shakeshaft NG, Rogers PJ, Brunstrom JM. What determines real-world meal size? Evidence for pre-meal planning. Appetite 2011; 56(2):284-289.