How Portion Size and Paying Attention Affect Your Eating BehaviorIt has been suggested that we are often unaware of external factors that influence eating behavior (Wansink, 2006; Vartaninan et al., 2008).  There is a substantial body of research that shows external factors have a robust influence on eating behavior (Epstein et al., 2009; Remick et al., 2009; Rozin et al., 2003). 

These external factors include things such as portion size, labeling, variety of food we eat, and how much attention we pay when we’re eating (or whether we’re distracted by socializing, for instance). Even the plate size can affect how we eat.

Now, some researchers have suggested that external factors may play a larger role in eating behavior than internal factors, such as hunger, satiety, flavor, macro-nutrient content, and so on (Wansink et al., 2007; Levitsky, 2005; Wansink, et al., 2005). 

What’s behind these external or environmental factors and their role in how we eat?

External (Environmental) Factors

At one time it was widely assumed people ate when they were hungry and stopped when they were full, as behavior responded to physiological signals.  More recently, a variety of factors have been shown to influence food intake, e.g. cultural factors, influences of the food industry, environmental factors and more (Vartanian et al., 2008; Rozin, 1996; Wansink et al., 2009).  Of those factors, external factors appear to be some of the strongest influences on eating behavior.

There is a substantial amount of evidence showing that external factors can influence people’s eating behavior (Remick et al., 2009; Herman et al., 2005). Some of these external factors include portion size, socializing, variety, labeling and plate shape (Wansink, 2004).  These factors often work together or with other influences to shape food intake.  Primarily, external factors affect our eating behaviors by interfering with consumption norms or they disrupt our ability to monitor how much we have eaten (Wansink et al., 2009). 

For many people deciding how much to eat or drink is a burden, so instead of spending to much time thinking about it, they instead rely on consumption norms to help when choosing how much to eat.   Consumption may be influenced by how much one typically buys or consumes. 

Consumption may also be influenced by other cues or norms in the environment.  Package size, variety, utensil size, or presence of others my suggest a consumption norm that affects how much one drinks or eats.  These norms suggest an optimal quantity that we should eat or drink (Wansink et al., 2009; Wansink et al., 2004).

External factors have been shown to bias one’s estimate of how much they have eaten.  Even when people were given information that larger package sizes often cause individuals to underestimate consumption by 20%, many of these people in field and lab studies incorrectly said they were not affected by package size (Wansink, 1996). 

A major determinant of how much one eats in a distracting environment is whether or not the person is trying to monitor their intake.  Eating is a multidimensional process that is sometimes difficult to monitor.  This can lead to individuals focusing more on food choice than food volume. 

For example, people eating at an Italian restaurant correctly believed that if they ate butter with each slice of their bread they would consume fewer fat calories per slice than they would if they dipped their bread in olive oil. This became problematic as they compensated for this reduction in fat calories by eating 23% more bread over the course of the meal (Wansink & Linder, 2003).     

References available upon request.

Woman eating a hot dog image available from Shutterstock.