Eaters In The Dark: The Primacy of Cognitive Factors For Food Consumption And Satiety

To compare the importance of cognitive factors relative to physiological factors for estimating food consumption and satiety, we served 64 participants lunch in a “dark” restaurant where they ate a regular two-course meal in complete darkness. Half the participants unknowingly received considerably larger portion sizes which subsequently led to higher food intake. Despite this difference, participants’ appetite for dessert and their subjective hunger after the meal was largely unaffected by the amount of food they had consumed in the dark. In comparison, 32 participants in a control group who ate the same meal in the light consumed comparatively less food from the large portion and still compensated for the larger portion size by eating less dessert afterwards. Together, these results indicate that internal physiological cues do not provide accurate feedback and that visual cues are the main source of information for estimating food intake and satiety. Nikola Tesla, the eccentric inventor, worried about eating anything which he could not visually judge the size of before he consumed it (Hunt & Draper, 1964). As Tesla was also concerned about his weight, his peculiar behavior could have been connected to a fear of overeating when lacking appropriate visual input. How important are visual cues for controlling our food consumption and when to stop eating once we start? Physiological research has identified a number of postingestive satiety processes involving the integration of numerous internal signals that trigger the inhibition of our appetite (Schwartz et al., 2000; Barsh, Farooqui, & Rahilly, 2000). But this need to inhibit appetitive behavior internally would rarely come up in an environment where food resources are scarce, as the possible amount of food available to consume is externally constrained. Thus our proprioceptive signaling systems that evolved for meal termination in challenging Pleistocene environments might be less sophisticated than the signals that arose to first motivate us to eat. As perhaps felt by Tesla, this poses a problem in a world where large amounts of high-calorie foods are ubiquitous, as in our modern affluent societies; and it might even be a reason for the growing rate of overweight in numerous countries, a development sometimes referred to as the ‘obesity epidemic’ (Bolles, 1965; Jeffery et al. 2007; Blundell et al, 2005). To determine how much food they have consumed and when to stop eating, people often rely instead on external cues in their environment (Fedoroff, Polivy, & Herman, 1997; Schachter, 1968). The simplest case is that people typically stop eating once they empty their plate, which can lead to increased consumption with larger dish and portion sizes (Wansink, Painter, & North, 2006; Diliberti, Bordi, Conklin, Roe, & Rolls, 2004; Levitsky & Youn, 2004; Fisher, Rolls, Birch, 2003; Rolls, Roe, Kral, Meengs, Wall, 2004). When eating in a group, people also adjust their consumption to how others at the table eat, presumably because this sets an implicit consumption norm (Herman, Roth, & Polivy, 2003). To the extent that food intake is controlled by cognitive processes that rely on external cues, subjective feelings of satiety may depend little on the actual amount of food in the stomachs. In line with this, Rolls, Morris, and Roe (2002) found that larger portion sizes led to more consumption among participants but did not affect their subsequent ratings of hunger and fullness. Likewise, Wansink, Painter, and North (2006) showed that manipulating visual cues of how much is eaten influences further intake, suggesting that “people use their eyes to count calories and not their stomachs” (p.98). They served participants soup in a bowl that secretly re-filled through a hidden tube in the bottom. Participants who ate from these “bottomless” bowls on average consumed 73% more calories than a control group eating from regular bowls, yet they did not report having consumed more, nor were they more sated. Longitudinal studies show that such overconsumption of food is often not