The Eyes Have It: Visual Feedback and Rates of Consumption

One of the topics that has really come to the forefront of late is the issue of rapid eating among those with disabilities. I recently administered a survey of eating disorders to a collection of adults with autism and other DD.  Surprisingly – well to me at least- I found a high level of rapid eating among the survey participants.  I have never previously considered eating too quickly as a nutritional risk factor but new research is emerging to demonstrate that it is a behavior of concern.

Rate of consumption is not an isolated factor, of course.  It is affected by numerous aspects of food including physical and textural qualities, portion size, and palatability.  Likewise, there are factors related to the individual that play a role including motivation, distraction, and level of hunger.

At one time the danger of rapid eating was primarily considered to be the possibility that insufficient chewing could lead to either an enhanced risk of choking and/or gastrointestinal distress.  Some research now suggests that individuals who eat quickly tend to consume more.  This is supported in several studies which correlate rapid eating to higher BMI:

Otsuka, R., et al. (2006). "Eating fast leads to obesity: Findings based on self-administered questionnaires among middle-aged Japanese men and women." Journal of Epidemiology 16(3): 117-124.

This emerging understanding has allowed a greater appreciation for how the rate of consumption affects satiation and the ways that insufficient feeling of fullness can lead to weight gain and even obesity.  For this very reason, I have developed an interest in factors that affect the rate of eating.  Lo and behold, a new article has emerged that addresses this issue straight on:

Wilkinson, L. L., et al. (2016). "Keeping Pace with Your Eating: Visual Feedback Affects Eating Rate in Humans." Plos One 11(2).

This paper plays with the hypothesis that cognitive processes relating to perceptual estimates of food play a role in rate of eating.  That is, the authors assert that when individuals are presented with a larger portion of a food, bite sizes are bigger and ingested more quickly.  To test this, the researchers developed a rather innovative experiment where participants were allowed to actually consume more than they could visualize:

 “This study explores the prospect that rate of eating might also be governed by a hitherto unexplored process that uses ongoing estimates of the volume of food remaining in a container to adjust food intake during a meal.”

The authors test this premise using a bowl with a hidden pump that allowed the contents to be altered independent of consumption.  In one scenario, for example, the participants saw and consumed either 300ml or 500ml of semi-solid food, in this case a tomato soup (savory) and a custard (sweet).  In the “incongruent” group the participants started with either 300ml or 500ml but actually consumed either 500 ml or 300 ml respectively.  Got it?

“At a constant eating rate, the volume in the bowl will reduce faster in the see 500ml/eat 300ml condition than in see 300ml/eat 500ml condition.  If eating rate is governed by a process that meters intake and corrects for faster- or slower-than-anticipated changes in perceived volume then we would expect to observe compensation for the mismatch.”

80 participants (50 female; 30 male) were utilized over 8 separate conditions.  I tried to think it through as to conditions: there were 300ml (meaning see and eat) or 500ml of both soup and custard (that’s 4 conditions), as well see 300ml/eat 500ml of soup and custard (2 more), and see 500ml/eat 300ml of soup and custard (2 more).  So eight conditions with ten individuals in each manifestation.

What were the outcomes?  There is actually quite a bit to report but from my perspective it is notable that those who ate 500ml portions all ate at a faster rate than those eating the 300ml portions.  However, the eating rates were not different when the amount seen was the same as the amount actually eaten.

This suggested to the researchers that eating rate is affected by visual feedback:

“Specifically, we found that eating rate was unaffected by the volume (300ml or 500ml) of food consumed in the two congruent conditions.  However, when we introduced a mismatch between meal size and perceived volume (the two incongruent conditions) then participants moderate their eating rate.  When offered a small portion in apparently larger volume participants ate at a slower rate than they did when offered an apparently small portion in a larger volume."

The authors expressed surprise that there was no relationship between amount being eaten (300ml vs. 500 ml) and amount seen (congruent vs. non-congruent) with fullness ratings.  Satiation was similar in both cases.

From my perspective, several mitigating factors emerge in this study.  First, the average age was 24.8 years and the average BMI was 23.2.  I would hypothesize the rates of consumption would be higher with participants who did not have a healthy BMI; their study skewed too lean to examine this.  Moreover, there are numerous logistical aspects to the study which caught my attention.  For example, the experiment was conducted with a dessert spoon; I hypothesize that if given a large soup spoon, consumption would be faster as well.  Further, semi-liquid substances are likely easier to consume than solid foods.  This, no doubt, affected outcomes.

Likewise, the authors were clever in the way the bowl was designed but there is no way to get around the fact that the experiment was done in a very clinical setting.  I anticipate that if the study had been undertaken in a more naturalized environment, rates of eating would have increased.

As always, I come back to the question of how to apply outcomes to adults with disabilities, particularly autism and those with intellectual disabilities.  How do orosensory cues get modified with cognitive limitations?  I don’t know, but this is an emerging topic that I will continue to track.