Is There More to Taste Than Simple Preference?

 

It seems like everyone these days can agree on what tastes good and what tastes bad –for example the cake on the left looks delicious, but the baby mouse donut on the right - although most of us have never tasted it before - doesn’t seem to trigger our appetite, no matter how hungry we may be. 

So what exactly drives our taste perception and preferences?

Many of us think taste is independent of our other senses (Drewnowski 1997), but try eating a jelly bean while holding your nose closed with your other hand (Small 2008)  – you can’t seem to taste the flavor now, can you? In fact, smell – along with other chemical irritations - plays a large component in our judgment of taste. Most of us might have learned this in grade school, but here’s something new: Beauchamp, Gary & Mennella recently published a paper on their discovery that in addition to being innate, taste can also be learned both pre- and post- natally. The 5 taste preferences: sweet, sour, salty, bitter, umami, and savory are developed at different stages in life – in fact, an infant innately prefers sweet, umami, and salty flavors over the others due to the nutritional needs these tastes provide in order for the infant to survive. Glucose is essential for anabolic and catabolic processes, explaining the innate tendency to favor sweet foods, while proteins are essential in muscle building and enzyme functioning, justifyingthe umami preference. Salt, too, is necessary to help buffer membranes, and help drive neuronal signals. In contrast, sour and bitter flavors are disfavored early on because these substances are 1) not necessary for proper bodily functioning and 2) are most likely harmful to the individual. In fact, our “gag” response to such appalling flavors is a reflex, informing us to avoid potentially toxic substances that may lead to sickness or even death. Evolution has affected our taste preferences before we are even able to recognize it!

Despite this evolutionary basis, these inherent tendencies can be changed both pre-and post-natally (Beauchamp et al 2009). These choices can result in drastic life-long food preferences and in turn, can potentially determine the long-term health of the individual. For example: children who were fed milk daily and kept drinking milk until middle-age will retain lactase, the enzyme that breaks down milk lactose (Holden, Mace 2003; Simoons 2007); however, those individuals who stop drinking milk in their infancy and suddenly drink milk in their teens may develop lactose intolerance (Food Reactions). Why does this occur? Humans only depend on their mother’s milk in their infancy – once infants are no longer breast-fed they naturally loose lactase since it is no longer needed - they no longer “require” milk for development. This is the evolutionary perspective, yet these days humans continue to consume milk past their infancy, but from cows rather than from their mothers. Because this development is, in a sense "unnatural", we retain our enzyme if we continuously drink milk, but if we stop drinking milk for some time, we lose it.

Here is another example with greater consequences: many individuals who are overweight/obese and who grow up consuming excessive sweets are more prone to develop type II diabetes in which their bodies produce insulin, but cannot respond to it (Lieberman 2003). So why exactly are we so attracted to sweets and fats if doing so increases the odds of chronic disease and obesity? The evolutionary reason is that these substances contain a high concentration of energy (carbs, calories, glucose), keeping us full for a longer period of time. Back in the day, humans had to scavenge for food - a process that took much time and energy, and if food was not found in time, the individual would starve and die. Thus, foods with high energy were favored over those with less energy, such as fruits and veggies since they provided greater energy over a longer period of time. Over the centuries, the increased efficiency and prevalence of domesticated livestock and fast-food choices have led to both over-consumption and a more sedentary lifestyle, contributing to the prevalence of obesity and type II diabetes seen today.

As the occurrence of these chronic illnesses increases, it becomes ever more important to establish good eating habits, which is where Beauchamp et al’s paper comes into play: these researchers discovered that an infant’s taste preference can be altered depending on what the pregnant mother’s diet. Thus, in order to for the infant to “defy evolutionary preferences” and favor bitter flavors such as vegetables over sweet, unhealthy ones such as cake and candy bars, a pregnant woman should simply eat more fruits and vegetables during her pregnancy in order for the infant to become familiar with and “learn” to prefer these flavors over the innate ones. This study suggests a simple mechanism to promote healthy foods at an earlier age in face of the increased convenience and attraction to unhealthy foods due to marketing.

- Effie 

Sources:

Beauchamp, Gary K; Mennella, Julie A. Early Flavor Learning.2009. Journal of Pediatric Gastroenterology & Nutrition. Volume 48: S25-S30 (doi: 10.1097/MPG.0b013e31819774a5) link: http://journals.lww.com/jpgn/Fulltext/2009/03001/Early_Flavor_Learning_and_Its_Impact_on_Later.5.aspx.

Drewnowski A.Taste preferences and food intake. 1997. Annu Rev Nutr. Vol 17: 237-53.

Food Intolerance – A Comprehensive Guide to Lactose Intolerance: http://www.foodreactions.org/intolerance/lactose/.

Holden, C., Mace, R. Phylogenetic Analysis of the Evolution of Lactose Digestion in Adults.2009. Human Biology. Vol 81(5-6):597-619. doi: http://dx.doi.org/10.3378/027.081.0609.

Lieberman, S. Dietary, evolutionary, and modernizing influences on the prevalence of type 2 diabetes. 2003. Annual Review of Nutrition. Vol. 23: 345-377. doi: 10.1146/annurev.nutr.23.011702.073212.

Simoons, F. Primary adult lactose intolerance and the milking habit: A problem in biologic and cultural interrelations . 2007. Digestive Diseases and Sciences. Vol 15, (8): 695-710, doi: 10.1007/BF02235991.

Small, D. How does the way food looks or its smell influence taste? 2008 Vol 4. (http://www.scientificamerican.com/article.cfm?id=experts-how-does-sight-smell-affect-taste.