So you are sitting across from your friend at a cafe, glaring longingly at their BLT with fries whilst you reluctantly dig into your salmon salad. To make matters worse they are a stick insect while it feels you just need to smell a potato before the weight piles on. Sound familiar? Researchers are now suggesting that our genetic make up could actually play a role in this unfair travesty.
These changes are down to genetic polymorphisms. Basically these are the natural variations in a gene that make you different from the person that was sitting next to you on the bus this morning. Genetic polymorphisms affect the genetic make up in many different ways but in this case it is specifically the changes to the number of genes. Termed copy number variations, these can result in one person having two copies of a gene whilst someone could have three or four (1). These variations can directly affect the amount of salivary amylase that someone produces.
The gene that makes amylase in the pancreas is AMY2 while the gene that produces salivary amylase is AMY1 (1). AMY1 in particular shows a much greater copy number variation, which suggests that AMY1 is critical to the starch metabolism differences between individuals. To put it simply, the more AMY1 genes that a person has the more salivary amylase they produce. The more salivary amylase someone produces, the more efficient they are at breaking down carbohydrates and the better blood glucose response they will have (2).
Even more interesting, cultures that traditionally relied primarily on starch for dietary energy appear to have higher copy numbers of the AMY1 gene and therefore produce more amylase, over populations who consumed a higher protein or fat diet (3). This has lead researchers to believe that evolution has played a role in increasing the number of AMY1 gene copies in select human populations, thereby improving the digestion of their traditional diet. Research is therefore heading in the direction that individuals who have a low copy number of the AMY1 gene may be more prone to insulin resistance, diabetes and even obesity (4). This could potentially shed some light on the BLT and French fry eating stick figure friend- that we all know and want to punch in the face.
1. Sudmant, P. H., Kitzman, J. O., Antonacci, F., Alkan, C., Malig, M., Tsalenko, A., . . . Eichler, E. E. (2010). Diversity of Human Copy Number Variation and Multicopy Genes. Science (New York, N.Y.), 330(6004), 641-646. doi: 10.1126/science.1197005
2. Mandel, A. L., & Breslin, P. A. S. (2012). High Endogenous Salivary Amylase Activity Is Associated with Improved Glycemic Homeostasis following Starch Ingestion in Adults. The Journal of Nutrition, 142(5), 853-858. doi: 10.3945/jn.111.156984
3. Perry, G. H., Dominy, N. J., Claw, K. G., Lee, A. S., Fiegler, H., Redon, R., . . . Stone, A. C. (2007). Diet and the evolution of human amylase gene copy number variation. Nature genetics, 39(10), 1256-1260. doi: 10.1038/ng2123
4. Santos, J. L., Saus, E., Smalley, S. V., Cataldo, L. R., Alberti, G., Parada, J., . . . Estivill, X. (2012). Copy number polymorphism of the salivary amylase gene: implications in human nutrition research. J Nutrigenet Nutrigenomics, 5(3), 117-131. doi: 10.1159/000339951