I had a look at the scientific literature and found that they think that a high carb diet may have exerted evolutionary pressure for more copies of the amy1 gene:
http://www.ncbi.nlm.nih.gov/pubmed/17828263Nat Genet. 2007 Oct;39(10):1256-60. Epub 2007 Sep 9.
Diet and the evolution of human amylase gene copy number variation.
Perry GH1, Dominy NJ, Claw KG, Lee AS, Fiegler H, Redon R, Werner J, Villanea FA, Mountain JL, Misra R, Carter NP, Lee C, Stone AC.
Author information
Abstract
Starch consumption is a prominent characteristic of agricultural societies and hunter-gatherers in arid environments. In contrast, rainforest and circum-arctic hunter-gatherers and some pastoralists consume much less starch. This behavioral variation raises the possibility that different selective pressures have acted on amylase, the enzyme responsible for starch hydrolysis. We found that copy number of the salivary amylase gene (AMY1) is correlated positively with salivary amylase protein level and that individuals from populations with high-starch diets have, on average, more AMY1 copies than those with traditionally low-starch diets. Comparisons with other loci in a subset of these populations suggest that the extent of AMY1 copy number differentiation is highly unusual. This example of positive selection on a copy number-variable gene is, to our knowledge, one of the first discovered in the human genome. Higher AMY1 copy numbers and protein levels probably improve the digestion of starchy foods and may buffer against the fitness-reducing effects of intestinal disease.
and that people with more copies of the gene appear to handle carbs better:
http://www.ncbi.nlm.nih.gov/pubmed/22492122J Nutr. 2012 May;142(5):853-8. doi: 10.3945/jn.111.156984. Epub 2012 Apr 4.
High endogenous salivary amylase activity is associated with improved glycemic homeostasis following starch ingestion in adults.
Mandel AL1, Breslin PA.
Author information
Abstract
In the current study, we determined whether increased digestion of starch by high salivary amylase concentrations predicted postprandial blood glucose following starch ingestion. Healthy, nonobese individuals were prescreened for salivary amylase activity and classified as high (HA) or low amylase (LA) if their activity levels per minute fell 1 SD higher or lower than the group mean, respectively. Fasting HA (n = 7) and LA (n = 7) individuals participated in 2 sessions during which they ingested either a starch (experimental) or glucose solution (control) on separate days. Blood samples were collected before, during, and after the participants drank each solution. The samples were analyzed for plasma glucose and insulin concentrations as well as diploid AMY1 gene copy number. HA individuals had significantly more AMY1 gene copies within their genomes than did the LA individuals. We found that following starch ingestion, HA individuals had significantly lower postprandial blood glucose concentrations at 45, 60, and 75 min, as well as significantly lower AUC and peak blood glucose concentrations than the LA individuals. Plasma insulin concentrations in the HA group were significantly higher than baseline early in the testing session, whereas insulin concentrations in the LA group did not increase at this time. Following ingestion of the glucose solution, however, blood glucose and insulin concentrations did not differ between the groups. These observations are interpreted to suggest that HA individuals may be better adapted to ingest starches, whereas LA individuals may be at greater risk for insulin resistance and diabetes if chronically ingesting starch-rich diets.
This fits nicely with the observation that some individuals seem better able to handle carbs than others and the idea that we can be divided into 'hunters' and 'farmers' such that people who cannot handle carbs well have a genome more like our ancient hunter gatherer ancestors whereas those who are able to cope with carbs have a genome that has been adapted to cope with the higher carb content of our more recent farmer ancestors.
Finally, I found this useful study suggesting that you might be able to make a guess as to how much amylase your saliva makes and hence how many copies of the gene you have by comparing how quickly your saliva dissolves starch:
http://www.ncbi.nlm.nih.gov/pubmed/20967220PLoS One. 2010 Oct 13;5(10):e13352. doi: 10.1371/journal.pone.0013352.
Individual differences in AMY1 gene copy number, salivary α-amylase levels, and the perception of oral starch.
Mandel AL1, Peyrot des Gachons C, Plank KL, Alarcon S, Breslin PA.
Author information
Abstract
BACKGROUND:
The digestion of dietary starch in humans is initiated by salivary α-amylase, an endo-enzyme that hydrolyzes starch into maltose, maltotriose and larger oligosaccharides. Salivary amylase accounts for 40 to 50% of protein in human saliva and rapidly alters the physical properties of starch. Importantly, the quantity and enzymatic activity of salivary amylase show significant individual variation. However, linking variation in salivary amylase levels with the oral perception of starch has proven difficult. Furthermore, the relationship between copy number variations (CNVs) in the AMY1 gene, which influence salivary amylase levels, and starch viscosity perception has not been explored.
PRINCIPAL FINDINGS:
Here we demonstrate that saliva containing high levels of amylase has sufficient activity to rapidly hydrolyze a viscous starch solution in vitro. Furthermore, we show with time-intensity ratings, which track the digestion of starch during oral manipulation, that individuals with high amylase levels report faster and more significant decreases in perceived starch viscosity than people with low salivary amylase levels. Finally, we demonstrate that AMY1 CNVs predict an individual's amount and activity of salivary amylase and thereby, ultimately determine their perceived rate of oral starch viscosity thinning.
CONCLUSIONS:
By linking genetic variation and its consequent salivary enzymatic differences to the perceptual sequellae of these variations, we show that AMY1 copy number relates to salivary amylase concentration and enzymatic activity level, which, in turn, account for individual variation in the oral perception of starch viscosity. The profound individual differences in salivary amylase levels and salivary activity may contribute significantly to individual differences in dietary starch intake and, consequently, to overall nutritional status.
Fascinating stuff! Thanks for bringing it to my attention!
xx
