Genetics Series: Salivary Amylase
I am going to start a new "series" of pieces here on the blog detailing the role of genetics in our appearance, performance, and health. Far too often I see individuals needlessly comparing themselves to others when in actuality, every individual is different, and even though you may appear to be similar to someone else in a lot of ways, the role your genes play in your life could be almost entirely different.
The primary purpose of this blog is to explain how these genetic differences influence much of what we can accomplish as human beings. Just because an individual can look a certain way or perform a certain way does not necessarily mean that they are a harder worker or that they have more dedication than you. Sure, hard work and dedication can improve your current situation, but it does not necessarily mean that you are going to be the best at something - despite what you may have been told.
Amylase is an enzyme that digests carbohydrates. It catalyses the hydrolysis of starch into sugars. It is released by both the pancreas and the salivary glands in your mouth. Sugary foods and beverages actually start digesting in the mouth of mammals due to the release of amylase during that first phase of digestion. Despite the fact that virtually everyone possesses an almost identical amylase gene, some individuals have more copies of the gene than others, therefore increasing their ability to produce amylase.
The following study looked to understand the relationship between amylase production and obesity.
Common multi-allelic copy number variants (CNVs) appear enriched for phenotypic associations compared to their biallelic counterparts1, 2, 3, 4. Here we investigated the influence of gene dosage effects on adiposity through a CNV association study of gene expression levels in adipose tissue. We identified significant association of a multi-allelic CNV encompassing the salivary amylase gene (AMY1) with body mass index (BMI) and obesity, and we replicated this finding in 6,200 subjects. Increased AMY1 copy number was positively associated with both amylase gene expression (P = 2.31 × 10−14) and serum enzyme levels (P < 2.20 × 10−16), whereas reduced AMY1 copy number was associated with increased BMI (change in BMI per estimated copy = −0.15 (0.02) kg/m2; P = 6.93 × 10−10) and obesity risk (odds ratio (OR) per estimated copy = 1.19, 95% confidence interval (CI) = 1.13–1.26; P = 1.46 × 10−10). The OR value of 1.19 per copy of AMY1 translates into about an eightfold difference in risk of obesity between subjects in the top (copy number > 9) and bottom (copy number < 4) 10% of the copy number distribution. Our study provides a first genetic link between carbohydrate metabolism and BMI and demonstrates the power of integrated genomic approaches beyond genome-wide association studies.
What they found was that the individuals with the most copies (more than 9) of the amylase gene, had a lowered risk of obesity. On the other hand, individuals with fewer copies of the amylase gene (less than 4) had an increased risk of obesity. We could speculate as to the reasons why more genes are beneficial in a couple of ways.
First, increased amylase production could increase the rate of carbohydrate metabolism (digestion and absorption) right in the mouth, thereby increasing the rate at which the carbohydrates enter the bloodstream, stunting the severity and intensity of a blood sugar spike. We know that the quicker and more abrupt one's blood sugar rises, the more intense the subsequent blood sugar crash may be. Wildly fluctuating blood sugar levels can lead to cravings of more sugar, so it is generally recommended that individuals consume carbohydrates that do not cause too high of a blood sugar spike (see: Glycemic Index). Therefore, an increase in amylase production may help to slow the overall metabolism of ingested carbohydrates by starting the process earlier (in the mouth).
Also, an increase in amylase production may also help to trigger our brains into being satiated sooner by starting the process of carbohydrate metabolism in the mouth versus waiting until the sugar reaches our intestines and absorbed into the bloodstream that way. Digested carbohydrates (glucose) are not absorbed through the stomach walls, and in fact amylase is inhibited in stomach acid, so by the time an individual consumes carbs, has them broken down in the stomach, passed on to the small intestine, and then absorbed into the bloodstream, they may have consumed far more carbs than they initially intended.
So how is this important? Well, as the first blog in this Genetics Series, we are looking to understand how different we can be as humans. Despite the fact that many of us look the same and are relatively similar, especially from a genetics standpoint, many of us interact with exercise, our diets, and world we live in in drastically different ways at times. Just because an individual is overweight or skinny, does not necessarily indicate their affinity for a healthy lifestyle or not. If you are overweight, understand that you may have certain genetic disadvantages that you have to work a bit harder at some things than others. Having said that, everyone will have advantages and disadvantages, I try and encourage clients of mine to not allow the disadvantages define who they are or cause them to simply give up hope.
Tyler Robbins B.Sc. CSCS
Director of Fitness
Head of CrossFit