Understanding Genetic Differences in Carb Metabolism
Written by: Kevin Cann
There is nothing more controversial in the nutrition world then carbohydrates. There are some people/groups that condemn carbohydrates as a terrorist infiltrating our society. At the other end of the spectrum we have people/groups that condemn fat in the same manner and preach a higher carbohydrate diet for the masses. There is research that supports both arguments so who are we supposed to believe? The answer lies in your genome.
Our gene pool began to differentiate between one another when we began to settle in various locations around the globe. Some hunter-gatherer groups settled in cold climates, some in warm climates, and everything in between. Each location offered its own challenges and evolutionary pressures, one of them being diet.
For example, colder climates may have relied more heavily on animal meats for food and warmer, wetter climates may have relied more heavily on plant food (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2377015/#R8). This led to diversity in one specific gene responsible for the breakdown of carbohydrates, alpha-amylase (AMY1). AMY1 is a salivary enzyme that begins the breakdown of starch in the mouth and makes it taste sweet.
AMY1 variation exists between different members of the human species. This may be a major reason why there is so much variation from person to person when it comes to carbohydrate intake. Some people thrive on a higher carbohydrate diet and others thrive when carbohydrates are kept in check. This is also a reason why there will never be just one perfect human diet.
The USDA recommends that the entire population consumes 45% to 65% of their daily calories in the form of starch. Is this a correct recommendation to the part of the population that contains fewer copies of the AMY1 gene? It is not only unfair, but may be setting them up for a future filled with weight issues and all the diseases that accompany increased weight.
Abigail Manell and Paul Breslin have done some amazing research at the Monell Chemical Senses Center in Philadelphia. One study in particular looked at starch digestion between differing AMY1 groups. The experimental group was healthy, non-obese individuals and they were divided into a high amylase group and a low amylase group. They came into the lab twice, once to ingest starch (experiment) and glucose (control). The low amylase group had higher blood glucose levels then the high amylase group during starch consumption. This increase in blood glucose levels lasted for the two hours that the participants remained at the lab! Interestingly, when the low amylase group consumed the glucose blood sugar levels remained relatively consistent with the high amylase group and the blood sugar did not stay elevated as long as when they ingested the starch (http://jn.nutrition.org/content/142/5/853.abstract).
Recommending a high starch diet to people with low amylase gene copies is setting them up for insulin resistance and diabetes. Another thing to think about is the diversity within each group. Humans can contain anywhere between 2 and 15 copies of the AMY1 gene (http://www.plosone.org/article/info:doi/10.1371/journal.pone.0013352). This means there is a wide difference from person to person on blood glucose levels following the exact same intake of starch.
The research by Manell and Braslin was published in the Journal of Nutrition in 2012. This is an extremely new phenomenon when looking at the individuality of carbohydrate digestion. All we know about this topic is that some people respond to the same meal of starch differently. We do not know optimal starch intake for each variation yet. 45% to 65% of calories coming from starch may still be too much for even the people that contain 15 copies of AMY1 gene, we do not know the tolerable upper intake level.
Underlying inflammation is also going to be a variable. Carbohydrate metabolism gets dysfunctional when inflammation is present. Someone with 15 copies of the AMY1 gene that exercises, sleeps well, has friends, and manages stress may respond more favorable to the same starch meal that someone with 15 copies that is sedentary. Also, food quality is still going to play a role. Just because someone has a higher number of AMY1 copies does not mean eating a high grain diet will be beneficial, remember the inflammation piece.
Who knows where the future of this information will take us. It does bring to light a few things. Everyone is truly their own unique snowflake. It also brings to light that there is a lot we do not know about the human body. We need to remain humble and actually listen to our patients/clients. They know more about their body then science does.