Understanding Genetic Differences in Carb Metabolism

Written by: Kevin Cann

There is nothing more controversial in the nutrition world than 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.


  1. says

    That’s a shot over the bow of people who like to oversimplify things … it’s all about trying things out and seeing if it works. If it doesn’t … try something else!

  2. rs711 says

    Hi Kevin,

    I’ll have to look into those studies at some point since it’s quite surprising that in one of the studies you mentioned starch seemed to keep blood glucose levels ‘high’ for longer. Although not all that surprising considering the breakdown takes more time, but shouldn’t the peak level also be lower…? (more questions questions questions)

    IMHO, a question worth asking is: will knowing the carbohydrate TOLERANCE level(s) of various people tell us much about what level(s) these people actually THRIVE on?

    And here we get into the murky waters of defining ‘thriving’ for different people…for an athlete that might be thought of in terms of performance whilst for an overweight office worker that might rather mean focus, cravings and weight normalisation..what say you Mr. Cann – ideas?

    Nice write-up by the way :)

  3. Kevin Cann says

    Blood glucose stayed elevated longer in the low AMY1 group compared to the high. This is probably a result from having fewer tools to breakdown the starch. Amylase doesn’t need to breakdown glucose the same way as starch. Glucose is ready to go to be used. This is why there was no difference in blood sugar levels between the two groups when the glucose was ingested.

    I think knowing the carb tolerance would be beneficial. It takes the guesswork out. More research needs to be done before conclusions are made, but the biggest takeaway is that we are all different and this variability needs to be understood for treatment. There is no one size fits all approach.

  4. Matt says

    Hmm interesting… I would have thought that having more amylase in the saliva would have led to a faster uptake in blood glucose levels since the starch is converted to glucose quicker. I guess the reason the high AMY1 group have lower blood glucose levels is that they’re able to anticipate the glucose load coming from the starch and accordingly coordinate their insulin release. The low AMY1 group not only take longer to break down the starch but also maybe their metabolism doesn’t even recognise the glucose load that will eventuate when it is broken down leading to prolonged, elevated levels of blood glucose.

    • Nate says

      Thanks, Matt. I was confused by people with a low number of AMY1 genes having higher blood sugars right at the beginning of the test. I was only thinking of the digestion part of the body and not all of its communication parts. I’m embarrassed to think that my thinking was similar to that of those who think ‘a calorie is a calorie’.

      To me this study shows again that the human body is not a closed system. One cannot calculate the exact effect of food calories on the weight of a person. By food calories I mean those released in a high temperature metal box. The way the body utilizes its food is complicated and will be, I think, impossible to determine, except by testing each person with each food and even combination of foods.

    • Booth says

      The “anticipation” you mention is related to nutrient absorption physiology: A glucose load delivered orally stimulates a greater insulin response than one delivered by IV. So someone with more salivary amylase will see a larger oral glucose load from a given amount of starch, and subsequently release more insulin and more rapidly manage blood glucose levels.

  5. says

    I’m starting to think the same type of genetic variation is probably true for any number of nutritional factors: optimal n-3/n-6 intake, beta-carotene to vitamin A conversion, etc. I would say sunlight and vitamin D, but if you’ve followed Chris Masterjohn’s latest work, it looks like some of the most deeply held beliefs (theories?) on that are in question now. If you come from genetic stock where your ancestors were likely coastal people, then maybe your genes “expect” you to consume more preformed EPA & DHA, so you might be a “poor converter” of ALA to these longer chain fats. Same with vitamin A — let’s say your ancestors got more of their total food from plants rather than animals. Maybe you’re a better converter of b-carotene to vitamin A. The list of places this can go is LONG.

    This is where I think the future of nutrigenomics and genetic medicine is — in evaluating what particular genotypes likely do best with and recommending diet and lifestyle changes best suited for the individual. It should have nothing to do with genetics in the sense of, “All the men in my family have heart disease, so I’m gonna get it too, and there’s nothing I can do about it.”

    Seems like the bottom line is that no particular dietary strategy can be recommended across the board, for *everyone.* (Beyond just straight up real, whole, unprocessed food.) Low-carb, high-carb, low plant fiber, lots of plants, heavy on the fish, heavy on land animals…*that’s* maybe where the details have to be tailored to the individual and their genetic makeup. Obviously there are some unalterable facts about human metabolism and fuel partitioning, but the human race does seem to thrive on a wide variety of macronutrient intakes, provided those ratios match up with your body’s “expectations.” (People always bust out the Kitavans vs the Inuit, but they never seem to suggest that maybe the reason one stays healthy and robust on lots of fruit & starch and one thrives on marine blubber and protein is because they’re wired differently — enzymatically, especially. Take a Pacific Islander and stick him in the Arctic Circle and see how he does on seal oil, and take an Arctic dweller and see if they can stay lean and modern illness-free on mangoes and pineapples. One diet isn’t “better” than the other; there’s just one that’s more suitable for a particular genetic makeup versus the other.

  6. Paul says

    This is a great article, and helps me understand why I feel great and “lean out” on a high-carb diet, while my wife does not. Is it possible to determine how many copies of the AMY1 gene we each have? I would be interested in seeing a little scientific proof that my body is designed for a higher-carb (yet still Paleo) diet.


      • Jennz says

        My drs office pulled a genetics test from Pathways Genomics.. turns out I am a low carb type with poor a, b, c, d, e conversion..so much for raw til 4 diet.. heading back to high raw with eggs fish mostly greens nuts oils little fruit.. strange thing is I always feel best on that anyway.. caution though the dam test wasbilled at $5,000 my insurance doesn’t cover it..they are totally scamming on price.. I got an IMMENSELY helpful life saving liver pathways test at Genova for $400 it explained why I have had severe allergic reactions to meds and ended up in icu ..and tons of chemical and med sensitivities..if there is any one test I would say is worth it is the one from Genova called Detoxigenomic.. other than that I feel the Pathways genomics was a total waste..I have excellent body feedback about diet and had concluded the same on my own

  7. Susie says

    I’m sorry, I have to quibble. There are a few times in this post where you use “then” when you should use “than”. You should use “than” whenever making a comparison, such as “They know more about their body THAN science does” because you are comparing their knowledge with the knowledge of science.

    Othwerwise, this is a great post. This research is fascinating and I can’t wait to see where it leads us as we continue to study the effect of genetics on our diet.

    Thanks so much for sharing! 😀

  8. Erica says

    I second Paul’s question… Is it possible to determine how many copies of the AMY1 gene we each have?

    I have been following a low carb Paleo diet for over a year — really leaned out, felt good and then recently gained a bit of weight and felt tired all the time. From there I took the advice of an online dietitian/fitness pro and went with a higher protein, low fat, higher carb diet and seemed to lose a bit of weight about 3 weeks in — then gained again.

    I realize the body takes time to adjust to using different sources for fuel, but how much time do you think should be spent experimenting before moving on to try something new? 8 weeks? 3 months? Something else?

    Thanks for the great post!

  9. Martin says

    I wonder if the people who produce enough AMY1 enzyme to break down sugar effectively when they are young do so in the older age. I know quite a few people who thrived on a higher-carb diet when they where younger, very lean & sporty and their health deteriorated when they got older (got fat, not so sporty any more and developed several symptoms of the metabolic syndrome).

  10. says

    I too would like to know how to find out my number of AMY1 gene. Being adopted and having NO medical history I feel like I am flying blind at times. Ok all the time when it comes to medical issues.

  11. Sherry R says

    First sentence: than* -I immediately discredited everything after that as non scholarly & can never use this as a resource.

  12. Lana says

    A few people have asked about getting tested for copy numbers of AMY1… I guess that’s not a common test yet?
    I read the study you are commenting on and then found your article. Thank you for helping to clarify it. It really is something that the HA people had lower blood glucose than the LA group after consuming starches!

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