The Carb Gene
Alannah Mezzatesta, BSc
Nutrition Scientist (ANutr)
last updated 27th July 2022
Let's be honest. Carbs are delicious. There are few things more comforting than tucking into a hearty bowl of pasta or some good ol' bread and butter. Yet, devastatingly, carb is a dirty word these days. You're hard pressed to find someone who hasn't cut carbs from their diet at some point in their lives.
But what if it didn't have to be that way?
For some genetically blessed humans among us, carbs are not the villainous enemy they're made out to be and can actually be enjoyed regularly as part of a balanced diet. The explanation, however, lies in our genes.
Humans possess a gene called AMY1 which codes for the salivary enzyme, amylase. When we eat a starchy food, amylase is responsible for breaking down the starch in our mouths into smaller units.
Starch is a type of carbohydrate, along with sugar and fibre. It is classed as a complex carbohydrate and is the most commonly consumed carb in our diets. It is present in foods such as bread, pasta, rice, grains, beans, corn, potatoes and other root vegetables.
Research has found that humans exhibit variations in the number of AMY1 gene copies they have . The average person has 6 copies, however it ranges from 2-18. Generally, the higher the number of copies you possess, the more amylase enzyme you express in your saliva which may influence how efficiently you break down and process dietary starch. So, some people may be more capable of digesting these carbohydrates compared to others .
Interestingly, the AMY1 gene has evolved over generations to have an increased number of copies . This is likely to have occurred in response to shifting to a high-starch diet as higher copies of the AMY1 gene are seen in populations with high-starch diets such as American-Europeans and Japanese, compared to those with traditionally low-starch diets such as the Biaka, rainforest hunter-gatherers and the Yakut fishing/cattle farmers.
Similar patterns are seen in dogs , likely arising from domestication as they evolved to adapt to life as man?s best friend, feeding on human food scraps.
What does this mean for me?
The real life implications of this information depends on whether you have a high or low AMY1 gene copy number. Studies have shown that, on a high-starch diet, people with lower copy numbers may have an increased risk of obesity, insulin resistance and type-2 diabetes, while those with higher copy numbers show lower insulin levels and insulin resistance and a decreased risk of type 2 diabetes .
These findings suggest that people with higher AMY1 copy numbers may benefit more from a high-starch diet (i.e. A diet rich in root vegetables, cereals, and whole grains).
Those with lower copy numbers may be more suited to a low-starch diet enjoying foods such as leafy greens, non-root vegetables, fish and lean meats, citrus fruits and berries, and foods higher in resistant starch to promote gut health  (see article on Resistant Starch).
Interestingly, exercise (particularly high-intensity exercise), has been shown to increase your salivary amylase activity , effectively increasing your ability to breakdown and digest starch. So, low copy number individuals could also consider including regular high-intensity exercise such as cycling or swimming along-side a healthy low-starch diet.
Where to from here?
It is important to note that the relationship between AMY1 gene copy numbers and starch digestibly is not so straightforward. There are many other influencing factors that affect an individual?s metabolism so this doesn?t grant you a free pass to load up on all the carbs you want nor should you despairingly resign yourself to a carb-less life of celery juices and cauliflower pizza.
The good news is, there are genetic tests available on the market, such as myGene's own CarbGene test, that you can take to find out your number of AMY1 gene copies and the suggested lifestyle changes you can make, based on your results, to optimise your health.