Starch digestion begins in the mouth, before you have even swallowed. An enzyme called salivary amylase starts breaking down long starch chains the moment you chew. Yet not everyone produces the same amount, and the reason lies in a remarkable genetic quirk.
A gene you count, rather than read
Most genetic variants are single-letter changes in the DNA. The AMY1 gene, which encodes salivary amylase, is different: what varies is the number of copies of the gene. Where one person carries 2 copies, another may carry 10, 15, or more. The more copies you have, the more amylase you secrete in your saliva.
A landmark study by Perry and colleagues (2007) showed that populations with traditionally high-starch diets carry, on average, more AMY1 copies than populations whose diets are low in starch. It is one of the first documented examples of natural selection acting on gene copy number, shaped directly by diet.
More copies, better starch digestion
AMY1 copy number correlates positively with salivary amylase levels: more copies mean earlier, more efficient starch breakdown. Conversely, low copy number has been associated in some studies with higher body mass index, though the findings remain debated.
The gene-diet interaction is the heart of it
AMY1's effect only makes sense in the context of what you eat. In the Malmö cohort, the association between starch intake and insulin markers was considerably more favourable in people carrying 10 or more copies. In other words, a starch-rich diet does not have the same metabolic effect depending on your AMY1 endowment. Same plate, different responses.
What this means in practice
You cannot change your copy number, but you can adapt your approach to carbohydrates:
- Favour slow-digesting carbohydrates (legumes, oats, whole grains) over refined starch, especially if you tolerate blood-sugar spikes poorly.
- Chew thoroughly: salivary amylase only acts during the oral phase, so prolonged chewing maximises its work.
- Pair starch with fibre, protein, or fat to slow glucose absorption.
This variability in starch response is exactly what nutrigenetics aims to personalise. Your FuelYourDNA profile examines key genes in carbohydrate metabolism and insulin sensitivity to refine your recommendations, beyond one-size-fits-all nutrition advice.
Scientific References
- Perry GH, et al. (2007). Diet and the evolution of human amylase gene copy number variation. Nature Genetics, 39(10), 1256–1260. PubMed 17828263
- Carpenter D, et al. (2015). Obesity, starch digestion and amylase: copy number variants at AMY1 and AMY2. Human Molecular Genetics, 24(12), 3472–3480. DOI 10.1093/hmg/ddv098
- Koder Hamid A, et al. (2021). Interaction between AMY1 copy number variation and starch intake on glucose homeostasis (Malmö Diet and Cancer Cohort). Frontiers in Nutrition, 7, 598850. DOI 10.3389/fnut.2020.598850
- Janiak MC, et al. (2019). Independent amylase gene copy number bursts correlate with dietary preferences in mammals. eLife, 8, e44628. PubMed 31084707