Relationship between genetic variation, gut microbiome could help personalize nutrition recommendations

People with a high number of copies of a gene called AMY1, which expresses a salivary enzyme for breaking down starch, correlated strongly with a certain profile of gut and mouth bacteria, a discovery that could help nutritionists personalize recommendations to patients, according to a new study by researchers at Cornell University in Ithaca, New York, and published today in the journal Cell Host & Microbe.

A family of bacteria called Ruminococcaceae proliferates in the intestines when more of this salivary enzyme, called amylase, is available. The bacteria are known to break down resistant starch so it may be digested, something human amylases can't do. Degrading these hard to digest starches provides nutritional benefits.

In the study, researchers examined existing genetic and stool sample data from a British population of close to 1,000 individuals. They were looking for evidence of whether AMY1 gene copy numbers influence the microbiome, so they examined the results from a subset of 100 people from the British population, 50 with a predicted high copy number, top 5 percent, and 50 with a low copy number, bottom 5 percent.

Researchers then determined the number of AMY1 copies in more than 100 people from Ithaca, New York. They found a distribution of between two and 30 copies. The team also collected stool data and identified bacteria that associated with high and low AMY1 gene copy numbers.

Twenty-five of these study participants were then placed on a standardized diet for two weeks to make sure they were eating the same thing, and that they were eating starch, according to the study abstract. Afterward, the team collected saliva and stool samples and found that, in the gut, the results matched those from the British population study.

The results suggest the need for personalized nutrition, researchers said, in which medical professionals could take a patient's AMY1 gene copy number into account when giving dietary advice. Other researchers have associated the gene with glucose response to meals, insulin resistance and body mass index.

Furthermore, higher copy numbers of the AMY1 gene also correlated with higher levels of Porphyromonas, bacteria in the mouth associated with the gum disease periodontitis, though more study is needed.