Experts at the University of Nottingham have found there is no link between people with a low copy number of the salivary amylase gene (a digestive enzyme produced in the mouth) and being at a high risk of obesity, contrary to the findings of previous studies.
Salivary amylase is produced by the salivary glands in the mouth. It starts the digestive process by breaking down starch when you chew your food, converting it into maltose – a smaller carbohydrate.
In a study published in the journal Obesity, experts from the University's School of Life Sciences challenged the widely-publicised view that suggested that people with a low number of the salivary amylase gene were at a higher risk of obesity. This previous assumption could have potentially have provided an explanation as to why some people put on weight and others don't.
John Armour, Professor of Human Genetics and lead author of the study said: "After this initial claim was made, follow-up studies have failed to reproduce the association between this particular gene and BMI. The studies did, however, look at different groups of people from the original study, and in particular different age ranges.
After this initial claim was made, follow-up studies have failed to reproduce the association between this particular gene and BMI. The studies did, however, look at different groups of people from the original study, and in particular different age ranges. The association might therefore have been dependent on some feature of the population, and some of the features of the evidence suggested that the salivary amylase gene copy number might possibly be most important in children or younger adults."
The team's work built on these findings and was aimed at answering the specific question of whether there was an age-dependent association.
They did this by measuring amylase gene copy number (which doesn't change with age) in more than 1,000 people for whom they had measurements from birth to age 50 of BMI.
The team found no relationship at any age, which was consistent with the follow-up studies that failed to replicate an association.
"As a result we can say that, although carbohydrate intake is still important overall in people's weight variation, it looks like salivary amylase gene copy number variation is not a specific factor. In particular, our work implies that there is no basis for this kind of gene testing as part of a personalised approach to managing obesity," said Professor Armour.
He added: "In a way this is a pity, because it would have been a helpful way of specifically testing for, and understanding how individual variation in handling carbohydrates influences people's body weight – but unfortunately it just doesn't seem to be true."
