Amylase but we do have genetic variations.
New research indicates that obesity in the general population may be genetically linked to how our bodies digest carbohydrates.
Published today in the journal
Nature Genetics, the study investigated the relationship between body weight and a gene called AMY1, which is responsible for an enzyme present in our saliva known as salivary amylase. This enzyme is the first to be encountered by food when it enters the mouth, and it begins the process of starch digestion that then continues in the gut.
People usually have two copies of each gene, but in some regions of our DNA there can be variability in the number of copies a person carries, which is known as copy number variation. The number of copies of AMY1 can be highly variable between people, and it is believed that higher numbers of copies of the salivary amylase gene have evolved in response to a shift towards diets containing more starch since prehistoric times.
Researchers from Imperial College London, in collaboration with other international institutions, looked at the number of copies of the gene AMY1 present in the DNA of thousands of people from the UK, France, Sweden and Singapore. They found that people who carried a low number of copies of the salivary amylase gene were at greater risk of obesity.
The chance of being obese for people with less than four copies of the AMY1 gene was approximately eight times higher than in those with more than nine copies of this gene. The researchers estimated that with every additional copy of the salivary amylase gene there was approximately a 20 per cent decrease in the odds of becoming obese
http://www3.imperial.ac.uk/newsandeventspggrp/imperialcollege/newssummary/news_31-3-2014-9-58-51
Starchy diet, extra genes.
http://genetics.thetech.org/original_news/news62