In a new research, scientists have discovered that weight gain may have to do more with the genes linked to the digestive system than with appetite. People with fewer copies of a gene coding for a carbohydrates-digesting enzyme may be at higher risk of obesity, the study found. "We discovered how the digestive 'tools' in your metabolism vary between people - and the genes coding for these - can have a large influence on your weight," said Tim Spector, a professor at King's College London. The research indicated that people's bodies may react differently to the same type and amount of food, leading to weight gain in some and not in others. Therefore dietary advice may need to be more tailored to an individual's digestive system, based on whether they have the genetic predisposition and necessary enzymes to digest different foods, the study suggested. The new study found that people with fewer copies of the AMY1 gene have lower levels of salivary amylase, an enzyme that plays a significant role in breaking down carbohydrates in the mouth at the start of the digestion process. For the study, researchers measured gene expression patterns in families with differences in the levels of obesity and found unusual patterns around two amylase genes (AMY1 and AMY2), which code for salivary and pancreatic amylase. A lower estimated AMY1 copy-number showed a significantly increased risk of obesity in all the people and this translated to an approximate eight-fold difference in the risk of obesity between those with the highest number of copies of the gene and those with the lowest. The study appeared in the journal Nature Genetics.