Page URL:

Obesity linked to genetic variation in carbohydrate digestion

7 April 2014
Appeared in BioNews 749

Obesity might not simply be a matter of overeating or heightened appetite but is at least partially down to how we metabolise food, a study says.

Whereas previous research has concentrated on genes that influence appetite or eating behaviour to increase our likelihood of being overweight, new research has found that a gene involved in carbohydrate digestion may exert a strong influence. The findings suggest that two people of similar height and build could eat identical diets but only one would become overweight.

Dr Julia El-Sayed Moustafa, a co-lead author from Imperial College London, said: 'This paper is novel in that it identifies a genetic variation that is both common and has a relatively large effect on the risk of obesity in the general population'.

The researchers were interested in the effect of a phenomenon called copy number variation on body mass index (BMI). Copy number variation describes the fact that although people usually have two copies of each gene, this can vary in some sections of our DNA.

They started by looking at genetic data from a Swedish twin study involving 481 participants and soon found that copy number variation in AMY1, a gene coding for a digestive enzyme called salivary amylase seemed to exert a particularly strong effect on BMI. The more copies of AMY1 people had, the less likely they were to be obese.

The finding was repeated in two other datasets comprising genetic information from just under 6,000 people.

The number of copies of AMY1 is highly variable across the population. The researchers estimate that there is roughly a 20 percent decrease in the chance of becoming obese carried with every additional AMY1 gene.

Salivary amylase is the first enzyme encountered by food when it enters the mouth, beginning a digestive process that continues in the gut. People with fewer copies of the gene may have lower levels of the enzyme and so not break down carbohydrates as well as those with more copies.

However, first author Dr Mario Falchi told New Scientist that this explanation does not take into account amylase produced in the pancreas. He suggests that AMY1 copy number variation may exert its influence 'through more complex mechanisms such as influencing signalling pathways, or changing the gut microbiota'.

Joint lead investigator Professor Tim Spector of King's College London said that the knowledge that individual differences in metabolism can influence weight gain may have considerable impact on the public health approach to obesity.

'In the future, a simple blood or saliva test might be used to measure levels of key enzymes such as amylase in the body and therefore shape dietary advice for both overweight and underweight people', he said, before adding that 'treatments are a long way away'.

The research was published in Nature Genetics.

Genetic study supports link between carbohydrate digestion and obesity
Imperial College London (press release) |  31 March 2014
Low copy number of the salivary amylase gene predisposes to obesity
Nature Genetics |  31 March 2014
Obesity linked to our ability to digest carbohydrates
New Scientist |  30 March 2014
Salivary 'carb breakdown' gene linked to obesity, study shows
The Guardian |  30 March 2014
Strong link between obesity and 'carb breakdown' gene
King's College London (press release) |  31 March 2014
6 July 2015 - by Paul Waldron 
A new form of obesity and type 2 diabetes that is caused by a mutation in a single gene has been discovered...
16 February 2015 - by Kirsty Oswald 
A meta-analysis has found that around a fifth of variation in BMI is due to common genetic variation...
14 April 2014 - by Amanda Jefferys 
Weight loss improves both fertility and reproductive outcomes, and weight management medications and surgery are more effective than lifestyle interventions in achieving significant weight loss. Can infertility be considered a medical condition associated with obesity?...
24 March 2014 - by Dr Anna Cauldwell 
People with genes that predispose them to excess weight and obesity are more likely to put on weight from eating fried food, a study says...
17 March 2014 - by Dr Rosie Morley 
Scientists have identified a gene called IRX3 which is associated with obesity and may emerge as a serious contender as the most important 'fat gene' yet discovered...
23 March 2009 - by Rosie Beauchamp 
Researchers at the University of California, Berkeley, have published a study in the journal Cell that outlines their identification of a gene that is critical in turning carbohydrates into fat. The gene, called DNA-dependent protein kinase (DNA-PK), is a potential key to the prevention of obesity linked...
21 July 2008 - by Dr Rachael Panizzo 
Researchers at Imperial College London have identified a genetic link to obesity. Comparing the DNA of over 13,000 obese individuals to the DNA of non-obese control subjects, they identified three single nucleotide polymorphisms (SNPs) in the PCSK1 gene that were associated with obesity. The SNPs - single 'letter...
to add a Comment.

By posting a comment you agree to abide by the BioNews terms and conditions

Syndicate this story - click here to enquire about using this story.