Thinking of carbohydrates, many people immediately picture bread, potatoes, and pasta, but carbs come in many healthy forms — whole grains, vegetables, and fruits. Carbs are a necessary part of the diet and provide the body with glucose, which is converted to energy. Unfortunately, overeating carbs often leads to obesity… but not for everyone. Now, a new study conducted at King's College London and Imperial College London suggests a "carb breakdown" gene exists, and it may help to explain all these differences. In fact, people with fewer copies of this gene, which instructs the body to make a carb-digesting enzyme, are less effective in digesting certain foods and so they are at higher risk of obesity.

Amlyase is an enzyme that breaks carbohydrates down to sugar, which is converted to energy used by the body. The amylase that resides in the mouth, salivary amlyase, begins the process of carbohydrate digestion, while pancreatic amylase continues that process in the small intestine. Two amylase genes exist, AMY1 and AMY2, coding for salivary and pancreatic amylase, respectively.

For the study, the team of researchers began by measuring expression of these genes in 149 Swedish families. Immediately, they discovered unusual patterns around AMY1 and AMY2, and they believed the variations to be directly related to obesity. Next, they turned to TwinsUK, the biggest UK adult twin registry, and found similar patterns in 972 twins. Analyzing and checking the data, they realized that the total number of AMY1 genes was linked to obesity. In fact, participants with the lowest number of copies of that gene had an eight times increase in the risk of obesity when compared with participants with the lowest number of copies of that gene.

Not yet satisfied, the researchers decided to verify their results by estimating the precise copy numbers of the amylase gene in the DNA of 481 additional Swedish participants, 1,479 additional TwinsUK participants, and 2,137 participants in a similar French study. All showed the same pattern between a decreased number of AMY1 and obesity. Looking at another continent, the researchers discovered that Chinese patients also repeated the pattern.

"These findings are very exciting,” said Dr. Tim Spector, head of the Department of Twin Research and Genetic Epidemiology at King's College London. In a press release, he further explained his research: “While studies to date have mainly found small effect genes that alter eating behaviour, 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.”

The study results suggest that people with fewer copies of the AMY1 gene have more difficulty breaking down carbohydrates than those with more copies making a greater number of enzymes. The discovery suggests that people's bodies react individually to the same type and amount of food. "The next step is to find out more about the activity of this digestive enzyme, and whether this might prove a useful biomarker or target for the treatment of obesity,” Spector said. "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."

 

Source: Falchi M,  El-Sayed Moustafa JS, Takousis P, et al. Low copy number of the salivary amylase gene predisposes to obesity. Nature Genetics. 2014.