Obesity depends on your ability to digest carbohydrate

Staying off carbs to lose weight may be more useful to some than others, says a research suggesting that obesity may be linked to how our bodies digest the starch found in carbohydrate-rich foods like bread, rice and potatoes.

When we eat food, an enzyme in saliva called salivary amylase initiates digestion by breaking down some of the starch found in carbohydrates into sugars. This enzyme is produced by the gene AMY1.

AMY1 is an unusual gene as people can have multiple copies of it, unlike most genes where there are just two. The more copies you have, the more enzyme you produce. One theory is that humans evolved to carry more copies of the gene as our diets shifted towards carbohydrate-rich foods.

Mario Falchi at Imperial College London and colleagues compared the genome sequences of a group of siblings where one was overweight, the other lean. AMY1 gene was on top of the list.

The research team then studied a separate group of 5000 people from France and the UK and found that people with less than four copies of the gene were around eight times more likely to be obese than those with more than nine copies of the gene.

This suggests that people who are good at breaking down starch into sugars are less likely to be obese. However, why this should be the case isn’t clear from this study as it doesn’t take into account the amylase produced by the pancreas, says Falchi.

“It is possible that the effect of the salivary amylase genes isn’t directly influencing the digestion of carbs and how much energy we get from them,” he says. “It could be through more complex mechanisms such as influencing signalling pathways, or changing the gut microbiota.”

Studies to understand the mechanism are ongoing.

Don’t be disheartened if you are off carbs and yet not losing weight…it’s the genes!