The Link Between Metabolism and Obesity

As a dietitian I often find myself instructing patients to lower their intake of carbohydrates, in fact I’ve said it so many times, and to so many patients, that at times I feel like a broken record.

Previous genetic studies into obesity have tended to focus on how genetic variations alter our appetites and food behaviours. However, a new study recently published in Nature Genetics piqued my interest as it suggests that there may in fact be a rather novel genetic link between metabolism and obesity.

The study authored by Dr. Mario Falchi from the School of Public Health at Imperial College London investigated the relationship between obesity and a gene called AMY1, the gene responsible for an enzyme present in our saliva known as salivary amylase, the enzyme first encountered by food when it enters the mouth that begins the process of starch digestion.

"We are now starting to develop a clearer picture of a combination of genetic factors affecting psychological and metabolic processes that contribute to people's chances of becoming obese. This should ultimately help us to find better ways of tackling obesity," Dr. Mario Falchi says.

The number of copies of a gene that a person carries can vary throughout their DNA, although people usually have two copies of each gene. Yet, Dr. Mario Falchi and his team found that the number of copies of this particular AMY1 gene can vary greatly between people.

The researchers examined the number of copies of AMY1 present in the DNA of more than 6,000 people from four different countries: the UK, France, Sweden and Singapore. And according to their results, it is those who have a lower number of AMY1 who are most likely to become obese. They determined that AMY1 was the gene that had the greatest influence on body weight and then counted the number of times the gene was repeated in each individual and how this affected their obesity risk.

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.

This new discovery highlights a strong link between metabolism and obesity and suggests that goes someway to proving that our bodies react differently to the same type and amount of food, leading to weight gain in some but not in others. How we deal with carbohydrates and hence, how much carbohydrate we should be consuming, must be adjusted for each individual. This research indicates genetics may play a role in obesity, and carbohydrate metabolism is very much involved.