Wednesday, January 14, 2015

Obesity genes and me

The BBC science programme Horizon is currently running a three part series on the science of dieting. They have identified three categories of the obese and one - the 'constant cravers' - are defined by having 'obesity genes'.

It seems likely that I'm a 'constant craver'.

A little internet research provides a short list which can be cross-correlated with my 23andMe genotype download.

1. The FTO gene

As Wikipedia explains: "In 2009 variants in the FTO gene were further confirmed to associate with obesity in two very large genome-wide association studies of body mass index (BMI). It was shown that adults bearing the at-risk AT and AA alleles at rs9939609 consumed between 125 and 280 Calories per day than those carrying the protective TT genotype," (c. 5-12% of the daily allowance).

A quick search of my Excel spreadsheet for rs9939609 confirms I'm AT at this location. No wonder I was thirteen and a half stone before starting the 5:2 diet (I'm now at 11 stone = 70 kg but not without continuing maintenance). As a carrier of one of the 'A' risk alleles my disposition to obesity is 30% higher than that of baseline TT people.

2. The MC4R gene

"Mutations in the MC4R gene account for 6-8% of obesity cases. A common variant of the MC4R gene, distributed in about 22% of the population, increases the risk for weight gain by causing increased appetite and decreased satiety. Calorie restriction through portion control and smart food choices is the best strategy for weight loss for people carrying this variant."

The relevant SNP is rs17782313 where C alleles are associated with higher body mass index (BMI). The three options are CC, CT, TT - where TT is baseline normal, CT is associated with a BMI increase of 0.22 units and CC with a BMI increase of 0.44 units. As is so often the case, the allele effects are, as you see, additive.

What am I?  Yep, it's bad: CC.

3  The ADIPOQ gene

The relevant allele is rs17366568. "A significant genotypic association was observed between ADIPOQ rs17366568 and obesity. The frequencies of AG and AA genotypes were significantly higher in the obese group (11%) than in the non-obese group (5%) (P=0.024). The odds of A alleles occurring among the obese group were twice those among the non-obese group (odds ratio 2.15; 95% confidence interval 1.13-4.09)." (From here).

At last some good news! I am GG at this location.


Doubtlessly I'll return to this topic when more is known, especially as the results to-date are so personally depressing!